Merge pull request #5179 from roc-lang/i5143-tuple-abilities

Implement ability obligation checking and derivation for tuples

crates/compiler/builtins/roc/Decode.roc

@@ -23,6 +23,7 @@ interface Decode
         string,
         list,
         record,
+        tuple,
         custom,
         decodeWith,
         fromBytesPartial,
@@ -43,6 +44,7 @@ interface Decode
             I32,
             I64,
             I128,
+            Nat,
             F32,
             F64,
             Dec,
@@ -76,8 +78,24 @@ DecoderFormatting has
     bool : Decoder Bool fmt | fmt has DecoderFormatting
     string : Decoder Str fmt | fmt has DecoderFormatting
     list : Decoder elem fmt -> Decoder (List elem) fmt | fmt has DecoderFormatting
+
+    ## `record state stepField finalizer` decodes a record field-by-field.
+    ##
+    ## `stepField` returns a decoder for the given field in the record, or
+    ## `Skip` if the field is not a part of the decoded record.
+    ##
+    ## `finalizer` should produce the record value from the decoded `state`.
     record : state, (state, Str -> [Keep (Decoder state fmt), Skip]), (state -> Result val DecodeError) -> Decoder val fmt | fmt has DecoderFormatting
 
+    ## `tuple state stepElem finalizer` decodes a tuple element-by-element.
+    ##
+    ## `stepElem` returns a decoder for the nth index in the tuple, or
+    ## `TooLong` if the index is larger than the expected size of the tuple. The
+    ## index passed to `stepElem` is 0-indexed.
+    ##
+    ## `finalizer` should produce the tuple value from the decoded `state`.
+    tuple : state, (state, Nat -> [Next (Decoder state fmt), TooLong]), (state -> Result val DecodeError) -> Decoder val fmt | fmt has DecoderFormatting
+
 custom : (List U8, fmt -> DecodeResult val) -> Decoder val fmt | fmt has DecoderFormatting
 custom = \decode -> @Decoder decode
 

crates/compiler/builtins/roc/Encode.roc

@@ -22,6 +22,7 @@ interface Encode
         list,
         record,
         tag,
+        tuple,
         custom,
         appendWith,
         append,
@@ -69,6 +70,7 @@ EncoderFormatting has
     string : Str -> Encoder fmt | fmt has EncoderFormatting
     list : List elem, (elem -> Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
     record : List { key : Str, value : Encoder fmt } -> Encoder fmt | fmt has EncoderFormatting
+    tuple : List (Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
     tag : Str, List (Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
 
 custom : (List U8, fmt -> List U8) -> Encoder fmt | fmt has EncoderFormatting

crates/compiler/builtins/roc/Json.roc

@@ -96,6 +96,7 @@ Json := {} has [
              string: encodeString,
              list: encodeList,
              record: encodeRecord,
+             tuple: encodeTuple,
              tag: encodeTag,
          },
          DecoderFormatting {
@@ -116,6 +117,7 @@ Json := {} has [
              string: decodeString,
              list: decodeList,
              record: decodeRecord,
+             tuple: decodeTuple,
          },
      ]
 
@@ -207,6 +209,25 @@ encodeRecord = \fields ->
 
         List.append bytesWithRecord (Num.toU8 '}')
 
+encodeTuple = \elems ->
+    Encode.custom \bytes, @Json {} ->
+        writeTuple = \{ buffer, elemsLeft }, elemEncoder ->
+            bufferWithElem =
+                appendWith buffer elemEncoder (@Json {})
+
+            bufferWithSuffix =
+                if elemsLeft > 1 then
+                    List.append bufferWithElem (Num.toU8 ',')
+                else
+                    bufferWithElem
+
+            { buffer: bufferWithSuffix, elemsLeft: elemsLeft - 1 }
+
+        bytesHead = List.append bytes (Num.toU8 '[')
+        { buffer: bytesWithRecord } = List.walk elems { buffer: bytesHead, elemsLeft: List.len elems } writeTuple
+
+        List.append bytesWithRecord (Num.toU8 ']')
+
 encodeTag = \name, payload ->
     Encode.custom \bytes, @Json {} ->
         # Idea: encode `A v1 v2` as `{"A": [v1, v2]}`
@@ -477,6 +498,12 @@ openBrace = \bytes -> parseExactChar bytes '{'
 closingBrace : List U8 -> DecodeResult {}
 closingBrace = \bytes -> parseExactChar bytes '}'
 
+openBracket : List U8 -> DecodeResult {}
+openBracket = \bytes -> parseExactChar bytes '['
+
+closingBracket : List U8 -> DecodeResult {}
+closingBracket = \bytes -> parseExactChar bytes ']'
+
 recordKey : List U8 -> DecodeResult Str
 recordKey = \bytes -> jsonString bytes
 
@@ -527,6 +554,36 @@ decodeRecord = \initialState, stepField, finalizer -> Decode.custom \bytes, @Jso
             Ok val -> { result: Ok val, rest: afterRecordBytes }
             Err e -> { result: Err e, rest: afterRecordBytes }
 
+decodeTuple = \initialState, stepElem, finalizer -> Decode.custom \initialBytes, @Json {} ->
+        # NB: the stepper function must be passed explicitly until #2894 is resolved.
+        decodeElems = \stepper, state, index, bytes ->
+            { val: newState, rest: beforeCommaOrBreak } <- tryDecode
+                    (
+                        when stepper state index is
+                            TooLong ->
+                                { rest: beforeCommaOrBreak } <- bytes |> anything |> tryDecode
+                                { result: Ok state, rest: beforeCommaOrBreak }
+
+                            Next decoder ->
+                                Decode.decodeWith bytes decoder (@Json {})
+                    )
+
+            { result: commaResult, rest: nextBytes } = comma beforeCommaOrBreak
+
+            when commaResult is
+                Ok {} -> decodeElems stepElem newState (index + 1) nextBytes
+                Err _ -> { result: Ok newState, rest: nextBytes }
+
+        { rest: afterBracketBytes } <- initialBytes |> openBracket |> tryDecode
+
+        { val: endStateResult, rest: beforeClosingBracketBytes } <- decodeElems stepElem initialState 0 afterBracketBytes |> tryDecode
+
+        { rest: afterTupleBytes } <- beforeClosingBracketBytes |> closingBracket |> tryDecode
+
+        when finalizer endStateResult is
+            Ok val -> { result: Ok val, rest: afterTupleBytes }
+            Err e -> { result: Err e, rest: afterTupleBytes }
+
 # Helper to eat leading Json whitespace characters
 eatWhitespace = \input ->
     when input is

crates/compiler/can/src/debug/pretty_print.rs

@@ -330,7 +330,11 @@ fn expr<'a>(c: &Ctx, p: EPrec, f: &'a Arena<'a>, e: &'a Expr) -> DocBuilder<'a,
         } => expr(c, AppArg, f, &loc_expr.value)
             .append(f.text(format!(".{}", field.as_str())))
             .group(),
-        TupleAccess { .. } => todo!(),
+        TupleAccess {
+            loc_expr, index, ..
+        } => expr(c, AppArg, f, &loc_expr.value)
+            .append(f.text(format!(".{index}")))
+            .group(),
         OpaqueWrapFunction(OpaqueWrapFunctionData { opaque_name, .. }) => {
             f.text(format!("@{}", opaque_name.as_str(c.interns)))
         }

crates/compiler/derive/src/decoding/list.rs

@@ -0,0 +1,104 @@
+use roc_can::expr::Expr;
+
+use roc_error_macros::internal_error;
+use roc_module::called_via::CalledVia;
+
+use roc_module::symbol::Symbol;
+use roc_region::all::Loc;
+use roc_types::subs::{Content, FlatType, GetSubsSlice, SubsSlice, Variable};
+use roc_types::types::AliasKind;
+
+use crate::decoding::wrap_in_decode_custom_decode_with;
+use crate::synth_var;
+use crate::util::Env;
+
+pub(crate) fn decoder(env: &mut Env<'_>, _def_symbol: Symbol) -> (Expr, Variable) {
+    // Build
+    //
+    //   def_symbol : Decoder (List elem) fmt | elem has Decoding, fmt has DecoderFormatting
+    //   def_symbol = Decode.custom \bytes, fmt -> Decode.decodeWith bytes (Decode.list Decode.decoder) fmt
+    //
+    // NB: reduction to `Decode.list Decode.decoder` is not possible to the HRR.
+
+    use Expr::*;
+
+    // Decode.list Decode.decoder : Decoder (List elem) fmt
+    let (decode_list_call, this_decode_list_ret_var) = {
+        // List elem
+        let elem_var = env.subs.fresh_unnamed_flex_var();
+
+        // Decode.decoder : Decoder elem fmt | elem has Decoding, fmt has EncoderFormatting
+        let (elem_decoder, elem_decoder_var) = {
+            // build `Decode.decoder : Decoder elem fmt` type
+            // Decoder val fmt | val has Decoding, fmt has EncoderFormatting
+            let elem_decoder_var = env.import_builtin_symbol_var(Symbol::DECODE_DECODER);
+
+            // set val ~ elem
+            let val_var = match env.subs.get_content_without_compacting(elem_decoder_var) {
+                Content::Alias(Symbol::DECODE_DECODER_OPAQUE, vars, _, AliasKind::Opaque)
+                    if vars.type_variables_len == 2 =>
+                {
+                    env.subs.get_subs_slice(vars.type_variables())[0]
+                }
+                _ => internal_error!("Decode.decode not an opaque type"),
+            };
+
+            env.unify(val_var, elem_var);
+
+            (
+                AbilityMember(Symbol::DECODE_DECODER, None, elem_decoder_var),
+                elem_decoder_var,
+            )
+        };
+
+        // Build `Decode.list Decode.decoder` type
+        // Decoder val fmt -[uls]-> Decoder (List val) fmt | fmt has DecoderFormatting
+        let decode_list_fn_var = env.import_builtin_symbol_var(Symbol::DECODE_LIST);
+
+        // Decoder elem fmt -a-> b
+        let elem_decoder_var_slice = SubsSlice::insert_into_subs(env.subs, [elem_decoder_var]);
+        let this_decode_list_clos_var = env.subs.fresh_unnamed_flex_var();
+        let this_decode_list_ret_var = env.subs.fresh_unnamed_flex_var();
+        let this_decode_list_fn_var = synth_var(
+            env.subs,
+            Content::Structure(FlatType::Func(
+                elem_decoder_var_slice,
+                this_decode_list_clos_var,
+                this_decode_list_ret_var,
+            )),
+        );
+
+        //   Decoder val  fmt -[uls]-> Decoder (List val) fmt | fmt has DecoderFormatting
+        // ~ Decoder elem fmt -a    -> b
+        env.unify(decode_list_fn_var, this_decode_list_fn_var);
+
+        let decode_list_member = AbilityMember(Symbol::DECODE_LIST, None, this_decode_list_fn_var);
+        let decode_list_fn = Box::new((
+            decode_list_fn_var,
+            Loc::at_zero(decode_list_member),
+            this_decode_list_clos_var,
+            this_decode_list_ret_var,
+        ));
+
+        let decode_list_call = Call(
+            decode_list_fn,
+            vec![(elem_decoder_var, Loc::at_zero(elem_decoder))],
+            CalledVia::Space,
+        );
+
+        (decode_list_call, this_decode_list_ret_var)
+    };
+
+    let bytes_sym = env.new_symbol("bytes");
+    let fmt_sym = env.new_symbol("fmt");
+    let fmt_var = env.subs.fresh_unnamed_flex_var();
+    let captures = vec![];
+
+    wrap_in_decode_custom_decode_with(
+        env,
+        bytes_sym,
+        (fmt_sym, fmt_var),
+        captures,
+        (decode_list_call, this_decode_list_ret_var),
+    )
+}

crates/compiler/derive/src/decoding/record.rs

@@ -0,0 +1,990 @@
+use roc_can::expr::{
+    AnnotatedMark, ClosureData, Expr, Field, Recursive, WhenBranch, WhenBranchPattern,
+};
+use roc_can::pattern::Pattern;
+use roc_collections::SendMap;
+use roc_module::called_via::CalledVia;
+use roc_module::ident::Lowercase;
+use roc_module::symbol::Symbol;
+use roc_region::all::{Loc, Region};
+use roc_types::subs::{
+    Content, ExhaustiveMark, FlatType, LambdaSet, OptVariable, RecordFields, RedundantMark,
+    SubsSlice, TagExt, UnionLambdas, UnionTags, Variable,
+};
+use roc_types::types::RecordField;
+
+use crate::synth_var;
+use crate::util::{Env, ExtensionKind};
+
+use super::wrap_in_decode_custom_decode_with;
+
+/// Implements decoding of a record. For example, for
+///
+/// ```text
+///   {first: a, second: b}
+/// ```
+///
+/// we'd like to generate an impl like
+///
+/// ```roc
+/// decoder : Decoder {first: a, second: b} fmt | a has Decoding, b has Decoding, fmt has DecoderFormatting
+/// decoder =
+///     initialState : {f0: Result a [NoField], f1: Result b [NoField]}
+///     initialState = {f0: Err NoField, f1: Err NoField}
+///
+///     stepField = \state, field ->
+///         when field is
+///             "first" ->
+///                 Keep (Decode.custom \bytes, fmt ->
+///                     when Decode.decodeWith bytes Decode.decoder fmt is
+///                         {result, rest} ->
+///                             {result: Result.map result \val -> {state & f0: Ok val}, rest})
+///             "second" ->
+///                 Keep (Decode.custom \bytes, fmt ->
+///                     when Decode.decodeWith bytes Decode.decoder fmt is
+///                         {result, rest} ->
+///                             {result: Result.map result \val -> {state & f1: Ok val}, rest})
+///             _ -> Skip
+///
+///     finalizer = \{f0, f1} ->
+///         when f0 is
+///             Ok first ->
+///                 when f1 is
+///                     Ok second -> Ok {first, second}
+///                     Err NoField -> Err TooShort
+///             Err NoField -> Err TooShort
+///
+///     Decode.custom \bytes, fmt -> Decode.decodeWith bytes (Decode.record initialState stepField finalizer) fmt
+/// ```
+pub(crate) fn decoder(
+    env: &mut Env,
+    _def_symbol: Symbol,
+    fields: Vec<Lowercase>,
+) -> (Expr, Variable) {
+    // The decoded type of each field in the record, e.g. {first: a, second: b}.
+    let mut field_vars = Vec::with_capacity(fields.len());
+    // The type of each field in the decoding state, e.g. {first: Result a [NoField], second: Result b [NoField]}
+    let mut result_field_vars = Vec::with_capacity(fields.len());
+
+    // initialState = ...
+    let (initial_state_var, initial_state) =
+        initial_state(env, &fields, &mut field_vars, &mut result_field_vars);
+
+    // finalizer = ...
+    let (finalizer, finalizer_var, decode_err_var) = finalizer(
+        env,
+        initial_state_var,
+        &fields,
+        &field_vars,
+        &result_field_vars,
+    );
+
+    // stepField = ...
+    let (step_field, step_var) = step_field(
+        env,
+        fields,
+        &field_vars,
+        &result_field_vars,
+        initial_state_var,
+        decode_err_var,
+    );
+
+    // Build up the type of `Decode.record` we expect
+    let record_decoder_var = env.subs.fresh_unnamed_flex_var();
+    let decode_record_lambda_set = env.subs.fresh_unnamed_flex_var();
+    let decode_record_var = env.import_builtin_symbol_var(Symbol::DECODE_RECORD);
+    let this_decode_record_var = {
+        let flat_type = FlatType::Func(
+            SubsSlice::insert_into_subs(env.subs, [initial_state_var, step_var, finalizer_var]),
+            decode_record_lambda_set,
+            record_decoder_var,
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    env.unify(decode_record_var, this_decode_record_var);
+
+    // Decode.record initialState stepField finalizer
+    let call_decode_record = Expr::Call(
+        Box::new((
+            this_decode_record_var,
+            Loc::at_zero(Expr::AbilityMember(
+                Symbol::DECODE_RECORD,
+                None,
+                this_decode_record_var,
+            )),
+            decode_record_lambda_set,
+            record_decoder_var,
+        )),
+        vec![
+            (initial_state_var, Loc::at_zero(initial_state)),
+            (step_var, Loc::at_zero(step_field)),
+            (finalizer_var, Loc::at_zero(finalizer)),
+        ],
+        CalledVia::Space,
+    );
+
+    let (call_decode_custom, decode_custom_ret_var) = {
+        let bytes_sym = env.new_symbol("bytes");
+        let fmt_sym = env.new_symbol("fmt");
+        let fmt_var = env.subs.fresh_unnamed_flex_var();
+
+        let (decode_custom, decode_custom_var) = wrap_in_decode_custom_decode_with(
+            env,
+            bytes_sym,
+            (fmt_sym, fmt_var),
+            vec![],
+            (call_decode_record, record_decoder_var),
+        );
+
+        (decode_custom, decode_custom_var)
+    };
+
+    (call_decode_custom, decode_custom_ret_var)
+}
+
+// Example:
+// stepField = \state, field ->
+//     when field is
+//         "first" ->
+//             Keep (Decode.custom \bytes, fmt ->
+//                 # Uses a single-branch `when` because `let` is more expensive to monomorphize
+//                 # due to checks for polymorphic expressions, and `rec` would be polymorphic.
+//                 when Decode.decodeWith bytes Decode.decoder fmt is
+//                     rec ->
+//                         {
+//                             rest: rec.rest,
+//                             result: when rec.result is
+//                                 Ok val -> Ok {state & first: Ok val},
+//                                 Err err -> Err err
+//                         })
+//
+//         "second" ->
+//             Keep (Decode.custom \bytes, fmt ->
+//                 when Decode.decodeWith bytes Decode.decoder fmt is
+//                     rec ->
+//                         {
+//                             rest: rec.rest,
+//                             result: when rec.result is
+//                                 Ok val -> Ok {state & second: Ok val},
+//                                 Err err -> Err err
+//                         })
+//
+//         _ -> Skip
+fn step_field(
+    env: &mut Env,
+    fields: Vec<Lowercase>,
+    field_vars: &[Variable],
+    result_field_vars: &[Variable],
+    state_record_var: Variable,
+    decode_err_var: Variable,
+) -> (Expr, Variable) {
+    let state_arg_symbol = env.new_symbol("stateRecord");
+    let field_arg_symbol = env.new_symbol("field");
+
+    // +1 because of the default branch.
+    let mut branches = Vec::with_capacity(fields.len() + 1);
+    let keep_payload_var = env.subs.fresh_unnamed_flex_var();
+    let keep_or_skip_var = {
+        let keep_payload_subs_slice = SubsSlice::insert_into_subs(env.subs, [keep_payload_var]);
+        let flat_type = FlatType::TagUnion(
+            UnionTags::insert_slices_into_subs(
+                env.subs,
+                [
+                    ("Keep".into(), keep_payload_subs_slice),
+                    ("Skip".into(), Default::default()),
+                ],
+            ),
+            TagExt::Any(Variable::EMPTY_TAG_UNION),
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    for ((field_name, &field_var), &result_field_var) in fields
+        .into_iter()
+        .zip(field_vars.iter())
+        .zip(result_field_vars.iter())
+    {
+        // Example:
+        // "first" ->
+        //     Keep (Decode.custom \bytes, fmt ->
+        //         # Uses a single-branch `when` because `let` is more expensive to monomorphize
+        //         # due to checks for polymorphic expressions, and `rec` would be polymorphic.
+        //         when Decode.decodeWith bytes Decode.decoder fmt is
+        //             rec ->
+        //                 {
+        //                     rest: rec.rest,
+        //                     result: when rec.result is
+        //                         Ok val -> Ok {state & first: Ok val},
+        //                         Err err -> Err err
+        //                 }
+        //     )
+
+        let this_custom_callback_var;
+        let custom_callback_ret_var;
+        let custom_callback = {
+            // \bytes, fmt ->
+            //     when Decode.decodeWith bytes Decode.decoder fmt is
+            //         rec ->
+            //             {
+            //                 rest: rec.rest,
+            //                 result: when rec.result is
+            //                     Ok val -> Ok {state & first: Ok val},
+            //                     Err err -> Err err
+            //             }
+            let bytes_arg_symbol = env.new_symbol("bytes");
+            let fmt_arg_symbol = env.new_symbol("fmt");
+            let bytes_arg_var = env.subs.fresh_unnamed_flex_var();
+            let fmt_arg_var = env.subs.fresh_unnamed_flex_var();
+
+            // rec.result : [Ok field_var, Err DecodeError]
+            let rec_dot_result = {
+                let tag_union = FlatType::TagUnion(
+                    UnionTags::for_result(env.subs, field_var, decode_err_var),
+                    TagExt::Any(Variable::EMPTY_TAG_UNION),
+                );
+
+                synth_var(env.subs, Content::Structure(tag_union))
+            };
+
+            // rec : { rest: List U8, result: (typeof rec.result) }
+            let rec_var = {
+                let fields = RecordFields::insert_into_subs(
+                    env.subs,
+                    [
+                        ("rest".into(), RecordField::Required(Variable::LIST_U8)),
+                        ("result".into(), RecordField::Required(rec_dot_result)),
+                    ],
+                );
+                let record = FlatType::Record(fields, Variable::EMPTY_RECORD);
+
+                synth_var(env.subs, Content::Structure(record))
+            };
+
+            // `Decode.decoder` for the field's value
+            let decoder_var = env.import_builtin_symbol_var(Symbol::DECODE_DECODER);
+            let decode_with_var = env.import_builtin_symbol_var(Symbol::DECODE_DECODE_WITH);
+            let lambda_set_var = env.subs.fresh_unnamed_flex_var();
+            let this_decode_with_var = {
+                let subs_slice = SubsSlice::insert_into_subs(
+                    env.subs,
+                    [bytes_arg_var, decoder_var, fmt_arg_var],
+                );
+                let this_decode_with_var = synth_var(
+                    env.subs,
+                    Content::Structure(FlatType::Func(subs_slice, lambda_set_var, rec_var)),
+                );
+
+                env.unify(decode_with_var, this_decode_with_var);
+
+                this_decode_with_var
+            };
+
+            // The result of decoding this field's value - either the updated state, or a decoding error.
+            let when_expr_var = {
+                let flat_type = FlatType::TagUnion(
+                    UnionTags::for_result(env.subs, state_record_var, decode_err_var),
+                    TagExt::Any(Variable::EMPTY_TAG_UNION),
+                );
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            // What our decoder passed to `Decode.custom` returns - the result of decoding the
+            // field's value, and the remaining bytes.
+            custom_callback_ret_var = {
+                let rest_field = RecordField::Required(Variable::LIST_U8);
+                let result_field = RecordField::Required(when_expr_var);
+                let flat_type = FlatType::Record(
+                    RecordFields::insert_into_subs(
+                        env.subs,
+                        [("rest".into(), rest_field), ("result".into(), result_field)],
+                    ),
+                    Variable::EMPTY_RECORD,
+                );
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            let custom_callback_body = {
+                let rec_symbol = env.new_symbol("rec");
+
+                // # Uses a single-branch `when` because `let` is more expensive to monomorphize
+                // # due to checks for polymorphic expressions, and `rec` would be polymorphic.
+                // when Decode.decodeWith bytes Decode.decoder fmt is
+                //     rec ->
+                //         {
+                //             rest: rec.rest,
+                //             result: when rec.result is
+                //                 Ok val -> Ok {state & first: Ok val},
+                //                 Err err -> Err err
+                //         }
+                let branch_body = {
+                    let result_val = {
+                        // result: when rec.result is
+                        //     Ok val -> Ok {state & first: Ok val},
+                        //     Err err -> Err err
+                        let ok_val_symbol = env.new_symbol("val");
+                        let err_val_symbol = env.new_symbol("err");
+                        let ok_branch_expr = {
+                            // Ok {state & first: Ok val},
+                            let mut updates = SendMap::default();
+
+                            updates.insert(
+                                field_name.clone(),
+                                Field {
+                                    var: result_field_var,
+                                    region: Region::zero(),
+                                    loc_expr: Box::new(Loc::at_zero(Expr::Tag {
+                                        tag_union_var: result_field_var,
+                                        ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                        name: "Ok".into(),
+                                        arguments: vec![(
+                                            field_var,
+                                            Loc::at_zero(Expr::Var(ok_val_symbol, field_var)),
+                                        )],
+                                    })),
+                                },
+                            );
+
+                            let updated_record = Expr::RecordUpdate {
+                                record_var: state_record_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                symbol: state_arg_symbol,
+                                updates,
+                            };
+
+                            Expr::Tag {
+                                tag_union_var: when_expr_var,
+                                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                name: "Ok".into(),
+                                arguments: vec![(state_record_var, Loc::at_zero(updated_record))],
+                            }
+                        };
+
+                        let branches = vec![
+                            // Ok val -> Ok {state & first: Ok val},
+                            WhenBranch {
+                                patterns: vec![WhenBranchPattern {
+                                    pattern: Loc::at_zero(Pattern::AppliedTag {
+                                        whole_var: rec_dot_result,
+                                        ext_var: Variable::EMPTY_TAG_UNION,
+                                        tag_name: "Ok".into(),
+                                        arguments: vec![(
+                                            field_var,
+                                            Loc::at_zero(Pattern::Identifier(ok_val_symbol)),
+                                        )],
+                                    }),
+                                    degenerate: false,
+                                }],
+                                value: Loc::at_zero(ok_branch_expr),
+                                guard: None,
+                                redundant: RedundantMark::known_non_redundant(),
+                            },
+                            // Err err -> Err err
+                            WhenBranch {
+                                patterns: vec![WhenBranchPattern {
+                                    pattern: Loc::at_zero(Pattern::AppliedTag {
+                                        whole_var: rec_dot_result,
+                                        ext_var: Variable::EMPTY_TAG_UNION,
+                                        tag_name: "Err".into(),
+                                        arguments: vec![(
+                                            decode_err_var,
+                                            Loc::at_zero(Pattern::Identifier(err_val_symbol)),
+                                        )],
+                                    }),
+                                    degenerate: false,
+                                }],
+                                value: Loc::at_zero(Expr::Tag {
+                                    tag_union_var: when_expr_var,
+                                    ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                    name: "Err".into(),
+                                    arguments: vec![(
+                                        decode_err_var,
+                                        Loc::at_zero(Expr::Var(err_val_symbol, decode_err_var)),
+                                    )],
+                                }),
+                                guard: None,
+                                redundant: RedundantMark::known_non_redundant(),
+                            },
+                        ];
+
+                        // when rec.result is
+                        //     Ok val -> Ok {state & first: Ok val},
+                        //     Err err -> Err err
+                        Expr::When {
+                            loc_cond: Box::new(Loc::at_zero(Expr::RecordAccess {
+                                record_var: rec_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                field_var: rec_dot_result,
+                                loc_expr: Box::new(Loc::at_zero(Expr::Var(rec_symbol, rec_var))),
+                                field: "result".into(),
+                            })),
+                            cond_var: rec_dot_result,
+                            expr_var: when_expr_var,
+                            region: Region::zero(),
+                            branches,
+                            branches_cond_var: rec_dot_result,
+                            exhaustive: ExhaustiveMark::known_exhaustive(),
+                        }
+                    };
+
+                    // {
+                    //     rest: rec.rest,
+                    //     result: when rec.result is
+                    //         Ok val -> Ok {state & first: Ok val},
+                    //         Err err -> Err err
+                    // }
+                    let mut fields_map = SendMap::default();
+
+                    fields_map.insert(
+                        "rest".into(),
+                        Field {
+                            var: Variable::LIST_U8,
+                            region: Region::zero(),
+                            loc_expr: Box::new(Loc::at_zero(Expr::RecordAccess {
+                                record_var: rec_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                field_var: Variable::LIST_U8,
+                                loc_expr: Box::new(Loc::at_zero(Expr::Var(rec_symbol, rec_var))),
+                                field: "rest".into(),
+                            })),
+                        },
+                    );
+
+                    // result: when rec.result is
+                    //     Ok val -> Ok {state & first: Ok val},
+                    //     Err err -> Err err
+                    fields_map.insert(
+                        "result".into(),
+                        Field {
+                            var: when_expr_var,
+                            region: Region::zero(),
+                            loc_expr: Box::new(Loc::at_zero(result_val)),
+                        },
+                    );
+
+                    Expr::Record {
+                        record_var: custom_callback_ret_var,
+                        fields: fields_map,
+                    }
+                };
+
+                let branch = WhenBranch {
+                    patterns: vec![WhenBranchPattern {
+                        pattern: Loc::at_zero(Pattern::Identifier(rec_symbol)),
+                        degenerate: false,
+                    }],
+                    value: Loc::at_zero(branch_body),
+                    guard: None,
+                    redundant: RedundantMark::known_non_redundant(),
+                };
+
+                let condition_expr = Expr::Call(
+                    Box::new((
+                        this_decode_with_var,
+                        Loc::at_zero(Expr::Var(Symbol::DECODE_DECODE_WITH, this_decode_with_var)),
+                        lambda_set_var,
+                        rec_var,
+                    )),
+                    vec![
+                        (
+                            Variable::LIST_U8,
+                            Loc::at_zero(Expr::Var(bytes_arg_symbol, Variable::LIST_U8)),
+                        ),
+                        (
+                            decoder_var,
+                            Loc::at_zero(Expr::AbilityMember(
+                                Symbol::DECODE_DECODER,
+                                None,
+                                decoder_var,
+                            )),
+                        ),
+                        (
+                            fmt_arg_var,
+                            Loc::at_zero(Expr::Var(fmt_arg_symbol, fmt_arg_var)),
+                        ),
+                    ],
+                    CalledVia::Space,
+                );
+
+                // when Decode.decodeWith bytes Decode.decoder fmt is
+                Expr::When {
+                    loc_cond: Box::new(Loc::at_zero(condition_expr)),
+                    cond_var: rec_var,
+                    expr_var: custom_callback_ret_var,
+                    region: Region::zero(),
+                    branches: vec![branch],
+                    branches_cond_var: rec_var,
+                    exhaustive: ExhaustiveMark::known_exhaustive(),
+                }
+            };
+
+            let custom_closure_symbol = env.new_symbol("customCallback");
+            this_custom_callback_var = env.subs.fresh_unnamed_flex_var();
+            let custom_callback_lambda_set_var = {
+                let content = Content::LambdaSet(LambdaSet {
+                    solved: UnionLambdas::insert_into_subs(
+                        env.subs,
+                        [(custom_closure_symbol, [state_record_var])],
+                    ),
+                    recursion_var: OptVariable::NONE,
+                    unspecialized: Default::default(),
+                    ambient_function: this_custom_callback_var,
+                });
+                let custom_callback_lambda_set_var = synth_var(env.subs, content);
+                let subs_slice =
+                    SubsSlice::insert_into_subs(env.subs, [bytes_arg_var, fmt_arg_var]);
+
+                env.subs.set_content(
+                    this_custom_callback_var,
+                    Content::Structure(FlatType::Func(
+                        subs_slice,
+                        custom_callback_lambda_set_var,
+                        custom_callback_ret_var,
+                    )),
+                );
+
+                custom_callback_lambda_set_var
+            };
+
+            // \bytes, fmt -> …
+            Expr::Closure(ClosureData {
+                function_type: this_custom_callback_var,
+                closure_type: custom_callback_lambda_set_var,
+                return_type: custom_callback_ret_var,
+                name: custom_closure_symbol,
+                captured_symbols: vec![(state_arg_symbol, state_record_var)],
+                recursive: Recursive::NotRecursive,
+                arguments: vec![
+                    (
+                        bytes_arg_var,
+                        AnnotatedMark::known_exhaustive(),
+                        Loc::at_zero(Pattern::Identifier(bytes_arg_symbol)),
+                    ),
+                    (
+                        fmt_arg_var,
+                        AnnotatedMark::known_exhaustive(),
+                        Loc::at_zero(Pattern::Identifier(fmt_arg_symbol)),
+                    ),
+                ],
+                loc_body: Box::new(Loc::at_zero(custom_callback_body)),
+            })
+        };
+
+        let decode_custom_ret_var = env.subs.fresh_unnamed_flex_var();
+        let decode_custom = {
+            let decode_custom_var = env.import_builtin_symbol_var(Symbol::DECODE_CUSTOM);
+            let decode_custom_closure_var = env.subs.fresh_unnamed_flex_var();
+            let this_decode_custom_var = {
+                let subs_slice = SubsSlice::insert_into_subs(env.subs, [this_custom_callback_var]);
+                let flat_type =
+                    FlatType::Func(subs_slice, decode_custom_closure_var, decode_custom_ret_var);
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            env.unify(decode_custom_var, this_decode_custom_var);
+
+            // Decode.custom \bytes, fmt -> …
+            Expr::Call(
+                Box::new((
+                    this_decode_custom_var,
+                    Loc::at_zero(Expr::Var(Symbol::DECODE_CUSTOM, this_decode_custom_var)),
+                    decode_custom_closure_var,
+                    decode_custom_ret_var,
+                )),
+                vec![(this_custom_callback_var, Loc::at_zero(custom_callback))],
+                CalledVia::Space,
+            )
+        };
+
+        env.unify(keep_payload_var, decode_custom_ret_var);
+
+        let keep = {
+            // Keep (Decode.custom \bytes, fmt ->
+            //     when Decode.decodeWith bytes Decode.decoder fmt is
+            //         rec ->
+            //             {
+            //                 rest: rec.rest,
+            //                 result: when rec.result is
+            //                     Ok val -> Ok {state & first: Ok val},
+            //                     Err err -> Err err
+            //             }
+            // )
+            Expr::Tag {
+                tag_union_var: keep_or_skip_var,
+                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                name: "Keep".into(),
+                arguments: vec![(decode_custom_ret_var, Loc::at_zero(decode_custom))],
+            }
+        };
+
+        let branch = {
+            // "first" ->
+            //     Keep (Decode.custom \bytes, fmt ->
+            //         when Decode.decodeWith bytes Decode.decoder fmt is
+            //             rec ->
+            //                 {
+            //                     rest: rec.rest,
+            //                     result: when rec.result is
+            //                         Ok val -> Ok {state & first: Ok val},
+            //                         Err err -> Err err
+            //                 }
+            //     )
+            WhenBranch {
+                patterns: vec![WhenBranchPattern {
+                    pattern: Loc::at_zero(Pattern::StrLiteral(field_name.into())),
+                    degenerate: false,
+                }],
+                value: Loc::at_zero(keep),
+                guard: None,
+                redundant: RedundantMark::known_non_redundant(),
+            }
+        };
+
+        branches.push(branch);
+    }
+
+    // Example: `_ -> Skip`
+    let default_branch = WhenBranch {
+        patterns: vec![WhenBranchPattern {
+            pattern: Loc::at_zero(Pattern::Underscore),
+            degenerate: false,
+        }],
+        value: Loc::at_zero(Expr::Tag {
+            tag_union_var: keep_or_skip_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: "Skip".into(),
+            arguments: Vec::new(),
+        }),
+        guard: None,
+        redundant: RedundantMark::known_non_redundant(),
+    };
+
+    branches.push(default_branch);
+
+    // when field is
+    let body = Expr::When {
+        loc_cond: Box::new(Loc::at_zero(Expr::Var(field_arg_symbol, Variable::STR))),
+        cond_var: Variable::STR,
+        expr_var: keep_or_skip_var,
+        region: Region::zero(),
+        branches,
+        branches_cond_var: Variable::STR,
+        exhaustive: ExhaustiveMark::known_exhaustive(),
+    };
+
+    let step_field_closure = env.new_symbol("stepField");
+    let function_type = env.subs.fresh_unnamed_flex_var();
+    let closure_type = {
+        let lambda_set = LambdaSet {
+            solved: UnionLambdas::tag_without_arguments(env.subs, step_field_closure),
+            recursion_var: OptVariable::NONE,
+            unspecialized: Default::default(),
+            ambient_function: function_type,
+        };
+
+        synth_var(env.subs, Content::LambdaSet(lambda_set))
+    };
+
+    {
+        let args_slice = SubsSlice::insert_into_subs(env.subs, [state_record_var, Variable::STR]);
+
+        env.subs.set_content(
+            function_type,
+            Content::Structure(FlatType::Func(args_slice, closure_type, keep_or_skip_var)),
+        )
+    };
+
+    let expr = Expr::Closure(ClosureData {
+        function_type,
+        closure_type,
+        return_type: keep_or_skip_var,
+        name: step_field_closure,
+        captured_symbols: Vec::new(),
+        recursive: Recursive::NotRecursive,
+        arguments: vec![
+            (
+                state_record_var,
+                AnnotatedMark::known_exhaustive(),
+                Loc::at_zero(Pattern::Identifier(state_arg_symbol)),
+            ),
+            (
+                Variable::STR,
+                AnnotatedMark::known_exhaustive(),
+                Loc::at_zero(Pattern::Identifier(field_arg_symbol)),
+            ),
+        ],
+        loc_body: Box::new(Loc::at_zero(body)),
+    });
+
+    (expr, function_type)
+}
+
+// Example:
+// finalizer = \rec ->
+//     when rec.first is
+//         Ok first ->
+//             when rec.second is
+//                 Ok second -> Ok {first, second}
+//                 Err NoField -> Err TooShort
+//         Err NoField -> Err TooShort
+fn finalizer(
+    env: &mut Env,
+    state_record_var: Variable,
+    fields: &[Lowercase],
+    field_vars: &[Variable],
+    result_field_vars: &[Variable],
+) -> (Expr, Variable, Variable) {
+    let state_arg_symbol = env.new_symbol("stateRecord");
+    let mut fields_map = SendMap::default();
+    let mut pattern_symbols = Vec::with_capacity(fields.len());
+    let decode_err_var = {
+        let flat_type = FlatType::TagUnion(
+            UnionTags::tag_without_arguments(env.subs, "TooShort".into()),
+            TagExt::Any(Variable::EMPTY_TAG_UNION),
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    for (field_name, &field_var) in fields.iter().zip(field_vars.iter()) {
+        let symbol = env.new_symbol(field_name.as_str());
+
+        pattern_symbols.push(symbol);
+
+        let field_expr = Expr::Var(symbol, field_var);
+        let field = Field {
+            var: field_var,
+            region: Region::zero(),
+            loc_expr: Box::new(Loc::at_zero(field_expr)),
+        };
+
+        fields_map.insert(field_name.clone(), field);
+    }
+
+    // The bottom of the happy path - return the decoded record {first: a, second: b} wrapped with
+    // "Ok".
+    let return_type_var;
+    let mut body = {
+        let subs = &mut env.subs;
+        let record_field_iter = fields
+            .iter()
+            .zip(field_vars.iter())
+            .map(|(field_name, &field_var)| (field_name.clone(), RecordField::Required(field_var)));
+        let flat_type = FlatType::Record(
+            RecordFields::insert_into_subs(subs, record_field_iter),
+            Variable::EMPTY_RECORD,
+        );
+        let done_record_var = synth_var(subs, Content::Structure(flat_type));
+        let done_record = Expr::Record {
+            record_var: done_record_var,
+            fields: fields_map,
+        };
+
+        return_type_var = {
+            let flat_type = FlatType::TagUnion(
+                UnionTags::for_result(subs, done_record_var, decode_err_var),
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            );
+
+            synth_var(subs, Content::Structure(flat_type))
+        };
+
+        Expr::Tag {
+            tag_union_var: return_type_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: "Ok".into(),
+            arguments: vec![(done_record_var, Loc::at_zero(done_record))],
+        }
+    };
+
+    // Unwrap each result in the decoded state
+    //
+    // when rec.first is
+    //     Ok first -> ...happy path...
+    //     Err NoField -> Err TooShort
+    for (((symbol, field_name), &field_var), &result_field_var) in pattern_symbols
+        .iter()
+        .rev()
+        .zip(fields.iter().rev())
+        .zip(field_vars.iter().rev())
+        .zip(result_field_vars.iter().rev())
+    {
+        // when rec.first is
+        let cond_expr = Expr::RecordAccess {
+            record_var: state_record_var,
+            ext_var: env.new_ext_var(ExtensionKind::Record),
+            field_var: result_field_var,
+            loc_expr: Box::new(Loc::at_zero(Expr::Var(state_arg_symbol, state_record_var))),
+            field: field_name.clone(),
+        };
+
+        // Example: `Ok x -> expr`
+        let ok_branch = WhenBranch {
+            patterns: vec![WhenBranchPattern {
+                pattern: Loc::at_zero(Pattern::AppliedTag {
+                    whole_var: result_field_var,
+                    ext_var: Variable::EMPTY_TAG_UNION,
+                    tag_name: "Ok".into(),
+                    arguments: vec![(field_var, Loc::at_zero(Pattern::Identifier(*symbol)))],
+                }),
+                degenerate: false,
+            }],
+            value: Loc::at_zero(body),
+            guard: None,
+            redundant: RedundantMark::known_non_redundant(),
+        };
+
+        // Example: `_ -> Err TooShort`
+        let err_branch = WhenBranch {
+            patterns: vec![WhenBranchPattern {
+                pattern: Loc::at_zero(Pattern::Underscore),
+                degenerate: false,
+            }],
+            value: Loc::at_zero(Expr::Tag {
+                tag_union_var: return_type_var,
+                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                name: "Err".into(),
+                arguments: vec![(
+                    decode_err_var,
+                    Loc::at_zero(Expr::Tag {
+                        tag_union_var: decode_err_var,
+                        ext_var: Variable::EMPTY_TAG_UNION,
+                        name: "TooShort".into(),
+                        arguments: Vec::new(),
+                    }),
+                )],
+            }),
+            guard: None,
+            redundant: RedundantMark::known_non_redundant(),
+        };
+
+        body = Expr::When {
+            loc_cond: Box::new(Loc::at_zero(cond_expr)),
+            cond_var: result_field_var,
+            expr_var: return_type_var,
+            region: Region::zero(),
+            branches: vec![ok_branch, err_branch],
+            branches_cond_var: result_field_var,
+            exhaustive: ExhaustiveMark::known_exhaustive(),
+        };
+    }
+
+    let function_var = synth_var(env.subs, Content::Error); // We'll fix this up in subs later.
+    let function_symbol = env.new_symbol("finalizer");
+    let lambda_set = LambdaSet {
+        solved: UnionLambdas::tag_without_arguments(env.subs, function_symbol),
+        recursion_var: OptVariable::NONE,
+        unspecialized: Default::default(),
+        ambient_function: function_var,
+    };
+    let closure_type = synth_var(env.subs, Content::LambdaSet(lambda_set));
+    let flat_type = FlatType::Func(
+        SubsSlice::insert_into_subs(env.subs, [state_record_var]),
+        closure_type,
+        return_type_var,
+    );
+
+    // Fix up function_var so it's not Content::Error anymore
+    env.subs
+        .set_content(function_var, Content::Structure(flat_type));
+
+    let finalizer = Expr::Closure(ClosureData {
+        function_type: function_var,
+        closure_type,
+        return_type: return_type_var,
+        name: function_symbol,
+        captured_symbols: Vec::new(),
+        recursive: Recursive::NotRecursive,
+        arguments: vec![(
+            state_record_var,
+            AnnotatedMark::known_exhaustive(),
+            Loc::at_zero(Pattern::Identifier(state_arg_symbol)),
+        )],
+        loc_body: Box::new(Loc::at_zero(body)),
+    });
+
+    (finalizer, function_var, decode_err_var)
+}
+
+// Example:
+// initialState : {first: Result a [NoField], second: Result b [NoField]}
+// initialState = {first: Err NoField, second: Err NoField}
+fn initial_state(
+    env: &mut Env<'_>,
+    field_names: &[Lowercase],
+    field_vars: &mut Vec<Variable>,
+    result_field_vars: &mut Vec<Variable>,
+) -> (Variable, Expr) {
+    let mut initial_state_fields = SendMap::default();
+
+    for field_name in field_names {
+        let subs = &mut env.subs;
+        let field_var = subs.fresh_unnamed_flex_var();
+
+        field_vars.push(field_var);
+
+        let no_field_label = "NoField";
+        let union_tags = UnionTags::tag_without_arguments(subs, no_field_label.into());
+        let no_field_var = synth_var(
+            subs,
+            Content::Structure(FlatType::TagUnion(
+                union_tags,
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            )),
+        );
+        let no_field = Expr::Tag {
+            tag_union_var: no_field_var,
+            ext_var: Variable::EMPTY_TAG_UNION,
+            name: no_field_label.into(),
+            arguments: Vec::new(),
+        };
+        let err_label = "Err";
+        let union_tags = UnionTags::for_result(subs, field_var, no_field_var);
+        let result_var = synth_var(
+            subs,
+            Content::Structure(FlatType::TagUnion(
+                union_tags,
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            )),
+        );
+        let field_expr = Expr::Tag {
+            tag_union_var: result_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: err_label.into(),
+            arguments: vec![(no_field_var, Loc::at_zero(no_field))],
+        };
+        result_field_vars.push(result_var);
+        let field = Field {
+            var: result_var,
+            region: Region::zero(),
+            loc_expr: Box::new(Loc::at_zero(field_expr)),
+        };
+
+        initial_state_fields.insert(field_name.clone(), field);
+    }
+
+    let subs = &mut env.subs;
+    let record_field_iter = field_names
+        .iter()
+        .zip(result_field_vars.iter())
+        .map(|(field_name, &var)| (field_name.clone(), RecordField::Required(var)));
+    let flat_type = FlatType::Record(
+        RecordFields::insert_into_subs(subs, record_field_iter),
+        Variable::EMPTY_RECORD,
+    );
+
+    let state_record_var = synth_var(subs, Content::Structure(flat_type));
+
+    (
+        state_record_var,
+        Expr::Record {
+            record_var: state_record_var,
+            fields: initial_state_fields,
+        },
+    )
+}

crates/compiler/derive/src/decoding/tuple.rs

@@ -0,0 +1,994 @@
+use roc_can::expr::{
+    AnnotatedMark, ClosureData, Expr, Field, IntValue, Recursive, WhenBranch, WhenBranchPattern,
+};
+use roc_can::num::{IntBound, IntLitWidth};
+use roc_can::pattern::Pattern;
+use roc_collections::SendMap;
+use roc_module::called_via::CalledVia;
+use roc_module::ident::Lowercase;
+use roc_module::symbol::Symbol;
+use roc_region::all::{Loc, Region};
+use roc_types::subs::{
+    Content, ExhaustiveMark, FlatType, LambdaSet, OptVariable, RecordFields, RedundantMark,
+    SubsSlice, TagExt, TupleElems, UnionLambdas, UnionTags, Variable,
+};
+use roc_types::types::RecordField;
+
+use crate::synth_var;
+use crate::util::{Env, ExtensionKind};
+
+use super::wrap_in_decode_custom_decode_with;
+
+/// Implements decoding of a tuple. For example, for
+///
+/// ```text
+///   (a, b)
+/// ```
+///
+/// we'd like to generate an impl like
+///
+/// ```roc
+/// decoder : Decoder (a, b) fmt | a has Decoding, b has Decoding, fmt has DecoderFormatting
+/// decoder =
+///     initialState : {e0: Result a [NoElem], e1: Result b [NoElem]}
+///     initialState = {e0: Err NoElem, e1: Err NoElem}
+///
+///     stepElem = \state, index ->
+///         when index is
+///             0 ->
+///                 Next (Decode.custom \bytes, fmt ->
+///                     when Decode.decodeWith bytes Decode.decoder fmt is
+///                         {result, rest} ->
+///                             {result: Result.map result \val -> {state & e0: Ok val}, rest})
+///             1 ->
+///                 Next (Decode.custom \bytes, fmt ->
+///                     when Decode.decodeWith bytes Decode.decoder fmt is
+///                         {result, rest} ->
+///                             {result: Result.map result \val -> {state & e1: Ok val}, rest})
+///             _ -> TooLong
+///
+///     finalizer = \st ->
+///         when st.e0 is
+///             Ok e0 ->
+///                 when st.e1 is
+///                     Ok e1 -> Ok (e0, e1)
+///                     Err NoElem -> Err TooShort
+///             Err NoElem -> Err TooShort
+///
+///     Decode.custom \bytes, fmt -> Decode.decodeWith bytes (Decode.tuple initialState stepElem finalizer) fmt
+/// ```
+pub(crate) fn decoder(env: &mut Env, _def_symbol: Symbol, arity: u32) -> (Expr, Variable) {
+    // The decoded type of each index in the tuple, e.g. (a, b).
+    let mut index_vars = Vec::with_capacity(arity as _);
+    // The type of each index in the decoding state, e.g. {e0: Result a [NoElem], e1: Result b [NoElem]}
+    let mut state_fields = Vec::with_capacity(arity as _);
+    let mut state_field_vars = Vec::with_capacity(arity as _);
+
+    // initialState = ...
+    let (state_var, initial_state) = initial_state(
+        env,
+        arity,
+        &mut index_vars,
+        &mut state_fields,
+        &mut state_field_vars,
+    );
+
+    // finalizer = ...
+    let (finalizer, finalizer_var, decode_err_var) = finalizer(
+        env,
+        &index_vars,
+        state_var,
+        &state_fields,
+        &state_field_vars,
+    );
+
+    // stepElem = ...
+    let (step_elem, step_var) = step_elem(
+        env,
+        &index_vars,
+        state_var,
+        &state_fields,
+        &state_field_vars,
+        decode_err_var,
+    );
+
+    // Build up the type of `Decode.tuple` we expect
+    let tuple_decoder_var = env.subs.fresh_unnamed_flex_var();
+    let decode_record_lambda_set = env.subs.fresh_unnamed_flex_var();
+    let decode_record_var = env.import_builtin_symbol_var(Symbol::DECODE_TUPLE);
+    let this_decode_record_var = {
+        let flat_type = FlatType::Func(
+            SubsSlice::insert_into_subs(env.subs, [state_var, step_var, finalizer_var]),
+            decode_record_lambda_set,
+            tuple_decoder_var,
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    env.unify(decode_record_var, this_decode_record_var);
+
+    // Decode.tuple initialState stepElem finalizer
+    let call_decode_record = Expr::Call(
+        Box::new((
+            this_decode_record_var,
+            Loc::at_zero(Expr::AbilityMember(
+                Symbol::DECODE_TUPLE,
+                None,
+                this_decode_record_var,
+            )),
+            decode_record_lambda_set,
+            tuple_decoder_var,
+        )),
+        vec![
+            (state_var, Loc::at_zero(initial_state)),
+            (step_var, Loc::at_zero(step_elem)),
+            (finalizer_var, Loc::at_zero(finalizer)),
+        ],
+        CalledVia::Space,
+    );
+
+    let (call_decode_custom, decode_custom_ret_var) = {
+        let bytes_sym = env.new_symbol("bytes");
+        let fmt_sym = env.new_symbol("fmt");
+        let fmt_var = env.subs.fresh_unnamed_flex_var();
+
+        let (decode_custom, decode_custom_var) = wrap_in_decode_custom_decode_with(
+            env,
+            bytes_sym,
+            (fmt_sym, fmt_var),
+            vec![],
+            (call_decode_record, tuple_decoder_var),
+        );
+
+        (decode_custom, decode_custom_var)
+    };
+
+    (call_decode_custom, decode_custom_ret_var)
+}
+
+// Example:
+// stepElem = \state, index ->
+//     when index is
+//         0 ->
+//             Next (Decode.custom \bytes, fmt ->
+//                 # Uses a single-branch `when` because `let` is more expensive to monomorphize
+//                 # due to checks for polymorphic expressions, and `rec` would be polymorphic.
+//                 when Decode.decodeWith bytes Decode.decoder fmt is
+//                     rec ->
+//                         {
+//                             rest: rec.rest,
+//                             result: when rec.result is
+//                                 Ok val -> Ok {state & e0: Ok val},
+//                                 Err err -> Err err
+//                         })
+//
+//         "e1" ->
+//             Next (Decode.custom \bytes, fmt ->
+//                 when Decode.decodeWith bytes Decode.decoder fmt is
+//                     rec ->
+//                         {
+//                             rest: rec.rest,
+//                             result: when rec.result is
+//                                 Ok val -> Ok {state & e1: Ok val},
+//                                 Err err -> Err err
+//                         })
+//
+//         _ -> TooLong
+fn step_elem(
+    env: &mut Env,
+    index_vars: &[Variable],
+    state_record_var: Variable,
+    state_fields: &[Lowercase],
+    state_field_vars: &[Variable],
+    decode_err_var: Variable,
+) -> (Expr, Variable) {
+    let state_arg_symbol = env.new_symbol("stateRecord");
+    let index_arg_symbol = env.new_symbol("index");
+
+    // +1 because of the default branch.
+    let mut branches = Vec::with_capacity(index_vars.len() + 1);
+    let keep_payload_var = env.subs.fresh_unnamed_flex_var();
+    let keep_or_skip_var = {
+        let keep_payload_subs_slice = SubsSlice::insert_into_subs(env.subs, [keep_payload_var]);
+        let flat_type = FlatType::TagUnion(
+            UnionTags::insert_slices_into_subs(
+                env.subs,
+                [
+                    ("Next".into(), keep_payload_subs_slice),
+                    ("TooLong".into(), Default::default()),
+                ],
+            ),
+            TagExt::Any(Variable::EMPTY_TAG_UNION),
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    for (((index, state_field), &index_var), &result_index_var) in state_fields
+        .iter()
+        .enumerate()
+        .zip(index_vars)
+        .zip(state_field_vars)
+    {
+        // Example:
+        // 0 ->
+        //     Next (Decode.custom \bytes, fmt ->
+        //         when Decode.decodeWith bytes Decode.decoder fmt is
+        //             rec ->
+        //                 {
+        //                     rest: rec.rest,
+        //                     result: when rec.result is
+        //                         Ok val -> Ok {state & e0: Ok val},
+        //                         Err err -> Err err
+        //                 }
+        //     )
+
+        let this_custom_callback_var;
+        let custom_callback_ret_var;
+        let custom_callback = {
+            // \bytes, fmt ->
+            //     when Decode.decodeWith bytes Decode.decoder fmt is
+            //         rec ->
+            //             {
+            //                 rest: rec.rest,
+            //                 result: when rec.result is
+            //                     Ok val -> Ok {state & e0: Ok val},
+            //                     Err err -> Err err
+            //             }
+            let bytes_arg_symbol = env.new_symbol("bytes");
+            let fmt_arg_symbol = env.new_symbol("fmt");
+            let bytes_arg_var = env.subs.fresh_unnamed_flex_var();
+            let fmt_arg_var = env.subs.fresh_unnamed_flex_var();
+
+            // rec.result : [Ok index_var, Err DecodeError]
+            let rec_dot_result = {
+                let tag_union = FlatType::TagUnion(
+                    UnionTags::for_result(env.subs, index_var, decode_err_var),
+                    TagExt::Any(Variable::EMPTY_TAG_UNION),
+                );
+
+                synth_var(env.subs, Content::Structure(tag_union))
+            };
+
+            // rec : { rest: List U8, result: (typeof rec.result) }
+            let rec_var = {
+                let indexs = RecordFields::insert_into_subs(
+                    env.subs,
+                    [
+                        ("rest".into(), RecordField::Required(Variable::LIST_U8)),
+                        ("result".into(), RecordField::Required(rec_dot_result)),
+                    ],
+                );
+                let record = FlatType::Record(indexs, Variable::EMPTY_RECORD);
+
+                synth_var(env.subs, Content::Structure(record))
+            };
+
+            // `Decode.decoder` for the index's value
+            let decoder_var = env.import_builtin_symbol_var(Symbol::DECODE_DECODER);
+            let decode_with_var = env.import_builtin_symbol_var(Symbol::DECODE_DECODE_WITH);
+            let lambda_set_var = env.subs.fresh_unnamed_flex_var();
+            let this_decode_with_var = {
+                let subs_slice = SubsSlice::insert_into_subs(
+                    env.subs,
+                    [bytes_arg_var, decoder_var, fmt_arg_var],
+                );
+                let this_decode_with_var = synth_var(
+                    env.subs,
+                    Content::Structure(FlatType::Func(subs_slice, lambda_set_var, rec_var)),
+                );
+
+                env.unify(decode_with_var, this_decode_with_var);
+
+                this_decode_with_var
+            };
+
+            // The result of decoding this index's value - either the updated state, or a decoding error.
+            let when_expr_var = {
+                let flat_type = FlatType::TagUnion(
+                    UnionTags::for_result(env.subs, state_record_var, decode_err_var),
+                    TagExt::Any(Variable::EMPTY_TAG_UNION),
+                );
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            // What our decoder passed to `Decode.custom` returns - the result of decoding the
+            // index's value, and the remaining bytes.
+            custom_callback_ret_var = {
+                let rest_index = RecordField::Required(Variable::LIST_U8);
+                let result_index = RecordField::Required(when_expr_var);
+                let flat_type = FlatType::Record(
+                    RecordFields::insert_into_subs(
+                        env.subs,
+                        [("rest".into(), rest_index), ("result".into(), result_index)],
+                    ),
+                    Variable::EMPTY_RECORD,
+                );
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            let custom_callback_body = {
+                let rec_symbol = env.new_symbol("rec");
+
+                // # Uses a single-branch `when` because `let` is more expensive to monomorphize
+                // # due to checks for polymorphic expressions, and `rec` would be polymorphic.
+                // when Decode.decodeWith bytes Decode.decoder fmt is
+                //     rec ->
+                //         {
+                //             rest: rec.rest,
+                //             result: when rec.result is
+                //                 Ok val -> Ok {state & e0: Ok val},
+                //                 Err err -> Err err
+                //         }
+                let branch_body = {
+                    let result_val = {
+                        // result: when rec.result is
+                        //     Ok val -> Ok {state & e0: Ok val},
+                        //     Err err -> Err err
+                        let ok_val_symbol = env.new_symbol("val");
+                        let err_val_symbol = env.new_symbol("err");
+                        let ok_branch_expr = {
+                            // Ok {state & e0: Ok val},
+                            let mut updates = SendMap::default();
+
+                            updates.insert(
+                                state_field.clone(),
+                                Field {
+                                    var: result_index_var,
+                                    region: Region::zero(),
+                                    loc_expr: Box::new(Loc::at_zero(Expr::Tag {
+                                        tag_union_var: result_index_var,
+                                        ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                        name: "Ok".into(),
+                                        arguments: vec![(
+                                            index_var,
+                                            Loc::at_zero(Expr::Var(ok_val_symbol, index_var)),
+                                        )],
+                                    })),
+                                },
+                            );
+
+                            let updated_record = Expr::RecordUpdate {
+                                record_var: state_record_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                symbol: state_arg_symbol,
+                                updates,
+                            };
+
+                            Expr::Tag {
+                                tag_union_var: when_expr_var,
+                                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                name: "Ok".into(),
+                                arguments: vec![(state_record_var, Loc::at_zero(updated_record))],
+                            }
+                        };
+
+                        let branches = vec![
+                            // Ok val -> Ok {state & e0: Ok val},
+                            WhenBranch {
+                                patterns: vec![WhenBranchPattern {
+                                    pattern: Loc::at_zero(Pattern::AppliedTag {
+                                        whole_var: rec_dot_result,
+                                        ext_var: Variable::EMPTY_TAG_UNION,
+                                        tag_name: "Ok".into(),
+                                        arguments: vec![(
+                                            index_var,
+                                            Loc::at_zero(Pattern::Identifier(ok_val_symbol)),
+                                        )],
+                                    }),
+                                    degenerate: false,
+                                }],
+                                value: Loc::at_zero(ok_branch_expr),
+                                guard: None,
+                                redundant: RedundantMark::known_non_redundant(),
+                            },
+                            // Err err -> Err err
+                            WhenBranch {
+                                patterns: vec![WhenBranchPattern {
+                                    pattern: Loc::at_zero(Pattern::AppliedTag {
+                                        whole_var: rec_dot_result,
+                                        ext_var: Variable::EMPTY_TAG_UNION,
+                                        tag_name: "Err".into(),
+                                        arguments: vec![(
+                                            decode_err_var,
+                                            Loc::at_zero(Pattern::Identifier(err_val_symbol)),
+                                        )],
+                                    }),
+                                    degenerate: false,
+                                }],
+                                value: Loc::at_zero(Expr::Tag {
+                                    tag_union_var: when_expr_var,
+                                    ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                                    name: "Err".into(),
+                                    arguments: vec![(
+                                        decode_err_var,
+                                        Loc::at_zero(Expr::Var(err_val_symbol, decode_err_var)),
+                                    )],
+                                }),
+                                guard: None,
+                                redundant: RedundantMark::known_non_redundant(),
+                            },
+                        ];
+
+                        // when rec.result is
+                        //     Ok val -> Ok {state & e0: Ok val},
+                        //     Err err -> Err err
+                        Expr::When {
+                            loc_cond: Box::new(Loc::at_zero(Expr::RecordAccess {
+                                record_var: rec_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                field_var: rec_dot_result,
+                                loc_expr: Box::new(Loc::at_zero(Expr::Var(rec_symbol, rec_var))),
+                                field: "result".into(),
+                            })),
+                            cond_var: rec_dot_result,
+                            expr_var: when_expr_var,
+                            region: Region::zero(),
+                            branches,
+                            branches_cond_var: rec_dot_result,
+                            exhaustive: ExhaustiveMark::known_exhaustive(),
+                        }
+                    };
+
+                    // {
+                    //     rest: rec.rest,
+                    //     result: when rec.result is
+                    //         Ok val -> Ok {state & e0: Ok val},
+                    //         Err err -> Err err
+                    // }
+                    let mut fields_map = SendMap::default();
+
+                    fields_map.insert(
+                        "rest".into(),
+                        Field {
+                            var: Variable::LIST_U8,
+                            region: Region::zero(),
+                            loc_expr: Box::new(Loc::at_zero(Expr::RecordAccess {
+                                record_var: rec_var,
+                                ext_var: env.new_ext_var(ExtensionKind::Record),
+                                field_var: Variable::LIST_U8,
+                                loc_expr: Box::new(Loc::at_zero(Expr::Var(rec_symbol, rec_var))),
+                                field: "rest".into(),
+                            })),
+                        },
+                    );
+
+                    // result: when rec.result is
+                    //     Ok val -> Ok {state & e0: Ok val},
+                    //     Err err -> Err err
+                    fields_map.insert(
+                        "result".into(),
+                        Field {
+                            var: when_expr_var,
+                            region: Region::zero(),
+                            loc_expr: Box::new(Loc::at_zero(result_val)),
+                        },
+                    );
+
+                    Expr::Record {
+                        record_var: custom_callback_ret_var,
+                        fields: fields_map,
+                    }
+                };
+
+                let branch = WhenBranch {
+                    patterns: vec![WhenBranchPattern {
+                        pattern: Loc::at_zero(Pattern::Identifier(rec_symbol)),
+                        degenerate: false,
+                    }],
+                    value: Loc::at_zero(branch_body),
+                    guard: None,
+                    redundant: RedundantMark::known_non_redundant(),
+                };
+
+                let condition_expr = Expr::Call(
+                    Box::new((
+                        this_decode_with_var,
+                        Loc::at_zero(Expr::Var(Symbol::DECODE_DECODE_WITH, this_decode_with_var)),
+                        lambda_set_var,
+                        rec_var,
+                    )),
+                    vec![
+                        (
+                            Variable::LIST_U8,
+                            Loc::at_zero(Expr::Var(bytes_arg_symbol, Variable::LIST_U8)),
+                        ),
+                        (
+                            decoder_var,
+                            Loc::at_zero(Expr::AbilityMember(
+                                Symbol::DECODE_DECODER,
+                                None,
+                                decoder_var,
+                            )),
+                        ),
+                        (
+                            fmt_arg_var,
+                            Loc::at_zero(Expr::Var(fmt_arg_symbol, fmt_arg_var)),
+                        ),
+                    ],
+                    CalledVia::Space,
+                );
+
+                // when Decode.decodeWith bytes Decode.decoder fmt is
+                Expr::When {
+                    loc_cond: Box::new(Loc::at_zero(condition_expr)),
+                    cond_var: rec_var,
+                    expr_var: custom_callback_ret_var,
+                    region: Region::zero(),
+                    branches: vec![branch],
+                    branches_cond_var: rec_var,
+                    exhaustive: ExhaustiveMark::known_exhaustive(),
+                }
+            };
+
+            let custom_closure_symbol = env.new_symbol("customCallback");
+            this_custom_callback_var = env.subs.fresh_unnamed_flex_var();
+            let custom_callback_lambda_set_var = {
+                let content = Content::LambdaSet(LambdaSet {
+                    solved: UnionLambdas::insert_into_subs(
+                        env.subs,
+                        [(custom_closure_symbol, [state_record_var])],
+                    ),
+                    recursion_var: OptVariable::NONE,
+                    unspecialized: Default::default(),
+                    ambient_function: this_custom_callback_var,
+                });
+                let custom_callback_lambda_set_var = synth_var(env.subs, content);
+                let subs_slice =
+                    SubsSlice::insert_into_subs(env.subs, [bytes_arg_var, fmt_arg_var]);
+
+                env.subs.set_content(
+                    this_custom_callback_var,
+                    Content::Structure(FlatType::Func(
+                        subs_slice,
+                        custom_callback_lambda_set_var,
+                        custom_callback_ret_var,
+                    )),
+                );
+
+                custom_callback_lambda_set_var
+            };
+
+            // \bytes, fmt -> …
+            Expr::Closure(ClosureData {
+                function_type: this_custom_callback_var,
+                closure_type: custom_callback_lambda_set_var,
+                return_type: custom_callback_ret_var,
+                name: custom_closure_symbol,
+                captured_symbols: vec![(state_arg_symbol, state_record_var)],
+                recursive: Recursive::NotRecursive,
+                arguments: vec![
+                    (
+                        bytes_arg_var,
+                        AnnotatedMark::known_exhaustive(),
+                        Loc::at_zero(Pattern::Identifier(bytes_arg_symbol)),
+                    ),
+                    (
+                        fmt_arg_var,
+                        AnnotatedMark::known_exhaustive(),
+                        Loc::at_zero(Pattern::Identifier(fmt_arg_symbol)),
+                    ),
+                ],
+                loc_body: Box::new(Loc::at_zero(custom_callback_body)),
+            })
+        };
+
+        let decode_custom_ret_var = env.subs.fresh_unnamed_flex_var();
+        let decode_custom = {
+            let decode_custom_var = env.import_builtin_symbol_var(Symbol::DECODE_CUSTOM);
+            let decode_custom_closure_var = env.subs.fresh_unnamed_flex_var();
+            let this_decode_custom_var = {
+                let subs_slice = SubsSlice::insert_into_subs(env.subs, [this_custom_callback_var]);
+                let flat_type =
+                    FlatType::Func(subs_slice, decode_custom_closure_var, decode_custom_ret_var);
+
+                synth_var(env.subs, Content::Structure(flat_type))
+            };
+
+            env.unify(decode_custom_var, this_decode_custom_var);
+
+            // Decode.custom \bytes, fmt -> …
+            Expr::Call(
+                Box::new((
+                    this_decode_custom_var,
+                    Loc::at_zero(Expr::Var(Symbol::DECODE_CUSTOM, this_decode_custom_var)),
+                    decode_custom_closure_var,
+                    decode_custom_ret_var,
+                )),
+                vec![(this_custom_callback_var, Loc::at_zero(custom_callback))],
+                CalledVia::Space,
+            )
+        };
+
+        env.unify(keep_payload_var, decode_custom_ret_var);
+
+        let keep = {
+            // Next (Decode.custom \bytes, fmt ->
+            //     when Decode.decodeWith bytes Decode.decoder fmt is
+            //         rec ->
+            //             {
+            //                 rest: rec.rest,
+            //                 result: when rec.result is
+            //                     Ok val -> Ok {state & e0: Ok val},
+            //                     Err err -> Err err
+            //             }
+            // )
+            Expr::Tag {
+                tag_union_var: keep_or_skip_var,
+                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                name: "Next".into(),
+                arguments: vec![(decode_custom_ret_var, Loc::at_zero(decode_custom))],
+            }
+        };
+
+        let branch = {
+            // 0 ->
+            //     Next (Decode.custom \bytes, fmt ->
+            //         when Decode.decodeWith bytes Decode.decoder fmt is
+            //             rec ->
+            //                 {
+            //                     rest: rec.rest,
+            //                     result: when rec.result is
+            //                         Ok val -> Ok {state & e0: Ok val},
+            //                         Err err -> Err err
+            //                 }
+            //     )
+            WhenBranch {
+                patterns: vec![WhenBranchPattern {
+                    pattern: Loc::at_zero(Pattern::IntLiteral(
+                        Variable::NAT,
+                        Variable::NATURAL,
+                        index.to_string().into_boxed_str(),
+                        IntValue::I128((index as i128).to_ne_bytes()),
+                        IntBound::Exact(IntLitWidth::Nat),
+                    )),
+                    degenerate: false,
+                }],
+                value: Loc::at_zero(keep),
+                guard: None,
+                redundant: RedundantMark::known_non_redundant(),
+            }
+        };
+
+        branches.push(branch);
+    }
+
+    // Example: `_ -> TooLong`
+    let default_branch = WhenBranch {
+        patterns: vec![WhenBranchPattern {
+            pattern: Loc::at_zero(Pattern::Underscore),
+            degenerate: false,
+        }],
+        value: Loc::at_zero(Expr::Tag {
+            tag_union_var: keep_or_skip_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: "TooLong".into(),
+            arguments: Vec::new(),
+        }),
+        guard: None,
+        redundant: RedundantMark::known_non_redundant(),
+    };
+
+    branches.push(default_branch);
+
+    // when index is
+    let body = Expr::When {
+        loc_cond: Box::new(Loc::at_zero(Expr::Var(index_arg_symbol, Variable::NAT))),
+        cond_var: Variable::NAT,
+        expr_var: keep_or_skip_var,
+        region: Region::zero(),
+        branches,
+        branches_cond_var: Variable::NAT,
+        exhaustive: ExhaustiveMark::known_exhaustive(),
+    };
+
+    let step_elem_closure = env.new_symbol("stepElem");
+    let function_type = env.subs.fresh_unnamed_flex_var();
+    let closure_type = {
+        let lambda_set = LambdaSet {
+            solved: UnionLambdas::tag_without_arguments(env.subs, step_elem_closure),
+            recursion_var: OptVariable::NONE,
+            unspecialized: Default::default(),
+            ambient_function: function_type,
+        };
+
+        synth_var(env.subs, Content::LambdaSet(lambda_set))
+    };
+
+    {
+        let args_slice = SubsSlice::insert_into_subs(env.subs, [state_record_var, Variable::NAT]);
+
+        env.subs.set_content(
+            function_type,
+            Content::Structure(FlatType::Func(args_slice, closure_type, keep_or_skip_var)),
+        )
+    };
+
+    let expr = Expr::Closure(ClosureData {
+        function_type,
+        closure_type,
+        return_type: keep_or_skip_var,
+        name: step_elem_closure,
+        captured_symbols: Vec::new(),
+        recursive: Recursive::NotRecursive,
+        arguments: vec![
+            (
+                state_record_var,
+                AnnotatedMark::known_exhaustive(),
+                Loc::at_zero(Pattern::Identifier(state_arg_symbol)),
+            ),
+            (
+                Variable::NAT,
+                AnnotatedMark::known_exhaustive(),
+                Loc::at_zero(Pattern::Identifier(index_arg_symbol)),
+            ),
+        ],
+        loc_body: Box::new(Loc::at_zero(body)),
+    });
+
+    (expr, function_type)
+}
+
+// Example:
+// finalizer = \rec ->
+//     when rec.e0 is
+//         Ok e0 ->
+//             when rec.e1 is
+//                 Ok e1 -> Ok (e0, e1)
+//                 Err NoElem -> Err TooShort
+//         Err NoElem -> Err TooShort
+fn finalizer(
+    env: &mut Env,
+    index_vars: &[Variable],
+    state_record_var: Variable,
+    state_fields: &[Lowercase],
+    state_field_vars: &[Variable],
+) -> (Expr, Variable, Variable) {
+    let state_arg_symbol = env.new_symbol("stateRecord");
+    let mut tuple_elems = Vec::with_capacity(index_vars.len());
+    let mut pattern_symbols = Vec::with_capacity(index_vars.len());
+    let decode_err_var = {
+        let flat_type = FlatType::TagUnion(
+            UnionTags::tag_without_arguments(env.subs, "TooShort".into()),
+            TagExt::Any(Variable::EMPTY_TAG_UNION),
+        );
+
+        synth_var(env.subs, Content::Structure(flat_type))
+    };
+
+    for (i, &index_var) in index_vars.iter().enumerate() {
+        let symbol = env.new_symbol(i);
+
+        pattern_symbols.push(symbol);
+
+        let index_expr = Expr::Var(symbol, index_var);
+
+        tuple_elems.push((index_var, Box::new(Loc::at_zero(index_expr))));
+    }
+
+    // The bottom of the happy path - return the decoded tuple (a, b) wrapped with
+    // "Ok".
+    let return_type_var;
+    let mut body = {
+        let subs = &mut env.subs;
+        let tuple_indices_iter = index_vars.iter().copied().enumerate();
+        let flat_type = FlatType::Tuple(
+            TupleElems::insert_into_subs(subs, tuple_indices_iter),
+            Variable::EMPTY_TUPLE,
+        );
+        let done_tuple_var = synth_var(subs, Content::Structure(flat_type));
+        let done_record = Expr::Tuple {
+            tuple_var: done_tuple_var,
+            elems: tuple_elems,
+        };
+
+        return_type_var = {
+            let flat_type = FlatType::TagUnion(
+                UnionTags::for_result(subs, done_tuple_var, decode_err_var),
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            );
+
+            synth_var(subs, Content::Structure(flat_type))
+        };
+
+        Expr::Tag {
+            tag_union_var: return_type_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: "Ok".into(),
+            arguments: vec![(done_tuple_var, Loc::at_zero(done_record))],
+        }
+    };
+
+    // Unwrap each result in the decoded state
+    //
+    // when rec.e0 is
+    //     Ok e0 -> ...happy path...
+    //     Err NoElem -> Err TooShort
+    for (((symbol, field), &index_var), &result_index_var) in pattern_symbols
+        .iter()
+        .zip(state_fields)
+        .zip(index_vars)
+        .zip(state_field_vars)
+        .rev()
+    {
+        // when rec.e0 is
+        let cond_expr = Expr::RecordAccess {
+            record_var: state_record_var,
+            ext_var: env.new_ext_var(ExtensionKind::Record),
+            field_var: result_index_var,
+            loc_expr: Box::new(Loc::at_zero(Expr::Var(state_arg_symbol, state_record_var))),
+            field: field.clone(),
+        };
+
+        // Example: `Ok x -> expr`
+        let ok_branch = WhenBranch {
+            patterns: vec![WhenBranchPattern {
+                pattern: Loc::at_zero(Pattern::AppliedTag {
+                    whole_var: result_index_var,
+                    ext_var: Variable::EMPTY_TAG_UNION,
+                    tag_name: "Ok".into(),
+                    arguments: vec![(index_var, Loc::at_zero(Pattern::Identifier(*symbol)))],
+                }),
+                degenerate: false,
+            }],
+            value: Loc::at_zero(body),
+            guard: None,
+            redundant: RedundantMark::known_non_redundant(),
+        };
+
+        // Example: `_ -> Err TooShort`
+        let err_branch = WhenBranch {
+            patterns: vec![WhenBranchPattern {
+                pattern: Loc::at_zero(Pattern::Underscore),
+                degenerate: false,
+            }],
+            value: Loc::at_zero(Expr::Tag {
+                tag_union_var: return_type_var,
+                ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+                name: "Err".into(),
+                arguments: vec![(
+                    decode_err_var,
+                    Loc::at_zero(Expr::Tag {
+                        tag_union_var: decode_err_var,
+                        ext_var: Variable::EMPTY_TAG_UNION,
+                        name: "TooShort".into(),
+                        arguments: Vec::new(),
+                    }),
+                )],
+            }),
+            guard: None,
+            redundant: RedundantMark::known_non_redundant(),
+        };
+
+        body = Expr::When {
+            loc_cond: Box::new(Loc::at_zero(cond_expr)),
+            cond_var: result_index_var,
+            expr_var: return_type_var,
+            region: Region::zero(),
+            branches: vec![ok_branch, err_branch],
+            branches_cond_var: result_index_var,
+            exhaustive: ExhaustiveMark::known_exhaustive(),
+        };
+    }
+
+    let function_var = synth_var(env.subs, Content::Error); // We'll fix this up in subs later.
+    let function_symbol = env.new_symbol("finalizer");
+    let lambda_set = LambdaSet {
+        solved: UnionLambdas::tag_without_arguments(env.subs, function_symbol),
+        recursion_var: OptVariable::NONE,
+        unspecialized: Default::default(),
+        ambient_function: function_var,
+    };
+    let closure_type = synth_var(env.subs, Content::LambdaSet(lambda_set));
+    let flat_type = FlatType::Func(
+        SubsSlice::insert_into_subs(env.subs, [state_record_var]),
+        closure_type,
+        return_type_var,
+    );
+
+    // Fix up function_var so it's not Content::Error anymore
+    env.subs
+        .set_content(function_var, Content::Structure(flat_type));
+
+    let finalizer = Expr::Closure(ClosureData {
+        function_type: function_var,
+        closure_type,
+        return_type: return_type_var,
+        name: function_symbol,
+        captured_symbols: Vec::new(),
+        recursive: Recursive::NotRecursive,
+        arguments: vec![(
+            state_record_var,
+            AnnotatedMark::known_exhaustive(),
+            Loc::at_zero(Pattern::Identifier(state_arg_symbol)),
+        )],
+        loc_body: Box::new(Loc::at_zero(body)),
+    });
+
+    (finalizer, function_var, decode_err_var)
+}
+
+// Example:
+// initialState : {e0: Result a [NoElem], e1: Result b [NoElem]}
+// initialState = {e0: Err NoElem, e1: Err NoElem}
+fn initial_state(
+    env: &mut Env<'_>,
+    arity: u32,
+    index_vars: &mut Vec<Variable>,
+    state_fields: &mut Vec<Lowercase>,
+    state_field_vars: &mut Vec<Variable>,
+) -> (Variable, Expr) {
+    let mut initial_state_fields = SendMap::default();
+
+    for i in 0..arity {
+        let subs = &mut env.subs;
+        let index_var = subs.fresh_unnamed_flex_var();
+
+        index_vars.push(index_var);
+
+        let state_field = Lowercase::from(format!("e{i}"));
+        state_fields.push(state_field.clone());
+
+        let no_index_label = "NoElem";
+        let union_tags = UnionTags::tag_without_arguments(subs, no_index_label.into());
+        let no_index_var = synth_var(
+            subs,
+            Content::Structure(FlatType::TagUnion(
+                union_tags,
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            )),
+        );
+        let no_index = Expr::Tag {
+            tag_union_var: no_index_var,
+            ext_var: Variable::EMPTY_TAG_UNION,
+            name: no_index_label.into(),
+            arguments: Vec::new(),
+        };
+        let err_label = "Err";
+        let union_tags = UnionTags::for_result(subs, index_var, no_index_var);
+        let result_var = synth_var(
+            subs,
+            Content::Structure(FlatType::TagUnion(
+                union_tags,
+                TagExt::Any(Variable::EMPTY_TAG_UNION),
+            )),
+        );
+        let index_expr = Expr::Tag {
+            tag_union_var: result_var,
+            ext_var: env.new_ext_var(ExtensionKind::TagUnion),
+            name: err_label.into(),
+            arguments: vec![(no_index_var, Loc::at_zero(no_index))],
+        };
+        state_field_vars.push(result_var);
+        let index = Field {
+            var: result_var,
+            region: Region::zero(),
+            loc_expr: Box::new(Loc::at_zero(index_expr)),
+        };
+
+        initial_state_fields.insert(state_field, index);
+    }
+
+    let subs = &mut env.subs;
+    let record_index_iter = state_fields
+        .iter()
+        .zip(state_field_vars.iter())
+        .map(|(index_name, &var)| (index_name.clone(), RecordField::Required(var)));
+    let flat_type = FlatType::Record(
+        RecordFields::insert_into_subs(subs, record_index_iter),
+        Variable::EMPTY_RECORD,
+    );
+
+    let state_record_var = synth_var(subs, Content::Structure(flat_type));
+
+    (
+        state_record_var,
+        Expr::Record {
+            record_var: state_record_var,
+            fields: initial_state_fields,
+        },
+    )
+}

crates/compiler/derive/src/encoding.rs

@@ -14,7 +14,8 @@ use roc_module::symbol::Symbol;
 use roc_region::all::{Loc, Region};
 use roc_types::subs::{
     Content, ExhaustiveMark, FlatType, GetSubsSlice, LambdaSet, OptVariable, RecordFields,
-    RedundantMark, SubsSlice, TagExt, UnionLambdas, UnionTags, Variable, VariableSubsSlice,
+    RedundantMark, SubsSlice, TagExt, TupleElems, UnionLambdas, UnionTags, Variable,
+    VariableSubsSlice,
 };
 use roc_types::types::RecordField;
 
@@ -50,6 +51,21 @@ pub(crate) fn derive_to_encoder(
 
             to_encoder_record(env, record_var, fields, def_symbol)
         }
+        FlatEncodableKey::Tuple(arity) => {
+            // Generalized tuple var so we can reuse this impl between many tuples:
+            // if arity = n, this is (t1, ..., tn) for fresh t1, ..., tn.
+            let flex_elems = (0..arity)
+                .into_iter()
+                .map(|idx| (idx as usize, env.subs.fresh_unnamed_flex_var()))
+                .collect::<Vec<_>>();
+            let elems = TupleElems::insert_into_subs(env.subs, flex_elems);
+            let tuple_var = synth_var(
+                env.subs,
+                Content::Structure(FlatType::Tuple(elems, Variable::EMPTY_TUPLE)),
+            );
+
+            to_encoder_tuple(env, tuple_var, elems, def_symbol)
+        }
         FlatEncodableKey::TagUnion(tags) => {
             // Generalized tag union var so we can reuse this impl between many unions:
             // if tags = [ A arity=2, B arity=1 ], this is [ A t1 t2, B t3 ] for fresh t1, t2, t3
@@ -490,6 +506,189 @@ fn to_encoder_record(
     (clos, fn_var)
 }
 
+fn to_encoder_tuple(
+    env: &mut Env<'_>,
+    tuple_var: Variable,
+    elems: TupleElems,
+    fn_name: Symbol,
+) -> (Expr, Variable) {
+    // Suppose tup = (t1, t2). Build
+    //
+    // \tup -> Encode.tuple [
+    //      Encode.toEncoder tup.0,
+    //      Encode.toEncoder tup.1,
+    //   ]
+
+    let tup_sym = env.new_symbol("tup");
+    let whole_encoder_in_list_var = env.subs.fresh_unnamed_flex_var(); // type of the encoder in the list
+
+    use Expr::*;
+
+    let elem_encoders_list = elems
+        .iter_all()
+        .map(|(elem_index, elem_var_index)| {
+            let index = env.subs[elem_index];
+            let elem_var = env.subs[elem_var_index];
+            let elem_var_slice = VariableSubsSlice::new(elem_var_index.index, 1);
+
+            // tup.0
+            let tuple_access = TupleAccess {
+                tuple_var,
+                ext_var: env.subs.fresh_unnamed_flex_var(),
+                elem_var,
+                loc_expr: Box::new(Loc::at_zero(Var(
+                    tup_sym,
+                    env.subs.fresh_unnamed_flex_var(),
+                ))),
+                index,
+            };
+
+            // build `toEncoder tup.0` type
+            // val -[uls]-> Encoder fmt | fmt has EncoderFormatting
+            let to_encoder_fn_var = env.import_builtin_symbol_var(Symbol::ENCODE_TO_ENCODER);
+
+            // (typeof tup.0) -[clos]-> t1
+            let to_encoder_clos_var = env.subs.fresh_unnamed_flex_var(); // clos
+            let encoder_var = env.subs.fresh_unnamed_flex_var(); // t1
+            let this_to_encoder_fn_var = synth_var(
+                env.subs,
+                Content::Structure(FlatType::Func(
+                    elem_var_slice,
+                    to_encoder_clos_var,
+                    encoder_var,
+                )),
+            );
+
+            //   val            -[uls]->  Encoder fmt | fmt has EncoderFormatting
+            // ~ (typeof tup.0) -[clos]-> t1
+            env.unify(to_encoder_fn_var, this_to_encoder_fn_var);
+
+            // toEncoder : (typeof tup.0) -[clos]-> Encoder fmt | fmt has EncoderFormatting
+            let to_encoder_var = AbilityMember(Symbol::ENCODE_TO_ENCODER, None, to_encoder_fn_var);
+            let to_encoder_fn = Box::new((
+                to_encoder_fn_var,
+                Loc::at_zero(to_encoder_var),
+                to_encoder_clos_var,
+                encoder_var,
+            ));
+
+            // toEncoder tup.0
+            let to_encoder_call = Call(
+                to_encoder_fn,
+                vec![(elem_var, Loc::at_zero(tuple_access))],
+                CalledVia::Space,
+            );
+
+            // NOTE: must be done to unify the lambda sets under `encoder_var`
+            env.unify(encoder_var, whole_encoder_in_list_var);
+
+            Loc::at_zero(to_encoder_call)
+        })
+        .collect::<Vec<_>>();
+
+    // typeof [ toEncoder tup.0, toEncoder tup.1 ]
+    let whole_encoder_in_list_var_slice =
+        VariableSubsSlice::insert_into_subs(env.subs, once(whole_encoder_in_list_var));
+    let elem_encoders_list_var = synth_var(
+        env.subs,
+        Content::Structure(FlatType::Apply(
+            Symbol::LIST_LIST,
+            whole_encoder_in_list_var_slice,
+        )),
+    );
+
+    // [ toEncoder tup.0, toEncoder tup.1 ]
+    let elem_encoders_list = List {
+        elem_var: whole_encoder_in_list_var,
+        loc_elems: elem_encoders_list,
+    };
+
+    // build `Encode.tuple [ toEncoder tup.0, toEncoder tup.1 ]` type
+    // List (Encoder fmt) -[uls]-> Encoder fmt | fmt has EncoderFormatting
+    let encode_tuple_fn_var = env.import_builtin_symbol_var(Symbol::ENCODE_TUPLE);
+
+    // elem_encoders_list_var -[clos]-> t1
+    let elem_encoders_list_var_slice =
+        VariableSubsSlice::insert_into_subs(env.subs, once(elem_encoders_list_var));
+    let encode_tuple_clos_var = env.subs.fresh_unnamed_flex_var(); // clos
+    let encoder_var = env.subs.fresh_unnamed_flex_var(); // t1
+    let this_encode_tuple_fn_var = synth_var(
+        env.subs,
+        Content::Structure(FlatType::Func(
+            elem_encoders_list_var_slice,
+            encode_tuple_clos_var,
+            encoder_var,
+        )),
+    );
+
+    //   List (Encoder fmt)     -[uls]->  Encoder fmt | fmt has EncoderFormatting
+    // ~ elem_encoders_list_var -[clos]-> t1
+    env.unify(encode_tuple_fn_var, this_encode_tuple_fn_var);
+
+    // Encode.tuple : elem_encoders_list_var -[clos]-> Encoder fmt | fmt has EncoderFormatting
+    let encode_tuple_var = AbilityMember(Symbol::ENCODE_TUPLE, None, encode_tuple_fn_var);
+    let encode_tuple_fn = Box::new((
+        encode_tuple_fn_var,
+        Loc::at_zero(encode_tuple_var),
+        encode_tuple_clos_var,
+        encoder_var,
+    ));
+
+    // Encode.tuple [ { key: .., value: .. }, .. ]
+    let encode_tuple_call = Call(
+        encode_tuple_fn,
+        vec![(elem_encoders_list_var, Loc::at_zero(elem_encoders_list))],
+        CalledVia::Space,
+    );
+
+    // Encode.custom \bytes, fmt -> Encode.appendWith bytes (Encode.tuple_var ..) fmt
+    let (body, this_encoder_var) =
+        wrap_in_encode_custom(env, encode_tuple_call, encoder_var, tup_sym, tuple_var);
+
+    // Create fn_var for ambient capture; we fix it up below.
+    let fn_var = synth_var(env.subs, Content::Error);
+
+    // -[fn_name]->
+    let fn_name_labels = UnionLambdas::insert_into_subs(env.subs, once((fn_name, vec![])));
+    let fn_clos_var = synth_var(
+        env.subs,
+        Content::LambdaSet(LambdaSet {
+            solved: fn_name_labels,
+            recursion_var: OptVariable::NONE,
+            unspecialized: SubsSlice::default(),
+            ambient_function: fn_var,
+        }),
+    );
+    // typeof tup -[fn_name]-> (typeof Encode.tuple [ .. ] = Encoder fmt)
+    let tuple_var_slice = SubsSlice::insert_into_subs(env.subs, once(tuple_var));
+    env.subs.set_content(
+        fn_var,
+        Content::Structure(FlatType::Func(
+            tuple_var_slice,
+            fn_clos_var,
+            this_encoder_var,
+        )),
+    );
+
+    // \tup -[fn_name]-> Encode.tuple [ { key: .., value: .. }, .. ]
+    let clos = Closure(ClosureData {
+        function_type: fn_var,
+        closure_type: fn_clos_var,
+        return_type: this_encoder_var,
+        name: fn_name,
+        captured_symbols: vec![],
+        recursive: Recursive::NotRecursive,
+        arguments: vec![(
+            tuple_var,
+            AnnotatedMark::known_exhaustive(),
+            Loc::at_zero(Pattern::Identifier(tup_sym)),
+        )],
+        loc_body: Box::new(Loc::at_zero(body)),
+    });
+
+    (clos, fn_var)
+}
+
 fn to_encoder_tag_union(
     env: &mut Env<'_>,
     tag_union_var: Variable,

crates/compiler/derive/src/hash.rs

@@ -19,8 +19,8 @@ use roc_types::{
     num::int_lit_width_to_variable,
     subs::{
         Content, ExhaustiveMark, FlatType, GetSubsSlice, LambdaSet, OptVariable, RecordFields,
-        RedundantMark, Subs, SubsIndex, SubsSlice, TagExt, UnionLambdas, UnionTags, Variable,
-        VariableSubsSlice,
+        RedundantMark, Subs, SubsIndex, SubsSlice, TagExt, TupleElems, UnionLambdas, UnionTags,
+        Variable, VariableSubsSlice,
     },
     types::RecordField,
 };
@@ -30,6 +30,7 @@ use crate::{synth_var, util::Env, DerivedBody};
 pub(crate) fn derive_hash(env: &mut Env<'_>, key: FlatHashKey, def_symbol: Symbol) -> DerivedBody {
     let (body_type, body) = match key {
         FlatHashKey::Record(fields) => hash_record(env, def_symbol, fields),
+        FlatHashKey::Tuple(arity) => hash_tuple(env, def_symbol, arity),
         FlatHashKey::TagUnion(tags) => {
             if tags.len() == 1 {
                 hash_newtype_tag_union(env, def_symbol, tags.into_iter().next().unwrap())
@@ -122,6 +123,76 @@ fn hash_record(env: &mut Env<'_>, fn_name: Symbol, fields: Vec<Lowercase>) -> (V
     )
 }
 
+fn hash_tuple(env: &mut Env<'_>, fn_name: Symbol, arity: u32) -> (Variable, Expr) {
+    // Suppose tup = (v1, ..., vn).
+    // Build a generalized type t_tup = (t1, ..., tn), with fresh t1, ..., tn,
+    // so that we can re-use the derived impl for many tuples of the same arity.
+    let (tuple_var, tuple_elems) = {
+        // TODO: avoid an allocation here by pre-allocating the indices and variables `TupleElems`
+        // will be instantiated with.
+        let flex_elems: Vec<_> = (0..arity)
+            .into_iter()
+            .map(|i| (i as usize, env.subs.fresh_unnamed_flex_var()))
+            .collect();
+        let elems = TupleElems::insert_into_subs(env.subs, flex_elems);
+        let tuple_var = synth_var(
+            env.subs,
+            Content::Structure(FlatType::Tuple(elems, Variable::EMPTY_TUPLE)),
+        );
+
+        (tuple_var, elems)
+    };
+
+    // Now, a hasher for this tuple is
+    //
+    // hash_tup : hasher, (t1, ..., tn) -> hasher | hasher has Hasher
+    // hash_tup = \hasher, tup ->
+    //   Hash.hash (
+    //      Hash.hash
+    //          ...
+    //          (Hash.hash hasher tup.0)
+    //          ...
+    //      tup.n1)
+    //   tup.n
+    //
+    // So, just a build a fold travelling up the elements.
+    let tup_sym = env.new_symbol("tup");
+
+    let hasher_sym = env.new_symbol("hasher");
+    let hasher_var = synth_var(env.subs, Content::FlexAbleVar(None, Subs::AB_HASHER));
+
+    let (body_var, body) = tuple_elems.iter_all().fold(
+        (hasher_var, Expr::Var(hasher_sym, hasher_var)),
+        |total_hasher, (elem_idx, elem_var)| {
+            let index = env.subs[elem_idx];
+            let elem_var = env.subs[elem_var];
+
+            let elem_access = Expr::TupleAccess {
+                tuple_var,
+                elem_var,
+                ext_var: env.subs.fresh_unnamed_flex_var(),
+                loc_expr: Box::new(Loc::at_zero(Expr::Var(
+                    tup_sym,
+                    env.subs.fresh_unnamed_flex_var(),
+                ))),
+                index,
+            };
+
+            call_hash_hash(env, total_hasher, (elem_var, elem_access))
+        },
+    );
+
+    // Finally, build the closure
+    // \hasher, rcd -> body
+    build_outer_derived_closure(
+        env,
+        fn_name,
+        (hasher_var, hasher_sym),
+        (tuple_var, Pattern::Identifier(tup_sym)),
+        (body_var, body),
+    )
+}
+
 /// Build a `hash` implementation for a non-singleton tag union.
 fn hash_tag_union(
     env: &mut Env<'_>,

crates/compiler/derive/src/util.rs

@@ -18,19 +18,20 @@ pub(crate) struct Env<'a> {
 }
 
 impl Env<'_> {
-    pub fn new_symbol(&mut self, name_hint: &str) -> Symbol {
+    pub fn new_symbol(&mut self, name_hint: impl std::string::ToString) -> Symbol {
         if cfg!(any(
             debug_assertions,
             test,
             feature = "debug-derived-symbols"
         )) {
             let mut i = 0;
+            let hint = name_hint.to_string();
             let debug_name = loop {
                 i += 1;
                 let name = if i == 1 {
-                    name_hint.to_owned()
+                    hint.clone()
                 } else {
-                    format!("{}{}", name_hint, i)
+                    format!("{}{}", hint, i)
                 };
                 if self.derived_ident_ids.get_id(&name).is_none() {
                     break name;

crates/compiler/derive_key/src/decoding.rs

@@ -2,7 +2,7 @@ use roc_module::{ident::Lowercase, symbol::Symbol};
 use roc_types::subs::{Content, FlatType, Subs, Variable};
 
 use crate::{
-    util::{check_derivable_ext_var, debug_name_record},
+    util::{check_derivable_ext_var, debug_name_record, debug_name_tuple},
     DeriveError,
 };
 
@@ -18,6 +18,7 @@ pub enum FlatDecodableKey {
 
     // Unfortunate that we must allocate here, c'est la vie
     Record(Vec<Lowercase>),
+    Tuple(u32),
 }
 
 impl FlatDecodableKey {
@@ -25,6 +26,7 @@ impl FlatDecodableKey {
         match self {
             FlatDecodableKey::List() => "list".to_string(),
             FlatDecodableKey::Record(fields) => debug_name_record(fields),
+            FlatDecodableKey::Tuple(arity) => debug_name_tuple(*arity),
         }
     }
 }
@@ -61,8 +63,14 @@ impl FlatDecodable {
 
                     Ok(Key(FlatDecodableKey::Record(field_names)))
                 }
-                FlatType::Tuple(_elems, _ext) => {
-                    todo!()
+                FlatType::Tuple(elems, ext) => {
+                    let (elems_iter, ext) = elems.sorted_iterator_and_ext(subs, ext);
+
+                    check_derivable_ext_var(subs, ext, |ext| {
+                        matches!(ext, Content::Structure(FlatType::EmptyTuple))
+                    })?;
+
+                    Ok(Key(FlatDecodableKey::Tuple(elems_iter.count() as _)))
                 }
                 FlatType::TagUnion(_tags, _ext) | FlatType::RecursiveTagUnion(_, _tags, _ext) => {
                     Err(Underivable) // yet

crates/compiler/derive_key/src/encoding.rs

@@ -5,7 +5,7 @@ use roc_module::{
 use roc_types::subs::{Content, FlatType, GetSubsSlice, Subs, Variable};
 
 use crate::{
-    util::{check_derivable_ext_var, debug_name_record, debug_name_tag},
+    util::{check_derivable_ext_var, debug_name_record, debug_name_tag, debug_name_tuple},
     DeriveError,
 };
 
@@ -22,6 +22,7 @@ pub enum FlatEncodableKey {
     Dict(/* takes two variables */),
     // Unfortunate that we must allocate here, c'est la vie
     Record(Vec<Lowercase>),
+    Tuple(u32),
     TagUnion(Vec<(TagName, u16)>),
 }
 
@@ -32,6 +33,7 @@ impl FlatEncodableKey {
             FlatEncodableKey::Set() => "set".to_string(),
             FlatEncodableKey::Dict() => "dict".to_string(),
             FlatEncodableKey::Record(fields) => debug_name_record(fields),
+            FlatEncodableKey::Tuple(arity) => debug_name_tuple(*arity),
             FlatEncodableKey::TagUnion(tags) => debug_name_tag(tags),
         }
     }
@@ -66,8 +68,14 @@ impl FlatEncodable {
 
                     Ok(Key(FlatEncodableKey::Record(field_names)))
                 }
-                FlatType::Tuple(_elems, _ext) => {
-                    todo!()
+                FlatType::Tuple(elems, ext) => {
+                    let (elems_iter, ext) = elems.sorted_iterator_and_ext(subs, ext);
+
+                    check_derivable_ext_var(subs, ext, |ext| {
+                        matches!(ext, Content::Structure(FlatType::EmptyTuple))
+                    })?;
+
+                    Ok(Key(FlatEncodableKey::Tuple(elems_iter.count() as _)))
                 }
                 FlatType::TagUnion(tags, ext) | FlatType::RecursiveTagUnion(_, tags, ext) => {
                     // The recursion var doesn't matter, because the derived implementation will only

crates/compiler/derive_key/src/hash.rs

@@ -5,7 +5,7 @@ use roc_module::{
 use roc_types::subs::{Content, FlatType, GetSubsSlice, Subs, Variable};
 
 use crate::{
-    util::{check_derivable_ext_var, debug_name_record, debug_name_tag},
+    util::{check_derivable_ext_var, debug_name_record, debug_name_tag, debug_name_tuple},
     DeriveError,
 };
 
@@ -21,6 +21,7 @@ pub enum FlatHash {
 pub enum FlatHashKey {
     // Unfortunate that we must allocate here, c'est la vie
     Record(Vec<Lowercase>),
+    Tuple(u32),
     TagUnion(Vec<(TagName, u16)>),
 }
 
@@ -28,6 +29,7 @@ impl FlatHashKey {
     pub(crate) fn debug_name(&self) -> String {
         match self {
             FlatHashKey::Record(fields) => debug_name_record(fields),
+            FlatHashKey::Tuple(arity) => debug_name_tuple(*arity),
             FlatHashKey::TagUnion(tags) => debug_name_tag(tags),
         }
     }
@@ -65,8 +67,14 @@ impl FlatHash {
 
                     Ok(Key(FlatHashKey::Record(field_names)))
                 }
-                FlatType::Tuple(_elems, _ext) => {
-                    todo!();
+                FlatType::Tuple(elems, ext) => {
+                    let (elems_iter, ext) = elems.sorted_iterator_and_ext(subs, ext);
+
+                    check_derivable_ext_var(subs, ext, |ext| {
+                        matches!(ext, Content::Structure(FlatType::EmptyTuple))
+                    })?;
+
+                    Ok(Key(FlatHashKey::Tuple(elems_iter.count() as _)))
                 }
                 FlatType::TagUnion(tags, ext) | FlatType::RecursiveTagUnion(_, tags, ext) => {
                     // The recursion var doesn't matter, because the derived implementation will only

crates/compiler/derive_key/src/util.rs

@@ -43,6 +43,10 @@ pub(crate) fn debug_name_record(fields: &[Lowercase]) -> String {
     str
 }
 
+pub(crate) fn debug_name_tuple(arity: u32) -> String {
+    format!("(arity:{arity})")
+}
+
 pub(crate) fn debug_name_tag(tags: &[(TagName, u16)]) -> String {
     let mut str = String::from('[');
     tags.iter().enumerate().for_each(|(i, (tag, arity))| {

crates/compiler/module/src/symbol.rs

@@ -1500,11 +1500,12 @@ define_builtins! {
         18 ENCODE_STRING: "string"
         19 ENCODE_LIST: "list"
         20 ENCODE_RECORD: "record"
-        21 ENCODE_TAG: "tag"
-        22 ENCODE_CUSTOM: "custom"
-        23 ENCODE_APPEND_WITH: "appendWith"
-        24 ENCODE_APPEND: "append"
-        25 ENCODE_TO_BYTES: "toBytes"
+        21 ENCODE_TUPLE: "tuple"
+        22 ENCODE_TAG: "tag"
+        23 ENCODE_CUSTOM: "custom"
+        24 ENCODE_APPEND_WITH: "appendWith"
+        25 ENCODE_APPEND: "append"
+        26 ENCODE_TO_BYTES: "toBytes"
     }
     12 DECODE: "Decode" => {
         0 DECODE_DECODE_ERROR: "DecodeError" exposed_type=true
@@ -1530,11 +1531,12 @@ define_builtins! {
         20 DECODE_STRING: "string"
         21 DECODE_LIST: "list"
         22 DECODE_RECORD: "record"
-        23 DECODE_CUSTOM: "custom"
-        24 DECODE_DECODE_WITH: "decodeWith"
-        25 DECODE_FROM_BYTES_PARTIAL: "fromBytesPartial"
-        26 DECODE_FROM_BYTES: "fromBytes"
-        27 DECODE_MAP_RESULT: "mapResult"
+        23 DECODE_TUPLE: "tuple"
+        24 DECODE_CUSTOM: "custom"
+        25 DECODE_DECODE_WITH: "decodeWith"
+        26 DECODE_FROM_BYTES_PARTIAL: "fromBytesPartial"
+        27 DECODE_FROM_BYTES: "fromBytes"
+        28 DECODE_MAP_RESULT: "mapResult"
     }
     13 HASH: "Hash" => {
         0 HASH_HASH_ABILITY: "Hash" exposed_type=true

crates/compiler/solve/src/ability.rs

@@ -881,6 +881,15 @@ impl DerivableVisitor for DeriveEncoding {
         Ok(Descend(true))
     }
 
+    #[inline(always)]
+    fn visit_tuple(
+        _subs: &Subs,
+        _var: Variable,
+        _elems: TupleElems,
+    ) -> Result<Descend, NotDerivable> {
+        Ok(Descend(true))
+    }
+
     #[inline(always)]
     fn visit_tag_union(_var: Variable) -> Result<Descend, NotDerivable> {
         Ok(Descend(true))
@@ -988,6 +997,15 @@ impl DerivableVisitor for DeriveDecoding {
         Ok(Descend(true))
     }
 
+    #[inline(always)]
+    fn visit_tuple(
+        _subs: &Subs,
+        _var: Variable,
+        _elems: TupleElems,
+    ) -> Result<Descend, NotDerivable> {
+        Ok(Descend(true))
+    }
+
     #[inline(always)]
     fn visit_tag_union(_var: Variable) -> Result<Descend, NotDerivable> {
         Ok(Descend(true))
@@ -1094,6 +1112,15 @@ impl DerivableVisitor for DeriveHash {
         Ok(Descend(true))
     }
 
+    #[inline(always)]
+    fn visit_tuple(
+        _subs: &Subs,
+        _var: Variable,
+        _elems: TupleElems,
+    ) -> Result<Descend, NotDerivable> {
+        Ok(Descend(true))
+    }
+
     #[inline(always)]
     fn visit_tag_union(_var: Variable) -> Result<Descend, NotDerivable> {
         Ok(Descend(true))
@@ -1200,6 +1227,15 @@ impl DerivableVisitor for DeriveEq {
         Ok(Descend(true))
     }
 
+    #[inline(always)]
+    fn visit_tuple(
+        _subs: &Subs,
+        _var: Variable,
+        _elems: TupleElems,
+    ) -> Result<Descend, NotDerivable> {
+        Ok(Descend(true))
+    }
+
     #[inline(always)]
     fn visit_tag_union(_var: Variable) -> Result<Descend, NotDerivable> {
         Ok(Descend(true))

crates/compiler/solve/src/specialize.rs

@@ -748,7 +748,7 @@ fn get_specialization_lambda_set_ambient_function<P: Phase>(
                                 let specialized_lambda_set = *specialization
                                     .specialization_lambda_sets
                                     .get(&lset_region)
-                                    .expect("lambda set region not resolved");
+                                    .unwrap_or_else(|| panic!("lambda set region not resolved: {:?}", (spec_symbol, specialization)));
                                 Ok(specialized_lambda_set)
                             }
                             MemberImpl::Error => todo_abilities!(),

crates/compiler/test_derive/src/decoding.rs

@@ -28,6 +28,11 @@ test_key_eq! {
     explicit_empty_record_and_implicit_empty_record:
         v!(EMPTY_RECORD), v!({})
 
+    same_tuple:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16),))
+    same_tuple_fields_diff_types:
+        v!((v!(U8), v!(U16),)), v!((v!(U32), v!(U64),))
+
     list_list_diff_types:
         v!(Symbol::LIST_LIST v!(STR)), v!(Symbol::LIST_LIST v!(U8))
     str_str:
@@ -41,6 +46,9 @@ test_key_neq! {
         v!({ a: v!(U8), }), v!({ b: v!(U8), })
     record_empty_vs_nonempty:
         v!(EMPTY_RECORD), v!({ a: v!(U8), })
+
+    different_tuple_arities:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16), v!(U32),))
 }
 
 #[test]
@@ -167,3 +175,59 @@ fn record_2_fields() {
         )
     })
 }
+
+#[test]
+fn tuple_2_fields() {
+    derive_test(Decoder, v!((v!(STR), v!(U8),)), |golden| {
+        assert_snapshot!(golden, @r###"
+        # derived for ( Str, U8 )*
+        # Decoder ( val, val1 )* fmt | fmt has DecoderFormatting, val has Decoding, val1 has Decoding
+        # List U8, fmt -[[custom(22)]]-> { rest : List U8, result : [Err [TooShort], Ok ( val, val1 )a] } | fmt has DecoderFormatting, val has Decoding, val1 has Decoding
+        # Specialization lambda sets:
+        #   @<1>: [[custom(22)]]
+        #Derived.decoder_(arity:2) =
+          custom
+            \#Derived.bytes3, #Derived.fmt3 ->
+              decodeWith
+                #Derived.bytes3
+                (tuple
+                  { e1: Err NoElem, e0: Err NoElem }
+                  \#Derived.stateRecord2, #Derived.index ->
+                    when #Derived.index is
+                      0 ->
+                        Next (custom
+                          \#Derived.bytes, #Derived.fmt ->
+                            when decodeWith #Derived.bytes decoder #Derived.fmt is
+                              #Derived.rec ->
+                                {
+                                  result: when #Derived.rec.result is
+                                      Ok #Derived.val ->
+                                        Ok { stateRecord2 & e0: Ok #Derived.val }
+                                      Err #Derived.err -> Err #Derived.err,
+                                  rest: #Derived.rec.rest
+                                })
+                      1 ->
+                        Next (custom
+                          \#Derived.bytes2, #Derived.fmt2 ->
+                            when decodeWith #Derived.bytes2 decoder #Derived.fmt2 is
+                              #Derived.rec2 ->
+                                {
+                                  result: when #Derived.rec2.result is
+                                      Ok #Derived.val2 ->
+                                        Ok { stateRecord2 & e1: Ok #Derived.val2 }
+                                      Err #Derived.err2 -> Err #Derived.err2,
+                                  rest: #Derived.rec2.rest
+                                })
+                      _ -> TooLong
+                  \#Derived.stateRecord ->
+                    when #Derived.stateRecord.e0 is
+                      Ok #Derived.0 ->
+                        when #Derived.stateRecord.e1 is
+                          Ok #Derived.1 -> Ok ( #Derived.0, #Derived.1 )
+                          _ -> Err TooShort
+                      _ -> Err TooShort)
+                #Derived.fmt3
+        "###
+        )
+    })
+}

crates/compiler/test_derive/src/encoding.rs

@@ -33,6 +33,11 @@ test_key_eq! {
         v!({ a: v!(U8), b: v!(U8), }),
         v!({ ?a: v!(U8), ?b: v!(U8), })
 
+    same_tuple:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16),))
+    same_tuple_fields_diff_types:
+        v!((v!(U8), v!(U16),)), v!((v!(U32), v!(U64),))
+
     same_tag_union:
         v!([ A v!(U8) v!(STR), B v!(STR) ]), v!([ A v!(U8) v!(STR), B v!(STR) ])
     same_tag_union_tags_diff_types:
@@ -78,6 +83,9 @@ test_key_neq! {
     record_empty_vs_nonempty:
         v!(EMPTY_RECORD), v!({ a: v!(U8), })
 
+    different_tuple_arities:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16), v!(U32),))
+
     different_tag_union_tags:
         v!([ A v!(U8) ]), v!([ B v!(U8) ])
     tag_union_empty_vs_nonempty:
@@ -265,6 +273,29 @@ fn two_field_record() {
     })
 }
 
+#[test]
+fn two_field_tuple() {
+    derive_test(ToEncoder, v!((v!(U8), v!(STR),)), |golden| {
+        assert_snapshot!(golden, @r###"
+        # derived for ( U8, Str )*
+        # ( val, val1 )* -[[toEncoder_(arity:2)(0)]]-> Encoder fmt | fmt has EncoderFormatting, val has Encoding, val1 has Encoding
+        # ( val, val1 )a -[[toEncoder_(arity:2)(0)]]-> (List U8, fmt -[[custom(2) ( val, val1 )a]]-> List U8) | fmt has EncoderFormatting, val has Encoding, val1 has Encoding
+        # Specialization lambda sets:
+        #   @<1>: [[toEncoder_(arity:2)(0)]]
+        #   @<2>: [[custom(2) ( val, val1 )*]] | val has Encoding, val1 has Encoding
+        #Derived.toEncoder_(arity:2) =
+          \#Derived.tup ->
+            custom
+              \#Derived.bytes, #Derived.fmt ->
+                appendWith
+                  #Derived.bytes
+                  (tuple [toEncoder #Derived.tup.0, toEncoder #Derived.tup.1])
+                  #Derived.fmt
+        "###
+        )
+    })
+}
+
 #[test]
 #[ignore = "NOTE: this would never actually happen, because [] is uninhabited, and hence toEncoder can never be called with a value of []!
 Rightfully it induces broken assertions in other parts of the compiler, so we ignore it."]

crates/compiler/test_derive/src/hash.rs

@@ -28,6 +28,11 @@ test_key_eq! {
     explicit_empty_record_and_implicit_empty_record:
         v!(EMPTY_RECORD), v!({})
 
+    same_tuple:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16),))
+    same_tuple_fields_diff_types:
+        v!((v!(U8), v!(U16),)), v!((v!(U32), v!(U64),))
+
     same_tag_union:
         v!([ A v!(U8) v!(STR), B v!(STR) ]), v!([ A v!(U8) v!(STR), B v!(STR) ])
     same_tag_union_tags_diff_types:
@@ -51,6 +56,9 @@ test_key_neq! {
     record_empty_vs_nonempty:
         v!(EMPTY_RECORD), v!({ a: v!(U8), })
 
+    different_tuple_arities:
+        v!((v!(U8), v!(U16),)), v!((v!(U8), v!(U16), v!(U32),))
+
     different_tag_union_tags:
         v!([ A v!(U8) ]), v!([ B v!(U8) ])
     tag_union_empty_vs_nonempty:
@@ -201,6 +209,23 @@ fn two_field_record() {
     })
 }
 
+#[test]
+fn two_element_tuple() {
+    derive_test(Hash, v!((v!(U8), v!(STR),)), |golden| {
+        assert_snapshot!(golden, @r###"
+        # derived for ( U8, Str )*
+        # hasher, ( a, a1 )* -[[hash_(arity:2)(0)]]-> hasher | a has Hash, a1 has Hash, hasher has Hasher
+        # hasher, ( a, a1 )* -[[hash_(arity:2)(0)]]-> hasher | a has Hash, a1 has Hash, hasher has Hasher
+        # Specialization lambda sets:
+        #   @<1>: [[hash_(arity:2)(0)]]
+        #Derived.hash_(arity:2) =
+          \#Derived.hasher, #Derived.tup ->
+            hash (hash #Derived.hasher #Derived.tup.0) #Derived.tup.1
+        "###
+        )
+    })
+}
+
 #[test]
 fn tag_one_label_no_payloads() {
     derive_test(Hash, v!([A]), |golden| {

crates/compiler/test_derive/src/util.rs

@@ -89,6 +89,22 @@ macro_rules! v {
              roc_derive::synth_var(subs, Content::Structure(FlatType::Record(fields, ext)))
          }
      }};
+     (( $($make_v:expr,)* )$( $($ext:tt)+ )?) => {{
+         #[allow(unused)]
+         use roc_types::subs::{Subs, RecordFields, Content, FlatType, Variable, TupleElems};
+         |subs: &mut Subs| {
+             let elems = [
+                 $($make_v(subs),)*
+             ].into_iter().enumerate();
+             let elems = TupleElems::insert_into_subs(subs, elems);
+
+             #[allow(unused_mut, unused)]
+             let mut ext = Variable::EMPTY_TUPLE;
+             $( ext = $crate::v!($($ext)+)(subs); )?
+
+             roc_derive::synth_var(subs, Content::Structure(FlatType::Tuple(elems, ext)))
+         }
+     }};
      ([ $($tag:ident $($payload:expr)*),* ] as $rec_var:ident) => {{
          use roc_types::subs::{Subs, SubsIndex, Variable, Content, FlatType, TagExt, UnionTags};
          use roc_module::ident::TagName;

crates/compiler/test_gen/src/gen_abilities.rs

@@ -825,6 +825,52 @@ fn encode_derived_record_with_many_types() {
     )
 }
 
+#[test]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+fn encode_derived_tuple_two_fields() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            app "test"
+                imports [Encode, Json]
+                provides [main] to "./platform"
+
+            main =
+                tup = ("foo", 10u8)
+                result = Str.fromUtf8 (Encode.toBytes tup Json.toUtf8)
+                when result is
+                    Ok s -> s
+                    _ -> "<bad>"
+            "#
+        ),
+        RocStr::from(r#"["foo",10]"#),
+        RocStr
+    )
+}
+
+#[test]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+fn encode_derived_tuple_of_tuples() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            app "test"
+                imports [Encode, Json]
+                provides [main] to "./platform"
+
+            main =
+                tup = ( ("foo", 10u8), (23u8, "bar", 15u8) )
+                result = Str.fromUtf8 (Encode.toBytes tup Json.toUtf8)
+                when result is
+                    Ok s -> s
+                    _ -> "<bad>"
+            "#
+        ),
+        RocStr::from(r#"[["foo",10],[23,"bar",15]]"#),
+        RocStr
+    )
+}
+
 #[test]
 #[cfg(all(any(feature = "gen-llvm", feature = "gen-wasm")))]
 fn encode_derived_generic_record_with_different_field_types() {
@@ -1312,6 +1358,50 @@ fn decode_record_of_record() {
     )
 }
 
+#[test]
+#[cfg(all(
+    any(feature = "gen-llvm", feature = "gen-wasm"),
+    not(debug_assertions) // https://github.com/roc-lang/roc/issues/3898
+))]
+fn decode_tuple_two_elements() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            app "test" imports [Json] provides [main] to "./platform"
+
+            main =
+                when Str.toUtf8 "[\"ab\",10]" |> Decode.fromBytes Json.fromUtf8 is
+                    Ok ("ab", 10u8) -> "abcd"
+                    _ -> "something went wrong"
+            "#
+        ),
+        RocStr::from("abcd"),
+        RocStr
+    )
+}
+
+#[test]
+#[cfg(all(
+    any(feature = "gen-llvm", feature = "gen-wasm"),
+    not(debug_assertions) // https://github.com/roc-lang/roc/issues/3898
+))]
+fn decode_tuple_of_tuples() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            app "test" imports [Json] provides [main] to "./platform"
+
+            main =
+                when Str.toUtf8 "[[\"ab\",10],[\"cd\",25]]" |> Decode.fromBytes Json.fromUtf8 is
+                    Ok ( ("ab", 10u8), ("cd", 25u8) ) -> "abcd"
+                    _ -> "something went wrong"
+            "#
+        ),
+        RocStr::from("abcd"),
+        RocStr
+    )
+}
+
 #[cfg(all(test, any(feature = "gen-llvm", feature = "gen-wasm")))]
 mod hash {
     #[cfg(feature = "gen-llvm")]
@@ -1572,6 +1662,35 @@ mod hash {
             )
         }
 
+        #[test]
+        fn tuple_of_u8_and_str() {
+            assert_evals_to!(
+                &build_test(r#"(15u8, "bc")"#),
+                RocList::from_slice(&[15, 98, 99]),
+                RocList<u8>
+            )
+        }
+
+        #[test]
+        fn tuple_of_tuples() {
+            assert_evals_to!(
+                &build_test(r#"( (15u8, "bc"), (23u8, "ef") )"#),
+                RocList::from_slice(&[15, 98, 99, 23, 101, 102]),
+                RocList<u8>
+            )
+        }
+
+        #[test]
+        fn tuple_of_list_of_tuples() {
+            assert_evals_to!(
+                &build_test(
+                    r#"( [ ( 15u8, 32u8 ), ( 23u8, 41u8 ) ], [ (45u8, 63u8), (58u8, 73u8) ] )"#
+                ),
+                RocList::from_slice(&[15, 32, 23, 41, 45, 63, 58, 73]),
+                RocList<u8>
+            )
+        }
+
         #[test]
         fn hash_singleton_union() {
             assert_evals_to!(
@@ -1840,6 +1959,22 @@ mod eq {
     use indoc::indoc;
     use roc_std::RocStr;
 
+    #[test]
+    fn eq_tuple() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                app "test" provides [main] to "./platform"
+
+                main =
+                    ("a", "b") == ("a", "b")
+                "#
+            ),
+            true,
+            bool
+        )
+    }
+
     #[test]
     fn custom_eq_impl() {
         assert_evals_to!(

crates/compiler/test_mono/generated/encode_derived_nested_record_string.txt

@@ -1,5 +1,5 @@
 procedure #Derived.0 (#Derived.1):
-    let #Derived_gen.0 : Str = CallByName Encode.22 #Derived.1;
+    let #Derived_gen.0 : Str = CallByName Encode.23 #Derived.1;
     ret #Derived_gen.0;
 
 procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
@@ -8,11 +8,11 @@ procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
     let #Derived_gen.6 : {Str, Str} = Struct {#Derived_gen.7, #Derived_gen.8};
     let #Derived_gen.5 : List {Str, Str} = Array [#Derived_gen.6];
     let #Derived_gen.4 : List {Str, Str} = CallByName Json.20 #Derived_gen.5;
-    let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.3 #Derived_gen.4 #Derived.4;
+    let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.3 #Derived_gen.4 #Derived.4;
     ret #Derived_gen.3;
 
 procedure #Derived.5 (#Derived.6):
-    let #Derived_gen.14 : Str = CallByName Encode.22 #Derived.6;
+    let #Derived_gen.14 : Str = CallByName Encode.23 #Derived.6;
     ret #Derived_gen.14;
 
 procedure #Derived.7 (#Derived.8, #Derived.9, #Derived.6):
@@ -21,195 +21,195 @@ procedure #Derived.7 (#Derived.8, #Derived.9, #Derived.6):
     let #Derived_gen.20 : {Str, Str} = Struct {#Derived_gen.21, #Derived_gen.22};
     let #Derived_gen.19 : List {Str, Str} = Array [#Derived_gen.20];
     let #Derived_gen.18 : List {Str, Str} = CallByName Json.20 #Derived_gen.19;
-    let #Derived_gen.17 : List U8 = CallByName Encode.23 #Derived.8 #Derived_gen.18 #Derived.9;
+    let #Derived_gen.17 : List U8 = CallByName Encode.24 #Derived.8 #Derived_gen.18 #Derived.9;
     ret #Derived_gen.17;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName #Derived.2 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName #Derived.2 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.114 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.118 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.115 : List U8 = CallByName #Derived.7 Encode.94 Encode.96 Encode.102;
-    ret Encode.115;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.120 : List U8 = CallByName #Derived.7 Encode.99 Encode.101 Encode.107;
+    ret Encode.120;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.125 : List U8 = CallByName Json.114 Encode.94 Encode.96 Encode.102;
-    ret Encode.125;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.130 : List U8 = CallByName Json.118 Encode.99 Encode.101 Encode.107;
+    ret Encode.130;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.128 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.128;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.133 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.133;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : Str = CallByName #Derived.0 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : Str = CallByName #Derived.0 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.114 (Json.115, Json.428, Json.113):
-    let Json.461 : I64 = 123i64;
-    let Json.460 : U8 = CallByName Num.127 Json.461;
-    let Json.117 : List U8 = CallByName List.4 Json.115 Json.460;
-    let Json.459 : U64 = CallByName List.6 Json.113;
-    let Json.436 : {List U8, U64} = Struct {Json.117, Json.459};
-    let Json.437 : {} = Struct {};
-    let Json.435 : {List U8, U64} = CallByName List.18 Json.113 Json.436 Json.437;
-    dec Json.113;
-    let Json.119 : List U8 = StructAtIndex 0 Json.435;
-    inc Json.119;
-    dec Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.432 : List U8 = CallByName List.4 Json.119 Json.433;
-    ret Json.432;
+procedure Json.102 (Json.103, Json.562, Json.101):
+    let Json.571 : I64 = 34i64;
+    let Json.570 : U8 = CallByName Num.127 Json.571;
+    let Json.568 : List U8 = CallByName List.4 Json.103 Json.570;
+    let Json.569 : List U8 = CallByName Str.12 Json.101;
+    let Json.565 : List U8 = CallByName List.8 Json.568 Json.569;
+    let Json.567 : I64 = 34i64;
+    let Json.566 : U8 = CallByName Num.127 Json.567;
+    let Json.564 : List U8 = CallByName List.4 Json.565 Json.566;
+    ret Json.564;
 
-procedure Json.114 (Json.115, Json.428, Json.113):
-    let Json.501 : I64 = 123i64;
-    let Json.500 : U8 = CallByName Num.127 Json.501;
-    let Json.117 : List U8 = CallByName List.4 Json.115 Json.500;
-    let Json.499 : U64 = CallByName List.6 Json.113;
-    let Json.476 : {List U8, U64} = Struct {Json.117, Json.499};
-    let Json.477 : {} = Struct {};
-    let Json.475 : {List U8, U64} = CallByName List.18 Json.113 Json.476 Json.477;
-    dec Json.113;
-    let Json.119 : List U8 = StructAtIndex 0 Json.475;
-    inc Json.119;
-    dec Json.475;
-    let Json.474 : I64 = 125i64;
-    let Json.473 : U8 = CallByName Num.127 Json.474;
-    let Json.472 : List U8 = CallByName List.4 Json.119 Json.473;
-    ret Json.472;
-
-procedure Json.116 (Json.430, Json.431):
-    let Json.122 : Str = StructAtIndex 0 Json.431;
-    inc Json.122;
-    let Json.123 : Str = StructAtIndex 1 Json.431;
+procedure Json.118 (Json.119, Json.486, Json.117):
+    let Json.519 : I64 = 123i64;
+    let Json.518 : U8 = CallByName Num.127 Json.519;
+    let Json.121 : List U8 = CallByName List.4 Json.119 Json.518;
+    let Json.517 : U64 = CallByName List.6 Json.117;
+    let Json.494 : {List U8, U64} = Struct {Json.121, Json.517};
+    let Json.495 : {} = Struct {};
+    let Json.493 : {List U8, U64} = CallByName List.18 Json.117 Json.494 Json.495;
+    dec Json.117;
+    let Json.123 : List U8 = StructAtIndex 0 Json.493;
     inc Json.123;
-    dec Json.431;
-    let Json.120 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.120;
-    let Json.121 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.458 : I64 = 34i64;
-    let Json.457 : U8 = CallByName Num.127 Json.458;
-    let Json.455 : List U8 = CallByName List.4 Json.120 Json.457;
-    let Json.456 : List U8 = CallByName Str.12 Json.122;
-    let Json.452 : List U8 = CallByName List.8 Json.455 Json.456;
-    let Json.454 : I64 = 34i64;
-    let Json.453 : U8 = CallByName Num.127 Json.454;
-    let Json.449 : List U8 = CallByName List.4 Json.452 Json.453;
-    let Json.451 : I64 = 58i64;
-    let Json.450 : U8 = CallByName Num.127 Json.451;
-    let Json.447 : List U8 = CallByName List.4 Json.449 Json.450;
-    let Json.448 : {} = Struct {};
-    let Json.124 : List U8 = CallByName Encode.23 Json.447 Json.123 Json.448;
-    joinpoint Json.442 Json.125:
-        let Json.440 : U64 = 1i64;
-        let Json.439 : U64 = CallByName Num.20 Json.121 Json.440;
-        let Json.438 : {List U8, U64} = Struct {Json.125, Json.439};
-        ret Json.438;
-    in
-    let Json.446 : U64 = 1i64;
-    let Json.443 : Int1 = CallByName Num.24 Json.121 Json.446;
-    if Json.443 then
-        let Json.445 : I64 = 44i64;
-        let Json.444 : U8 = CallByName Num.127 Json.445;
-        let Json.441 : List U8 = CallByName List.4 Json.124 Json.444;
-        jump Json.442 Json.441;
-    else
-        jump Json.442 Json.124;
+    dec Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.490 : List U8 = CallByName List.4 Json.123 Json.491;
+    ret Json.490;
 
-procedure Json.116 (Json.430, Json.431):
-    let Json.122 : Str = StructAtIndex 0 Json.431;
-    inc Json.122;
-    let Json.123 : Str = StructAtIndex 1 Json.431;
+procedure Json.118 (Json.119, Json.486, Json.117):
+    let Json.559 : I64 = 123i64;
+    let Json.558 : U8 = CallByName Num.127 Json.559;
+    let Json.121 : List U8 = CallByName List.4 Json.119 Json.558;
+    let Json.557 : U64 = CallByName List.6 Json.117;
+    let Json.534 : {List U8, U64} = Struct {Json.121, Json.557};
+    let Json.535 : {} = Struct {};
+    let Json.533 : {List U8, U64} = CallByName List.18 Json.117 Json.534 Json.535;
+    dec Json.117;
+    let Json.123 : List U8 = StructAtIndex 0 Json.533;
     inc Json.123;
-    dec Json.431;
-    let Json.120 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.120;
-    let Json.121 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.498 : I64 = 34i64;
-    let Json.497 : U8 = CallByName Num.127 Json.498;
-    let Json.495 : List U8 = CallByName List.4 Json.120 Json.497;
-    let Json.496 : List U8 = CallByName Str.12 Json.122;
-    let Json.492 : List U8 = CallByName List.8 Json.495 Json.496;
-    let Json.494 : I64 = 34i64;
-    let Json.493 : U8 = CallByName Num.127 Json.494;
-    let Json.489 : List U8 = CallByName List.4 Json.492 Json.493;
-    let Json.491 : I64 = 58i64;
-    let Json.490 : U8 = CallByName Num.127 Json.491;
-    let Json.487 : List U8 = CallByName List.4 Json.489 Json.490;
-    let Json.488 : {} = Struct {};
-    let Json.124 : List U8 = CallByName Encode.23 Json.487 Json.123 Json.488;
-    joinpoint Json.482 Json.125:
-        let Json.480 : U64 = 1i64;
-        let Json.479 : U64 = CallByName Num.20 Json.121 Json.480;
-        let Json.478 : {List U8, U64} = Struct {Json.125, Json.479};
-        ret Json.478;
-    in
-    let Json.486 : U64 = 1i64;
-    let Json.483 : Int1 = CallByName Num.24 Json.121 Json.486;
-    if Json.483 then
-        let Json.485 : I64 = 44i64;
-        let Json.484 : U8 = CallByName Num.127 Json.485;
-        let Json.481 : List U8 = CallByName List.4 Json.124 Json.484;
-        jump Json.482 Json.481;
-    else
-        jump Json.482 Json.124;
+    dec Json.533;
+    let Json.532 : I64 = 125i64;
+    let Json.531 : U8 = CallByName Num.127 Json.532;
+    let Json.530 : List U8 = CallByName List.4 Json.123 Json.531;
+    ret Json.530;
 
-procedure Json.18 (Json.97):
-    let Json.502 : Str = CallByName Encode.22 Json.97;
-    ret Json.502;
-
-procedure Json.20 (Json.113):
-    let Json.426 : List {Str, Str} = CallByName Encode.22 Json.113;
-    ret Json.426;
-
-procedure Json.20 (Json.113):
-    let Json.468 : List {Str, Str} = CallByName Encode.22 Json.113;
-    ret Json.468;
-
-procedure Json.98 (Json.99, Json.504, Json.97):
-    let Json.513 : I64 = 34i64;
-    let Json.512 : U8 = CallByName Num.127 Json.513;
-    let Json.510 : List U8 = CallByName List.4 Json.99 Json.512;
-    let Json.511 : List U8 = CallByName Str.12 Json.97;
-    let Json.507 : List U8 = CallByName List.8 Json.510 Json.511;
-    let Json.509 : I64 = 34i64;
+procedure Json.120 (Json.488, Json.489):
+    let Json.126 : Str = StructAtIndex 0 Json.489;
+    inc Json.126;
+    let Json.127 : Str = StructAtIndex 1 Json.489;
+    inc Json.127;
+    dec Json.489;
+    let Json.124 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.124;
+    let Json.125 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.516 : I64 = 34i64;
+    let Json.515 : U8 = CallByName Num.127 Json.516;
+    let Json.513 : List U8 = CallByName List.4 Json.124 Json.515;
+    let Json.514 : List U8 = CallByName Str.12 Json.126;
+    let Json.510 : List U8 = CallByName List.8 Json.513 Json.514;
+    let Json.512 : I64 = 34i64;
+    let Json.511 : U8 = CallByName Num.127 Json.512;
+    let Json.507 : List U8 = CallByName List.4 Json.510 Json.511;
+    let Json.509 : I64 = 58i64;
     let Json.508 : U8 = CallByName Num.127 Json.509;
-    let Json.506 : List U8 = CallByName List.4 Json.507 Json.508;
-    ret Json.506;
+    let Json.505 : List U8 = CallByName List.4 Json.507 Json.508;
+    let Json.506 : {} = Struct {};
+    let Json.128 : List U8 = CallByName Encode.24 Json.505 Json.127 Json.506;
+    joinpoint Json.500 Json.129:
+        let Json.498 : U64 = 1i64;
+        let Json.497 : U64 = CallByName Num.20 Json.125 Json.498;
+        let Json.496 : {List U8, U64} = Struct {Json.129, Json.497};
+        ret Json.496;
+    in
+    let Json.504 : U64 = 1i64;
+    let Json.501 : Int1 = CallByName Num.24 Json.125 Json.504;
+    if Json.501 then
+        let Json.503 : I64 = 44i64;
+        let Json.502 : U8 = CallByName Num.127 Json.503;
+        let Json.499 : List U8 = CallByName List.4 Json.128 Json.502;
+        jump Json.500 Json.499;
+    else
+        jump Json.500 Json.128;
+
+procedure Json.120 (Json.488, Json.489):
+    let Json.126 : Str = StructAtIndex 0 Json.489;
+    inc Json.126;
+    let Json.127 : Str = StructAtIndex 1 Json.489;
+    inc Json.127;
+    dec Json.489;
+    let Json.124 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.124;
+    let Json.125 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.556 : I64 = 34i64;
+    let Json.555 : U8 = CallByName Num.127 Json.556;
+    let Json.553 : List U8 = CallByName List.4 Json.124 Json.555;
+    let Json.554 : List U8 = CallByName Str.12 Json.126;
+    let Json.550 : List U8 = CallByName List.8 Json.553 Json.554;
+    let Json.552 : I64 = 34i64;
+    let Json.551 : U8 = CallByName Num.127 Json.552;
+    let Json.547 : List U8 = CallByName List.4 Json.550 Json.551;
+    let Json.549 : I64 = 58i64;
+    let Json.548 : U8 = CallByName Num.127 Json.549;
+    let Json.545 : List U8 = CallByName List.4 Json.547 Json.548;
+    let Json.546 : {} = Struct {};
+    let Json.128 : List U8 = CallByName Encode.24 Json.545 Json.127 Json.546;
+    joinpoint Json.540 Json.129:
+        let Json.538 : U64 = 1i64;
+        let Json.537 : U64 = CallByName Num.20 Json.125 Json.538;
+        let Json.536 : {List U8, U64} = Struct {Json.129, Json.537};
+        ret Json.536;
+    in
+    let Json.544 : U64 = 1i64;
+    let Json.541 : Int1 = CallByName Num.24 Json.125 Json.544;
+    if Json.541 then
+        let Json.543 : I64 = 44i64;
+        let Json.542 : U8 = CallByName Num.127 Json.543;
+        let Json.539 : List U8 = CallByName List.4 Json.128 Json.542;
+        jump Json.540 Json.539;
+    else
+        jump Json.540 Json.128;
+
+procedure Json.18 (Json.101):
+    let Json.560 : Str = CallByName Encode.23 Json.101;
+    ret Json.560;
+
+procedure Json.20 (Json.117):
+    let Json.484 : List {Str, Str} = CallByName Encode.23 Json.117;
+    ret Json.484;
+
+procedure Json.20 (Json.117):
+    let Json.526 : List {Str, Str} = CallByName Encode.23 Json.117;
+    ret Json.526;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.535 : {List U8, U64} = CallByName Json.116 List.140 List.141;
+    let List.535 : {List U8, U64} = CallByName Json.120 List.140 List.141;
     ret List.535;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.608 : {List U8, U64} = CallByName Json.116 List.140 List.141;
+    let List.608 : {List U8, U64} = CallByName Json.120 List.140 List.141;
     ret List.608;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -348,7 +348,7 @@ procedure Str.9 (Str.77):
 procedure Test.0 ():
     let Test.12 : Str = "bar";
     let Test.10 : {} = CallByName Json.1;
-    let Test.8 : List U8 = CallByName Encode.25 Test.12 Test.10;
+    let Test.8 : List U8 = CallByName Encode.26 Test.12 Test.10;
     let Test.1 : [C {U64, U8}, C Str] = CallByName Str.9 Test.8;
     let Test.5 : U8 = 1i64;
     let Test.6 : U8 = GetTagId Test.1;

crates/compiler/test_mono/generated/encode_derived_record_one_field_string.txt

@@ -1,5 +1,5 @@
 procedure #Derived.0 (#Derived.1):
-    let #Derived_gen.0 : Str = CallByName Encode.22 #Derived.1;
+    let #Derived_gen.0 : Str = CallByName Encode.23 #Derived.1;
     ret #Derived_gen.0;
 
 procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
@@ -8,117 +8,117 @@ procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
     let #Derived_gen.6 : {Str, Str} = Struct {#Derived_gen.7, #Derived_gen.8};
     let #Derived_gen.5 : List {Str, Str} = Array [#Derived_gen.6];
     let #Derived_gen.4 : List {Str, Str} = CallByName Json.20 #Derived_gen.5;
-    let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.3 #Derived_gen.4 #Derived.4;
+    let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.3 #Derived_gen.4 #Derived.4;
     ret #Derived_gen.3;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName #Derived.2 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName #Derived.2 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.114 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.118 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.116 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.116;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.121 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.121;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : Str = CallByName #Derived.0 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : Str = CallByName #Derived.0 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.114 (Json.115, Json.428, Json.113):
-    let Json.461 : I64 = 123i64;
-    let Json.460 : U8 = CallByName Num.127 Json.461;
-    let Json.117 : List U8 = CallByName List.4 Json.115 Json.460;
-    let Json.459 : U64 = CallByName List.6 Json.113;
-    let Json.436 : {List U8, U64} = Struct {Json.117, Json.459};
-    let Json.437 : {} = Struct {};
-    let Json.435 : {List U8, U64} = CallByName List.18 Json.113 Json.436 Json.437;
-    dec Json.113;
-    let Json.119 : List U8 = StructAtIndex 0 Json.435;
-    inc Json.119;
-    dec Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.432 : List U8 = CallByName List.4 Json.119 Json.433;
-    ret Json.432;
+procedure Json.102 (Json.103, Json.522, Json.101):
+    let Json.531 : I64 = 34i64;
+    let Json.530 : U8 = CallByName Num.127 Json.531;
+    let Json.528 : List U8 = CallByName List.4 Json.103 Json.530;
+    let Json.529 : List U8 = CallByName Str.12 Json.101;
+    let Json.525 : List U8 = CallByName List.8 Json.528 Json.529;
+    let Json.527 : I64 = 34i64;
+    let Json.526 : U8 = CallByName Num.127 Json.527;
+    let Json.524 : List U8 = CallByName List.4 Json.525 Json.526;
+    ret Json.524;
 
-procedure Json.116 (Json.430, Json.431):
-    let Json.122 : Str = StructAtIndex 0 Json.431;
-    inc Json.122;
-    let Json.123 : Str = StructAtIndex 1 Json.431;
+procedure Json.118 (Json.119, Json.486, Json.117):
+    let Json.519 : I64 = 123i64;
+    let Json.518 : U8 = CallByName Num.127 Json.519;
+    let Json.121 : List U8 = CallByName List.4 Json.119 Json.518;
+    let Json.517 : U64 = CallByName List.6 Json.117;
+    let Json.494 : {List U8, U64} = Struct {Json.121, Json.517};
+    let Json.495 : {} = Struct {};
+    let Json.493 : {List U8, U64} = CallByName List.18 Json.117 Json.494 Json.495;
+    dec Json.117;
+    let Json.123 : List U8 = StructAtIndex 0 Json.493;
     inc Json.123;
-    dec Json.431;
-    let Json.120 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.120;
-    let Json.121 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.458 : I64 = 34i64;
-    let Json.457 : U8 = CallByName Num.127 Json.458;
-    let Json.455 : List U8 = CallByName List.4 Json.120 Json.457;
-    let Json.456 : List U8 = CallByName Str.12 Json.122;
-    let Json.452 : List U8 = CallByName List.8 Json.455 Json.456;
-    let Json.454 : I64 = 34i64;
-    let Json.453 : U8 = CallByName Num.127 Json.454;
-    let Json.449 : List U8 = CallByName List.4 Json.452 Json.453;
-    let Json.451 : I64 = 58i64;
-    let Json.450 : U8 = CallByName Num.127 Json.451;
-    let Json.447 : List U8 = CallByName List.4 Json.449 Json.450;
-    let Json.448 : {} = Struct {};
-    let Json.124 : List U8 = CallByName Encode.23 Json.447 Json.123 Json.448;
-    joinpoint Json.442 Json.125:
-        let Json.440 : U64 = 1i64;
-        let Json.439 : U64 = CallByName Num.20 Json.121 Json.440;
-        let Json.438 : {List U8, U64} = Struct {Json.125, Json.439};
-        ret Json.438;
+    dec Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.490 : List U8 = CallByName List.4 Json.123 Json.491;
+    ret Json.490;
+
+procedure Json.120 (Json.488, Json.489):
+    let Json.126 : Str = StructAtIndex 0 Json.489;
+    inc Json.126;
+    let Json.127 : Str = StructAtIndex 1 Json.489;
+    inc Json.127;
+    dec Json.489;
+    let Json.124 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.124;
+    let Json.125 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.516 : I64 = 34i64;
+    let Json.515 : U8 = CallByName Num.127 Json.516;
+    let Json.513 : List U8 = CallByName List.4 Json.124 Json.515;
+    let Json.514 : List U8 = CallByName Str.12 Json.126;
+    let Json.510 : List U8 = CallByName List.8 Json.513 Json.514;
+    let Json.512 : I64 = 34i64;
+    let Json.511 : U8 = CallByName Num.127 Json.512;
+    let Json.507 : List U8 = CallByName List.4 Json.510 Json.511;
+    let Json.509 : I64 = 58i64;
+    let Json.508 : U8 = CallByName Num.127 Json.509;
+    let Json.505 : List U8 = CallByName List.4 Json.507 Json.508;
+    let Json.506 : {} = Struct {};
+    let Json.128 : List U8 = CallByName Encode.24 Json.505 Json.127 Json.506;
+    joinpoint Json.500 Json.129:
+        let Json.498 : U64 = 1i64;
+        let Json.497 : U64 = CallByName Num.20 Json.125 Json.498;
+        let Json.496 : {List U8, U64} = Struct {Json.129, Json.497};
+        ret Json.496;
     in
-    let Json.446 : U64 = 1i64;
-    let Json.443 : Int1 = CallByName Num.24 Json.121 Json.446;
-    if Json.443 then
-        let Json.445 : I64 = 44i64;
-        let Json.444 : U8 = CallByName Num.127 Json.445;
-        let Json.441 : List U8 = CallByName List.4 Json.124 Json.444;
-        jump Json.442 Json.441;
+    let Json.504 : U64 = 1i64;
+    let Json.501 : Int1 = CallByName Num.24 Json.125 Json.504;
+    if Json.501 then
+        let Json.503 : I64 = 44i64;
+        let Json.502 : U8 = CallByName Num.127 Json.503;
+        let Json.499 : List U8 = CallByName List.4 Json.128 Json.502;
+        jump Json.500 Json.499;
     else
-        jump Json.442 Json.124;
+        jump Json.500 Json.128;
 
-procedure Json.18 (Json.97):
-    let Json.462 : Str = CallByName Encode.22 Json.97;
-    ret Json.462;
+procedure Json.18 (Json.101):
+    let Json.520 : Str = CallByName Encode.23 Json.101;
+    ret Json.520;
 
-procedure Json.20 (Json.113):
-    let Json.426 : List {Str, Str} = CallByName Encode.22 Json.113;
-    ret Json.426;
-
-procedure Json.98 (Json.99, Json.464, Json.97):
-    let Json.473 : I64 = 34i64;
-    let Json.472 : U8 = CallByName Num.127 Json.473;
-    let Json.470 : List U8 = CallByName List.4 Json.99 Json.472;
-    let Json.471 : List U8 = CallByName Str.12 Json.97;
-    let Json.467 : List U8 = CallByName List.8 Json.470 Json.471;
-    let Json.469 : I64 = 34i64;
-    let Json.468 : U8 = CallByName Num.127 Json.469;
-    let Json.466 : List U8 = CallByName List.4 Json.467 Json.468;
-    ret Json.466;
+procedure Json.20 (Json.117):
+    let Json.484 : List {Str, Str} = CallByName Encode.23 Json.117;
+    ret Json.484;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.541 : {List U8, U64} = CallByName Json.116 List.140 List.141;
+    let List.541 : {List U8, U64} = CallByName Json.120 List.140 List.141;
     ret List.541;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -225,7 +225,7 @@ procedure Str.9 (Str.77):
 procedure Test.0 ():
     let Test.11 : Str = "foo";
     let Test.10 : {} = CallByName Json.1;
-    let Test.8 : List U8 = CallByName Encode.25 Test.11 Test.10;
+    let Test.8 : List U8 = CallByName Encode.26 Test.11 Test.10;
     let Test.1 : [C {U64, U8}, C Str] = CallByName Str.9 Test.8;
     let Test.5 : U8 = 1i64;
     let Test.6 : U8 = GetTagId Test.1;

crates/compiler/test_mono/generated/encode_derived_record_two_field_strings.txt

@@ -1,5 +1,5 @@
 procedure #Derived.0 (#Derived.1):
-    let #Derived_gen.0 : {Str, Str} = CallByName Encode.22 #Derived.1;
+    let #Derived_gen.0 : {Str, Str} = CallByName Encode.23 #Derived.1;
     ret #Derived_gen.0;
 
 procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
@@ -16,117 +16,117 @@ procedure #Derived.2 (#Derived.3, #Derived.4, #Derived.1):
     let #Derived_gen.7 : {Str, Str} = Struct {#Derived_gen.8, #Derived_gen.9};
     let #Derived_gen.5 : List {Str, Str} = Array [#Derived_gen.6, #Derived_gen.7];
     let #Derived_gen.4 : List {Str, Str} = CallByName Json.20 #Derived_gen.5;
-    let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.3 #Derived_gen.4 #Derived.4;
+    let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.3 #Derived_gen.4 #Derived.4;
     ret #Derived_gen.3;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName #Derived.2 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName #Derived.2 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.114 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.118 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.117 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.117;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.122 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.122;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : {Str, Str} = CallByName #Derived.0 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : {Str, Str} = CallByName #Derived.0 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.114 (Json.115, Json.428, Json.113):
-    let Json.461 : I64 = 123i64;
-    let Json.460 : U8 = CallByName Num.127 Json.461;
-    let Json.117 : List U8 = CallByName List.4 Json.115 Json.460;
-    let Json.459 : U64 = CallByName List.6 Json.113;
-    let Json.436 : {List U8, U64} = Struct {Json.117, Json.459};
-    let Json.437 : {} = Struct {};
-    let Json.435 : {List U8, U64} = CallByName List.18 Json.113 Json.436 Json.437;
-    dec Json.113;
-    let Json.119 : List U8 = StructAtIndex 0 Json.435;
-    inc Json.119;
-    dec Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.432 : List U8 = CallByName List.4 Json.119 Json.433;
-    ret Json.432;
+procedure Json.102 (Json.103, Json.522, Json.101):
+    let Json.531 : I64 = 34i64;
+    let Json.530 : U8 = CallByName Num.127 Json.531;
+    let Json.528 : List U8 = CallByName List.4 Json.103 Json.530;
+    let Json.529 : List U8 = CallByName Str.12 Json.101;
+    let Json.525 : List U8 = CallByName List.8 Json.528 Json.529;
+    let Json.527 : I64 = 34i64;
+    let Json.526 : U8 = CallByName Num.127 Json.527;
+    let Json.524 : List U8 = CallByName List.4 Json.525 Json.526;
+    ret Json.524;
 
-procedure Json.116 (Json.430, Json.431):
-    let Json.122 : Str = StructAtIndex 0 Json.431;
-    inc Json.122;
-    let Json.123 : Str = StructAtIndex 1 Json.431;
+procedure Json.118 (Json.119, Json.486, Json.117):
+    let Json.519 : I64 = 123i64;
+    let Json.518 : U8 = CallByName Num.127 Json.519;
+    let Json.121 : List U8 = CallByName List.4 Json.119 Json.518;
+    let Json.517 : U64 = CallByName List.6 Json.117;
+    let Json.494 : {List U8, U64} = Struct {Json.121, Json.517};
+    let Json.495 : {} = Struct {};
+    let Json.493 : {List U8, U64} = CallByName List.18 Json.117 Json.494 Json.495;
+    dec Json.117;
+    let Json.123 : List U8 = StructAtIndex 0 Json.493;
     inc Json.123;
-    dec Json.431;
-    let Json.120 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.120;
-    let Json.121 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.458 : I64 = 34i64;
-    let Json.457 : U8 = CallByName Num.127 Json.458;
-    let Json.455 : List U8 = CallByName List.4 Json.120 Json.457;
-    let Json.456 : List U8 = CallByName Str.12 Json.122;
-    let Json.452 : List U8 = CallByName List.8 Json.455 Json.456;
-    let Json.454 : I64 = 34i64;
-    let Json.453 : U8 = CallByName Num.127 Json.454;
-    let Json.449 : List U8 = CallByName List.4 Json.452 Json.453;
-    let Json.451 : I64 = 58i64;
-    let Json.450 : U8 = CallByName Num.127 Json.451;
-    let Json.447 : List U8 = CallByName List.4 Json.449 Json.450;
-    let Json.448 : {} = Struct {};
-    let Json.124 : List U8 = CallByName Encode.23 Json.447 Json.123 Json.448;
-    joinpoint Json.442 Json.125:
-        let Json.440 : U64 = 1i64;
-        let Json.439 : U64 = CallByName Num.20 Json.121 Json.440;
-        let Json.438 : {List U8, U64} = Struct {Json.125, Json.439};
-        ret Json.438;
+    dec Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.490 : List U8 = CallByName List.4 Json.123 Json.491;
+    ret Json.490;
+
+procedure Json.120 (Json.488, Json.489):
+    let Json.126 : Str = StructAtIndex 0 Json.489;
+    inc Json.126;
+    let Json.127 : Str = StructAtIndex 1 Json.489;
+    inc Json.127;
+    dec Json.489;
+    let Json.124 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.124;
+    let Json.125 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.516 : I64 = 34i64;
+    let Json.515 : U8 = CallByName Num.127 Json.516;
+    let Json.513 : List U8 = CallByName List.4 Json.124 Json.515;
+    let Json.514 : List U8 = CallByName Str.12 Json.126;
+    let Json.510 : List U8 = CallByName List.8 Json.513 Json.514;
+    let Json.512 : I64 = 34i64;
+    let Json.511 : U8 = CallByName Num.127 Json.512;
+    let Json.507 : List U8 = CallByName List.4 Json.510 Json.511;
+    let Json.509 : I64 = 58i64;
+    let Json.508 : U8 = CallByName Num.127 Json.509;
+    let Json.505 : List U8 = CallByName List.4 Json.507 Json.508;
+    let Json.506 : {} = Struct {};
+    let Json.128 : List U8 = CallByName Encode.24 Json.505 Json.127 Json.506;
+    joinpoint Json.500 Json.129:
+        let Json.498 : U64 = 1i64;
+        let Json.497 : U64 = CallByName Num.20 Json.125 Json.498;
+        let Json.496 : {List U8, U64} = Struct {Json.129, Json.497};
+        ret Json.496;
     in
-    let Json.446 : U64 = 1i64;
-    let Json.443 : Int1 = CallByName Num.24 Json.121 Json.446;
-    if Json.443 then
-        let Json.445 : I64 = 44i64;
-        let Json.444 : U8 = CallByName Num.127 Json.445;
-        let Json.441 : List U8 = CallByName List.4 Json.124 Json.444;
-        jump Json.442 Json.441;
+    let Json.504 : U64 = 1i64;
+    let Json.501 : Int1 = CallByName Num.24 Json.125 Json.504;
+    if Json.501 then
+        let Json.503 : I64 = 44i64;
+        let Json.502 : U8 = CallByName Num.127 Json.503;
+        let Json.499 : List U8 = CallByName List.4 Json.128 Json.502;
+        jump Json.500 Json.499;
     else
-        jump Json.442 Json.124;
+        jump Json.500 Json.128;
 
-procedure Json.18 (Json.97):
-    let Json.474 : Str = CallByName Encode.22 Json.97;
-    ret Json.474;
+procedure Json.18 (Json.101):
+    let Json.532 : Str = CallByName Encode.23 Json.101;
+    ret Json.532;
 
-procedure Json.20 (Json.113):
-    let Json.426 : List {Str, Str} = CallByName Encode.22 Json.113;
-    ret Json.426;
-
-procedure Json.98 (Json.99, Json.464, Json.97):
-    let Json.473 : I64 = 34i64;
-    let Json.472 : U8 = CallByName Num.127 Json.473;
-    let Json.470 : List U8 = CallByName List.4 Json.99 Json.472;
-    let Json.471 : List U8 = CallByName Str.12 Json.97;
-    let Json.467 : List U8 = CallByName List.8 Json.470 Json.471;
-    let Json.469 : I64 = 34i64;
-    let Json.468 : U8 = CallByName Num.127 Json.469;
-    let Json.466 : List U8 = CallByName List.4 Json.467 Json.468;
-    ret Json.466;
+procedure Json.20 (Json.117):
+    let Json.484 : List {Str, Str} = CallByName Encode.23 Json.117;
+    ret Json.484;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.541 : {List U8, U64} = CallByName Json.116 List.140 List.141;
+    let List.541 : {List U8, U64} = CallByName Json.120 List.140 List.141;
     ret List.541;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -235,7 +235,7 @@ procedure Test.0 ():
     let Test.12 : Str = "bar";
     let Test.9 : {Str, Str} = Struct {Test.11, Test.12};
     let Test.10 : {} = CallByName Json.1;
-    let Test.8 : List U8 = CallByName Encode.25 Test.9 Test.10;
+    let Test.8 : List U8 = CallByName Encode.26 Test.9 Test.10;
     let Test.1 : [C {U64, U8}, C Str] = CallByName Str.9 Test.8;
     let Test.5 : U8 = 1i64;
     let Test.6 : U8 = GetTagId Test.1;

crates/compiler/test_mono/generated/encode_derived_string.txt

@@ -1,34 +1,34 @@
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : Str = CallByName Json.18 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : Str = CallByName Json.18 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.18 (Json.97):
-    let Json.426 : Str = CallByName Encode.22 Json.97;
-    ret Json.426;
+procedure Json.102 (Json.103, Json.486, Json.101):
+    let Json.495 : I64 = 34i64;
+    let Json.494 : U8 = CallByName Num.127 Json.495;
+    let Json.492 : List U8 = CallByName List.4 Json.103 Json.494;
+    let Json.493 : List U8 = CallByName Str.12 Json.101;
+    let Json.489 : List U8 = CallByName List.8 Json.492 Json.493;
+    let Json.491 : I64 = 34i64;
+    let Json.490 : U8 = CallByName Num.127 Json.491;
+    let Json.488 : List U8 = CallByName List.4 Json.489 Json.490;
+    ret Json.488;
 
-procedure Json.98 (Json.99, Json.428, Json.97):
-    let Json.437 : I64 = 34i64;
-    let Json.436 : U8 = CallByName Num.127 Json.437;
-    let Json.434 : List U8 = CallByName List.4 Json.99 Json.436;
-    let Json.435 : List U8 = CallByName Str.12 Json.97;
-    let Json.431 : List U8 = CallByName List.8 Json.434 Json.435;
-    let Json.433 : I64 = 34i64;
-    let Json.432 : U8 = CallByName Num.127 Json.433;
-    let Json.430 : List U8 = CallByName List.4 Json.431 Json.432;
-    ret Json.430;
+procedure Json.18 (Json.101):
+    let Json.484 : Str = CallByName Encode.23 Json.101;
+    ret Json.484;
 
 procedure List.4 (List.107, List.108):
     let List.503 : U64 = 1i64;
@@ -86,7 +86,7 @@ procedure Str.9 (Str.77):
 procedure Test.0 ():
     let Test.9 : Str = "abc";
     let Test.10 : {} = CallByName Json.1;
-    let Test.8 : List U8 = CallByName Encode.25 Test.9 Test.10;
+    let Test.8 : List U8 = CallByName Encode.26 Test.9 Test.10;
     let Test.1 : [C {U64, U8}, C Str] = CallByName Str.9 Test.8;
     let Test.5 : U8 = 1i64;
     let Test.6 : U8 = GetTagId Test.1;

crates/compiler/test_mono/generated/encode_derived_tag_one_field_string.txt

@@ -1,133 +1,133 @@
 procedure #Derived.0 (#Derived.1):
-    let #Derived_gen.0 : Str = CallByName Encode.22 #Derived.1;
+    let #Derived_gen.0 : Str = CallByName Encode.23 #Derived.1;
     ret #Derived_gen.0;
 
 procedure #Derived.3 (#Derived.4, #Derived.5, #Derived.1):
     joinpoint #Derived_gen.5 #Derived_gen.4:
-        let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.4 #Derived_gen.4 #Derived.5;
+        let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.4 #Derived_gen.4 #Derived.5;
         ret #Derived_gen.3;
     in
     let #Derived_gen.7 : Str = "A";
     let #Derived_gen.9 : Str = CallByName Json.18 #Derived.1;
     let #Derived_gen.8 : List Str = Array [#Derived_gen.9];
-    let #Derived_gen.6 : {Str, List Str} = CallByName Json.21 #Derived_gen.7 #Derived_gen.8;
+    let #Derived_gen.6 : {Str, List Str} = CallByName Json.22 #Derived_gen.7 #Derived_gen.8;
     jump #Derived_gen.5 #Derived_gen.6;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName #Derived.3 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName #Derived.3 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.128 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.144 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.116 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.116;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.121 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.121;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : Str = CallByName #Derived.0 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : Str = CallByName #Derived.0 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.128 (Json.129, Json.428, #Attr.12):
-    let Json.127 : List Str = StructAtIndex 1 #Attr.12;
-    inc Json.127;
-    let Json.126 : Str = StructAtIndex 0 #Attr.12;
-    inc Json.126;
+procedure Json.102 (Json.103, Json.527, Json.101):
+    let Json.536 : I64 = 34i64;
+    let Json.535 : U8 = CallByName Num.127 Json.536;
+    let Json.533 : List U8 = CallByName List.4 Json.103 Json.535;
+    let Json.534 : List U8 = CallByName Str.12 Json.101;
+    let Json.530 : List U8 = CallByName List.8 Json.533 Json.534;
+    let Json.532 : I64 = 34i64;
+    let Json.531 : U8 = CallByName Num.127 Json.532;
+    let Json.529 : List U8 = CallByName List.4 Json.530 Json.531;
+    ret Json.529;
+
+procedure Json.144 (Json.145, Json.486, #Attr.12):
+    let Json.143 : List Str = StructAtIndex 1 #Attr.12;
+    inc Json.143;
+    let Json.142 : Str = StructAtIndex 0 #Attr.12;
+    inc Json.142;
     dec #Attr.12;
-    let Json.466 : I64 = 123i64;
-    let Json.465 : U8 = CallByName Num.127 Json.466;
-    let Json.462 : List U8 = CallByName List.4 Json.129 Json.465;
-    let Json.464 : I64 = 34i64;
-    let Json.463 : U8 = CallByName Num.127 Json.464;
-    let Json.460 : List U8 = CallByName List.4 Json.462 Json.463;
-    let Json.461 : List U8 = CallByName Str.12 Json.126;
-    let Json.457 : List U8 = CallByName List.8 Json.460 Json.461;
-    let Json.459 : I64 = 34i64;
-    let Json.458 : U8 = CallByName Num.127 Json.459;
-    let Json.454 : List U8 = CallByName List.4 Json.457 Json.458;
-    let Json.456 : I64 = 58i64;
-    let Json.455 : U8 = CallByName Num.127 Json.456;
-    let Json.451 : List U8 = CallByName List.4 Json.454 Json.455;
-    let Json.453 : I64 = 91i64;
-    let Json.452 : U8 = CallByName Num.127 Json.453;
-    let Json.131 : List U8 = CallByName List.4 Json.451 Json.452;
-    let Json.450 : U64 = CallByName List.6 Json.127;
-    let Json.438 : {List U8, U64} = Struct {Json.131, Json.450};
-    let Json.439 : {} = Struct {};
-    let Json.437 : {List U8, U64} = CallByName List.18 Json.127 Json.438 Json.439;
-    dec Json.127;
-    let Json.133 : List U8 = StructAtIndex 0 Json.437;
-    inc Json.133;
-    dec Json.437;
-    let Json.436 : I64 = 93i64;
-    let Json.435 : U8 = CallByName Num.127 Json.436;
-    let Json.432 : List U8 = CallByName List.4 Json.133 Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.431 : List U8 = CallByName List.4 Json.432 Json.433;
-    ret Json.431;
+    let Json.524 : I64 = 123i64;
+    let Json.523 : U8 = CallByName Num.127 Json.524;
+    let Json.520 : List U8 = CallByName List.4 Json.145 Json.523;
+    let Json.522 : I64 = 34i64;
+    let Json.521 : U8 = CallByName Num.127 Json.522;
+    let Json.518 : List U8 = CallByName List.4 Json.520 Json.521;
+    let Json.519 : List U8 = CallByName Str.12 Json.142;
+    let Json.515 : List U8 = CallByName List.8 Json.518 Json.519;
+    let Json.517 : I64 = 34i64;
+    let Json.516 : U8 = CallByName Num.127 Json.517;
+    let Json.512 : List U8 = CallByName List.4 Json.515 Json.516;
+    let Json.514 : I64 = 58i64;
+    let Json.513 : U8 = CallByName Num.127 Json.514;
+    let Json.509 : List U8 = CallByName List.4 Json.512 Json.513;
+    let Json.511 : I64 = 91i64;
+    let Json.510 : U8 = CallByName Num.127 Json.511;
+    let Json.147 : List U8 = CallByName List.4 Json.509 Json.510;
+    let Json.508 : U64 = CallByName List.6 Json.143;
+    let Json.496 : {List U8, U64} = Struct {Json.147, Json.508};
+    let Json.497 : {} = Struct {};
+    let Json.495 : {List U8, U64} = CallByName List.18 Json.143 Json.496 Json.497;
+    dec Json.143;
+    let Json.149 : List U8 = StructAtIndex 0 Json.495;
+    inc Json.149;
+    dec Json.495;
+    let Json.494 : I64 = 93i64;
+    let Json.493 : U8 = CallByName Num.127 Json.494;
+    let Json.490 : List U8 = CallByName List.4 Json.149 Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.489 : List U8 = CallByName List.4 Json.490 Json.491;
+    ret Json.489;
 
-procedure Json.130 (Json.430, Json.136):
-    let Json.134 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.134;
-    let Json.135 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.449 : {} = Struct {};
-    let Json.137 : List U8 = CallByName Encode.23 Json.134 Json.136 Json.449;
-    joinpoint Json.444 Json.138:
-        let Json.442 : U64 = 1i64;
-        let Json.441 : U64 = CallByName Num.20 Json.135 Json.442;
-        let Json.440 : {List U8, U64} = Struct {Json.138, Json.441};
-        ret Json.440;
+procedure Json.146 (Json.488, Json.152):
+    let Json.150 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.150;
+    let Json.151 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.507 : {} = Struct {};
+    let Json.153 : List U8 = CallByName Encode.24 Json.150 Json.152 Json.507;
+    joinpoint Json.502 Json.154:
+        let Json.500 : U64 = 1i64;
+        let Json.499 : U64 = CallByName Num.20 Json.151 Json.500;
+        let Json.498 : {List U8, U64} = Struct {Json.154, Json.499};
+        ret Json.498;
     in
-    let Json.448 : U64 = 1i64;
-    let Json.445 : Int1 = CallByName Num.24 Json.135 Json.448;
-    if Json.445 then
-        let Json.447 : I64 = 44i64;
-        let Json.446 : U8 = CallByName Num.127 Json.447;
-        let Json.443 : List U8 = CallByName List.4 Json.137 Json.446;
-        jump Json.444 Json.443;
+    let Json.506 : U64 = 1i64;
+    let Json.503 : Int1 = CallByName Num.24 Json.151 Json.506;
+    if Json.503 then
+        let Json.505 : I64 = 44i64;
+        let Json.504 : U8 = CallByName Num.127 Json.505;
+        let Json.501 : List U8 = CallByName List.4 Json.153 Json.504;
+        jump Json.502 Json.501;
     else
-        jump Json.444 Json.137;
+        jump Json.502 Json.153;
 
-procedure Json.18 (Json.97):
-    let Json.467 : Str = CallByName Encode.22 Json.97;
-    ret Json.467;
+procedure Json.18 (Json.101):
+    let Json.525 : Str = CallByName Encode.23 Json.101;
+    ret Json.525;
 
-procedure Json.21 (Json.126, Json.127):
-    let Json.427 : {Str, List Str} = Struct {Json.126, Json.127};
-    let Json.426 : {Str, List Str} = CallByName Encode.22 Json.427;
-    ret Json.426;
-
-procedure Json.98 (Json.99, Json.469, Json.97):
-    let Json.478 : I64 = 34i64;
-    let Json.477 : U8 = CallByName Num.127 Json.478;
-    let Json.475 : List U8 = CallByName List.4 Json.99 Json.477;
-    let Json.476 : List U8 = CallByName Str.12 Json.97;
-    let Json.472 : List U8 = CallByName List.8 Json.475 Json.476;
-    let Json.474 : I64 = 34i64;
-    let Json.473 : U8 = CallByName Num.127 Json.474;
-    let Json.471 : List U8 = CallByName List.4 Json.472 Json.473;
-    ret Json.471;
+procedure Json.22 (Json.142, Json.143):
+    let Json.485 : {Str, List Str} = Struct {Json.142, Json.143};
+    let Json.484 : {Str, List Str} = CallByName Encode.23 Json.485;
+    ret Json.484;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.547 : {List U8, U64} = CallByName Json.130 List.140 List.141;
+    let List.547 : {List U8, U64} = CallByName Json.146 List.140 List.141;
     ret List.547;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -234,7 +234,7 @@ procedure Str.9 (Str.77):
 procedure Test.0 ():
     let Test.12 : Str = "foo";
     let Test.11 : {} = CallByName Json.1;
-    let Test.10 : List U8 = CallByName Encode.25 Test.12 Test.11;
+    let Test.10 : List U8 = CallByName Encode.26 Test.12 Test.11;
     let Test.2 : [C {U64, U8}, C Str] = CallByName Str.9 Test.10;
     let Test.7 : U8 = 1i64;
     let Test.8 : U8 = GetTagId Test.2;

crates/compiler/test_mono/generated/encode_derived_tag_two_payloads_string.txt

@@ -1,10 +1,10 @@
 procedure #Derived.0 (#Derived.1):
-    let #Derived_gen.0 : {Str, Str} = CallByName Encode.22 #Derived.1;
+    let #Derived_gen.0 : {Str, Str} = CallByName Encode.23 #Derived.1;
     ret #Derived_gen.0;
 
 procedure #Derived.4 (#Derived.5, #Derived.6, #Derived.1):
     joinpoint #Derived_gen.5 #Derived_gen.4:
-        let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.5 #Derived_gen.4 #Derived.6;
+        let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.5 #Derived_gen.4 #Derived.6;
         ret #Derived_gen.3;
     in
     let #Derived.2 : Str = StructAtIndex 0 #Derived.1;
@@ -16,124 +16,124 @@ procedure #Derived.4 (#Derived.5, #Derived.6, #Derived.1):
     let #Derived_gen.9 : Str = CallByName Json.18 #Derived.2;
     let #Derived_gen.10 : Str = CallByName Json.18 #Derived.3;
     let #Derived_gen.8 : List Str = Array [#Derived_gen.9, #Derived_gen.10];
-    let #Derived_gen.6 : {Str, List Str} = CallByName Json.21 #Derived_gen.7 #Derived_gen.8;
+    let #Derived_gen.6 : {Str, List Str} = CallByName Json.22 #Derived_gen.7 #Derived_gen.8;
     jump #Derived_gen.5 #Derived_gen.6;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName #Derived.4 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName #Derived.4 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.128 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.144 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.117 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
-    ret Encode.117;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.122 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.122;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : {Str, Str} = CallByName #Derived.0 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : {Str, Str} = CallByName #Derived.0 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.128 (Json.129, Json.428, #Attr.12):
-    let Json.127 : List Str = StructAtIndex 1 #Attr.12;
-    inc Json.127;
-    let Json.126 : Str = StructAtIndex 0 #Attr.12;
-    inc Json.126;
+procedure Json.102 (Json.103, Json.527, Json.101):
+    let Json.536 : I64 = 34i64;
+    let Json.535 : U8 = CallByName Num.127 Json.536;
+    let Json.533 : List U8 = CallByName List.4 Json.103 Json.535;
+    let Json.534 : List U8 = CallByName Str.12 Json.101;
+    let Json.530 : List U8 = CallByName List.8 Json.533 Json.534;
+    let Json.532 : I64 = 34i64;
+    let Json.531 : U8 = CallByName Num.127 Json.532;
+    let Json.529 : List U8 = CallByName List.4 Json.530 Json.531;
+    ret Json.529;
+
+procedure Json.144 (Json.145, Json.486, #Attr.12):
+    let Json.143 : List Str = StructAtIndex 1 #Attr.12;
+    inc Json.143;
+    let Json.142 : Str = StructAtIndex 0 #Attr.12;
+    inc Json.142;
     dec #Attr.12;
-    let Json.466 : I64 = 123i64;
-    let Json.465 : U8 = CallByName Num.127 Json.466;
-    let Json.462 : List U8 = CallByName List.4 Json.129 Json.465;
-    let Json.464 : I64 = 34i64;
-    let Json.463 : U8 = CallByName Num.127 Json.464;
-    let Json.460 : List U8 = CallByName List.4 Json.462 Json.463;
-    let Json.461 : List U8 = CallByName Str.12 Json.126;
-    let Json.457 : List U8 = CallByName List.8 Json.460 Json.461;
-    let Json.459 : I64 = 34i64;
-    let Json.458 : U8 = CallByName Num.127 Json.459;
-    let Json.454 : List U8 = CallByName List.4 Json.457 Json.458;
-    let Json.456 : I64 = 58i64;
-    let Json.455 : U8 = CallByName Num.127 Json.456;
-    let Json.451 : List U8 = CallByName List.4 Json.454 Json.455;
-    let Json.453 : I64 = 91i64;
-    let Json.452 : U8 = CallByName Num.127 Json.453;
-    let Json.131 : List U8 = CallByName List.4 Json.451 Json.452;
-    let Json.450 : U64 = CallByName List.6 Json.127;
-    let Json.438 : {List U8, U64} = Struct {Json.131, Json.450};
-    let Json.439 : {} = Struct {};
-    let Json.437 : {List U8, U64} = CallByName List.18 Json.127 Json.438 Json.439;
-    dec Json.127;
-    let Json.133 : List U8 = StructAtIndex 0 Json.437;
-    inc Json.133;
-    dec Json.437;
-    let Json.436 : I64 = 93i64;
-    let Json.435 : U8 = CallByName Num.127 Json.436;
-    let Json.432 : List U8 = CallByName List.4 Json.133 Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.431 : List U8 = CallByName List.4 Json.432 Json.433;
-    ret Json.431;
+    let Json.524 : I64 = 123i64;
+    let Json.523 : U8 = CallByName Num.127 Json.524;
+    let Json.520 : List U8 = CallByName List.4 Json.145 Json.523;
+    let Json.522 : I64 = 34i64;
+    let Json.521 : U8 = CallByName Num.127 Json.522;
+    let Json.518 : List U8 = CallByName List.4 Json.520 Json.521;
+    let Json.519 : List U8 = CallByName Str.12 Json.142;
+    let Json.515 : List U8 = CallByName List.8 Json.518 Json.519;
+    let Json.517 : I64 = 34i64;
+    let Json.516 : U8 = CallByName Num.127 Json.517;
+    let Json.512 : List U8 = CallByName List.4 Json.515 Json.516;
+    let Json.514 : I64 = 58i64;
+    let Json.513 : U8 = CallByName Num.127 Json.514;
+    let Json.509 : List U8 = CallByName List.4 Json.512 Json.513;
+    let Json.511 : I64 = 91i64;
+    let Json.510 : U8 = CallByName Num.127 Json.511;
+    let Json.147 : List U8 = CallByName List.4 Json.509 Json.510;
+    let Json.508 : U64 = CallByName List.6 Json.143;
+    let Json.496 : {List U8, U64} = Struct {Json.147, Json.508};
+    let Json.497 : {} = Struct {};
+    let Json.495 : {List U8, U64} = CallByName List.18 Json.143 Json.496 Json.497;
+    dec Json.143;
+    let Json.149 : List U8 = StructAtIndex 0 Json.495;
+    inc Json.149;
+    dec Json.495;
+    let Json.494 : I64 = 93i64;
+    let Json.493 : U8 = CallByName Num.127 Json.494;
+    let Json.490 : List U8 = CallByName List.4 Json.149 Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.489 : List U8 = CallByName List.4 Json.490 Json.491;
+    ret Json.489;
 
-procedure Json.130 (Json.430, Json.136):
-    let Json.134 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.134;
-    let Json.135 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.449 : {} = Struct {};
-    let Json.137 : List U8 = CallByName Encode.23 Json.134 Json.136 Json.449;
-    joinpoint Json.444 Json.138:
-        let Json.442 : U64 = 1i64;
-        let Json.441 : U64 = CallByName Num.20 Json.135 Json.442;
-        let Json.440 : {List U8, U64} = Struct {Json.138, Json.441};
-        ret Json.440;
+procedure Json.146 (Json.488, Json.152):
+    let Json.150 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.150;
+    let Json.151 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.507 : {} = Struct {};
+    let Json.153 : List U8 = CallByName Encode.24 Json.150 Json.152 Json.507;
+    joinpoint Json.502 Json.154:
+        let Json.500 : U64 = 1i64;
+        let Json.499 : U64 = CallByName Num.20 Json.151 Json.500;
+        let Json.498 : {List U8, U64} = Struct {Json.154, Json.499};
+        ret Json.498;
     in
-    let Json.448 : U64 = 1i64;
-    let Json.445 : Int1 = CallByName Num.24 Json.135 Json.448;
-    if Json.445 then
-        let Json.447 : I64 = 44i64;
-        let Json.446 : U8 = CallByName Num.127 Json.447;
-        let Json.443 : List U8 = CallByName List.4 Json.137 Json.446;
-        jump Json.444 Json.443;
+    let Json.506 : U64 = 1i64;
+    let Json.503 : Int1 = CallByName Num.24 Json.151 Json.506;
+    if Json.503 then
+        let Json.505 : I64 = 44i64;
+        let Json.504 : U8 = CallByName Num.127 Json.505;
+        let Json.501 : List U8 = CallByName List.4 Json.153 Json.504;
+        jump Json.502 Json.501;
     else
-        jump Json.444 Json.137;
+        jump Json.502 Json.153;
 
-procedure Json.18 (Json.97):
-    let Json.479 : Str = CallByName Encode.22 Json.97;
-    ret Json.479;
+procedure Json.18 (Json.101):
+    let Json.537 : Str = CallByName Encode.23 Json.101;
+    ret Json.537;
 
-procedure Json.21 (Json.126, Json.127):
-    let Json.427 : {Str, List Str} = Struct {Json.126, Json.127};
-    let Json.426 : {Str, List Str} = CallByName Encode.22 Json.427;
-    ret Json.426;
-
-procedure Json.98 (Json.99, Json.469, Json.97):
-    let Json.478 : I64 = 34i64;
-    let Json.477 : U8 = CallByName Num.127 Json.478;
-    let Json.475 : List U8 = CallByName List.4 Json.99 Json.477;
-    let Json.476 : List U8 = CallByName Str.12 Json.97;
-    let Json.472 : List U8 = CallByName List.8 Json.475 Json.476;
-    let Json.474 : I64 = 34i64;
-    let Json.473 : U8 = CallByName Num.127 Json.474;
-    let Json.471 : List U8 = CallByName List.4 Json.472 Json.473;
-    ret Json.471;
+procedure Json.22 (Json.142, Json.143):
+    let Json.485 : {Str, List Str} = Struct {Json.142, Json.143};
+    let Json.484 : {Str, List Str} = CallByName Encode.23 Json.485;
+    ret Json.484;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.547 : {List U8, U64} = CallByName Json.130 List.140 List.141;
+    let List.547 : {List U8, U64} = CallByName Json.146 List.140 List.141;
     ret List.547;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -242,7 +242,7 @@ procedure Test.0 ():
     let Test.12 : Str = "foo";
     let Test.1 : {Str, Str} = Struct {Test.12, Test.13};
     let Test.11 : {} = CallByName Json.1;
-    let Test.10 : List U8 = CallByName Encode.25 Test.1 Test.11;
+    let Test.10 : List U8 = CallByName Encode.26 Test.1 Test.11;
     let Test.2 : [C {U64, U8}, C Str] = CallByName Str.9 Test.10;
     let Test.7 : U8 = 1i64;
     let Test.8 : U8 = GetTagId Test.2;

crates/compiler/test_mono/generated/issue_4749.txt

@@ -28,229 +28,229 @@ procedure Bool.7 (Bool.19, Bool.20):
     let Bool.37 : Int1 = CallByName Bool.12 Bool.19 Bool.20;
     ret Bool.37;
 
-procedure Decode.23 (Decode.94):
-    ret Decode.94;
+procedure Decode.24 (Decode.101):
+    ret Decode.101;
 
-procedure Decode.24 (Decode.95, Decode.114, Decode.97):
-    let Decode.127 : {List U8, [C {}, C Str]} = CallByName Json.299 Decode.95 Decode.97;
-    ret Decode.127;
+procedure Decode.25 (Decode.102, Decode.121, Decode.104):
+    let Decode.134 : {List U8, [C {}, C Str]} = CallByName Json.315 Decode.102 Decode.104;
+    ret Decode.134;
 
-procedure Decode.25 (Decode.98, Decode.99):
-    let Decode.126 : {} = CallByName Json.42;
-    let Decode.125 : {List U8, [C {}, C Str]} = CallByName Decode.24 Decode.98 Decode.126 Decode.99;
-    ret Decode.125;
+procedure Decode.26 (Decode.105, Decode.106):
+    let Decode.133 : {} = CallByName Json.43;
+    let Decode.132 : {List U8, [C {}, C Str]} = CallByName Decode.25 Decode.105 Decode.133 Decode.106;
+    ret Decode.132;
 
-procedure Decode.26 (Decode.100, Decode.101):
-    let Decode.115 : {List U8, [C {}, C Str]} = CallByName Decode.25 Decode.100 Decode.101;
-    let Decode.103 : List U8 = StructAtIndex 0 Decode.115;
-    inc Decode.103;
-    let Decode.102 : [C {}, C Str] = StructAtIndex 1 Decode.115;
-    inc Decode.102;
-    dec Decode.115;
-    let Decode.118 : Int1 = CallByName List.1 Decode.103;
-    if Decode.118 then
-        dec Decode.103;
-        let Decode.122 : U8 = 1i64;
-        let Decode.123 : U8 = GetTagId Decode.102;
-        let Decode.124 : Int1 = lowlevel Eq Decode.122 Decode.123;
-        if Decode.124 then
-            let Decode.104 : Str = UnionAtIndex (Id 1) (Index 0) Decode.102;
-            inc Decode.104;
-            dec Decode.102;
-            let Decode.119 : [C [C List U8, C ], C Str] = TagId(1) Decode.104;
-            ret Decode.119;
+procedure Decode.27 (Decode.107, Decode.108):
+    let Decode.122 : {List U8, [C {}, C Str]} = CallByName Decode.26 Decode.107 Decode.108;
+    let Decode.110 : List U8 = StructAtIndex 0 Decode.122;
+    inc Decode.110;
+    let Decode.109 : [C {}, C Str] = StructAtIndex 1 Decode.122;
+    inc Decode.109;
+    dec Decode.122;
+    let Decode.125 : Int1 = CallByName List.1 Decode.110;
+    if Decode.125 then
+        dec Decode.110;
+        let Decode.129 : U8 = 1i64;
+        let Decode.130 : U8 = GetTagId Decode.109;
+        let Decode.131 : Int1 = lowlevel Eq Decode.129 Decode.130;
+        if Decode.131 then
+            let Decode.111 : Str = UnionAtIndex (Id 1) (Index 0) Decode.109;
+            inc Decode.111;
+            dec Decode.109;
+            let Decode.126 : [C [C List U8, C ], C Str] = TagId(1) Decode.111;
+            ret Decode.126;
         else
-            dec Decode.102;
-            let Decode.121 : [C List U8, C ] = TagId(1) ;
-            let Decode.120 : [C [C List U8, C ], C Str] = TagId(0) Decode.121;
-            ret Decode.120;
+            dec Decode.109;
+            let Decode.128 : [C List U8, C ] = TagId(1) ;
+            let Decode.127 : [C [C List U8, C ], C Str] = TagId(0) Decode.128;
+            ret Decode.127;
     else
-        dec Decode.102;
-        let Decode.117 : [C List U8, C ] = TagId(0) Decode.103;
-        let Decode.116 : [C [C List U8, C ], C Str] = TagId(0) Decode.117;
-        ret Decode.116;
+        dec Decode.109;
+        let Decode.124 : [C List U8, C ] = TagId(0) Decode.110;
+        let Decode.123 : [C [C List U8, C ], C Str] = TagId(0) Decode.124;
+        ret Decode.123;
 
-procedure Json.144 (Json.512, Json.513):
-    joinpoint Json.450 Json.447 Json.143:
-        let Json.146 : List U8 = StructAtIndex 0 Json.447;
-        inc Json.146;
-        let Json.145 : List U8 = StructAtIndex 1 Json.447;
-        inc Json.145;
-        dec Json.447;
-        joinpoint Json.490:
-            let Json.487 : {List U8, List U8} = Struct {Json.146, Json.145};
-            ret Json.487;
+procedure Json.160 (Json.570, Json.571):
+    joinpoint Json.508 Json.505 Json.159:
+        let Json.162 : List U8 = StructAtIndex 0 Json.505;
+        inc Json.162;
+        let Json.161 : List U8 = StructAtIndex 1 Json.505;
+        inc Json.161;
+        dec Json.505;
+        joinpoint Json.548:
+            let Json.545 : {List U8, List U8} = Struct {Json.162, Json.161};
+            ret Json.545;
         in
-        let Json.496 : U64 = lowlevel ListLen Json.146;
-        let Json.497 : U64 = 2i64;
-        let Json.498 : Int1 = lowlevel NumGte Json.496 Json.497;
-        if Json.498 then
-            let Json.489 : U64 = 0i64;
-            let Json.147 : U8 = lowlevel ListGetUnsafe Json.146 Json.489;
-            let Json.488 : U64 = 1i64;
-            let Json.148 : U8 = lowlevel ListGetUnsafe Json.146 Json.488;
-            let Json.458 : Int1 = CallByName Json.22 Json.147 Json.148;
-            if Json.458 then
-                let Json.465 : U64 = 2i64;
-                let Json.462 : List U8 = CallByName List.29 Json.146 Json.465;
-                let Json.464 : List U8 = CallByName List.4 Json.145 Json.147;
-                let Json.463 : List U8 = CallByName List.4 Json.464 Json.148;
-                let Json.460 : {List U8, List U8} = Struct {Json.462, Json.463};
-                jump Json.450 Json.460 Json.143;
+        let Json.554 : U64 = lowlevel ListLen Json.162;
+        let Json.555 : U64 = 2i64;
+        let Json.556 : Int1 = lowlevel NumGte Json.554 Json.555;
+        if Json.556 then
+            let Json.547 : U64 = 0i64;
+            let Json.163 : U8 = lowlevel ListGetUnsafe Json.162 Json.547;
+            let Json.546 : U64 = 1i64;
+            let Json.164 : U8 = lowlevel ListGetUnsafe Json.162 Json.546;
+            let Json.516 : Int1 = CallByName Json.23 Json.163 Json.164;
+            if Json.516 then
+                let Json.523 : U64 = 2i64;
+                let Json.520 : List U8 = CallByName List.29 Json.162 Json.523;
+                let Json.522 : List U8 = CallByName List.4 Json.161 Json.163;
+                let Json.521 : List U8 = CallByName List.4 Json.522 Json.164;
+                let Json.518 : {List U8, List U8} = Struct {Json.520, Json.521};
+                jump Json.508 Json.518 Json.159;
             else
-                let Json.452 : Int1 = CallByName Json.289 Json.147;
-                if Json.452 then
-                    let Json.456 : List U8 = CallByName List.38 Json.146;
-                    let Json.457 : List U8 = CallByName List.4 Json.145 Json.147;
-                    let Json.454 : {List U8, List U8} = Struct {Json.456, Json.457};
-                    jump Json.450 Json.454 Json.143;
+                let Json.510 : Int1 = CallByName Json.305 Json.163;
+                if Json.510 then
+                    let Json.514 : List U8 = CallByName List.38 Json.162;
+                    let Json.515 : List U8 = CallByName List.4 Json.161 Json.163;
+                    let Json.512 : {List U8, List U8} = Struct {Json.514, Json.515};
+                    jump Json.508 Json.512 Json.159;
                 else
-                    let Json.451 : {List U8, List U8} = Struct {Json.146, Json.145};
-                    ret Json.451;
+                    let Json.509 : {List U8, List U8} = Struct {Json.162, Json.161};
+                    ret Json.509;
         else
-            let Json.493 : U64 = lowlevel ListLen Json.146;
-            let Json.494 : U64 = 1i64;
-            let Json.495 : Int1 = lowlevel NumGte Json.493 Json.494;
-            if Json.495 then
-                let Json.492 : U64 = 0i64;
-                let Json.149 : U8 = lowlevel ListGetUnsafe Json.146 Json.492;
-                joinpoint Json.485 Json.491:
-                    if Json.491 then
-                        let Json.483 : List U8 = CallByName List.38 Json.146;
-                        let Json.484 : List U8 = CallByName List.4 Json.145 Json.149;
-                        let Json.481 : {List U8, List U8} = Struct {Json.483, Json.484};
-                        jump Json.450 Json.481 Json.143;
+            let Json.551 : U64 = lowlevel ListLen Json.162;
+            let Json.552 : U64 = 1i64;
+            let Json.553 : Int1 = lowlevel NumGte Json.551 Json.552;
+            if Json.553 then
+                let Json.550 : U64 = 0i64;
+                let Json.165 : U8 = lowlevel ListGetUnsafe Json.162 Json.550;
+                joinpoint Json.543 Json.549:
+                    if Json.549 then
+                        let Json.541 : List U8 = CallByName List.38 Json.162;
+                        let Json.542 : List U8 = CallByName List.4 Json.161 Json.165;
+                        let Json.539 : {List U8, List U8} = Struct {Json.541, Json.542};
+                        jump Json.508 Json.539 Json.159;
                     else
-                        jump Json.490;
+                        jump Json.548;
                 in
-                let Json.486 : Int1 = CallByName Json.289 Json.149;
-                jump Json.485 Json.486;
+                let Json.544 : Int1 = CallByName Json.305 Json.165;
+                jump Json.543 Json.544;
             else
-                jump Json.490;
+                jump Json.548;
     in
-    jump Json.450 Json.512 Json.513;
+    jump Json.508 Json.570 Json.571;
 
 procedure Json.2 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.22 (Json.139, Json.140):
-    let Json.466 : {U8, U8} = Struct {Json.139, Json.140};
-    joinpoint Json.475:
-        let Json.474 : Int1 = CallByName Bool.1;
-        ret Json.474;
+procedure Json.23 (Json.155, Json.156):
+    let Json.524 : {U8, U8} = Struct {Json.155, Json.156};
+    joinpoint Json.533:
+        let Json.532 : Int1 = CallByName Bool.1;
+        ret Json.532;
     in
-    let Json.477 : U8 = StructAtIndex 0 Json.466;
-    let Json.478 : U8 = 92i64;
-    let Json.479 : Int1 = lowlevel Eq Json.478 Json.477;
-    if Json.479 then
-        let Json.476 : U8 = StructAtIndex 1 Json.466;
-        switch Json.476:
+    let Json.535 : U8 = StructAtIndex 0 Json.524;
+    let Json.536 : U8 = 92i64;
+    let Json.537 : Int1 = lowlevel Eq Json.536 Json.535;
+    if Json.537 then
+        let Json.534 : U8 = StructAtIndex 1 Json.524;
+        switch Json.534:
             case 98:
-                let Json.467 : Int1 = CallByName Bool.2;
-                ret Json.467;
+                let Json.525 : Int1 = CallByName Bool.2;
+                ret Json.525;
         
             case 102:
-                let Json.468 : Int1 = CallByName Bool.2;
-                ret Json.468;
+                let Json.526 : Int1 = CallByName Bool.2;
+                ret Json.526;
         
             case 110:
-                let Json.469 : Int1 = CallByName Bool.2;
-                ret Json.469;
+                let Json.527 : Int1 = CallByName Bool.2;
+                ret Json.527;
         
             case 114:
-                let Json.470 : Int1 = CallByName Bool.2;
-                ret Json.470;
+                let Json.528 : Int1 = CallByName Bool.2;
+                ret Json.528;
         
             case 116:
-                let Json.471 : Int1 = CallByName Bool.2;
-                ret Json.471;
+                let Json.529 : Int1 = CallByName Bool.2;
+                ret Json.529;
         
             case 34:
-                let Json.472 : Int1 = CallByName Bool.2;
-                ret Json.472;
+                let Json.530 : Int1 = CallByName Bool.2;
+                ret Json.530;
         
             case 92:
-                let Json.473 : Int1 = CallByName Bool.2;
-                ret Json.473;
+                let Json.531 : Int1 = CallByName Bool.2;
+                ret Json.531;
         
             default:
-                jump Json.475;
+                jump Json.533;
         
     else
-        jump Json.475;
+        jump Json.533;
 
-procedure Json.23 (Json.142, Json.143):
-    let Json.500 : List U8 = Array [];
-    let Json.449 : {List U8, List U8} = Struct {Json.142, Json.500};
-    let Json.448 : {List U8, List U8} = CallByName Json.144 Json.449 Json.143;
-    ret Json.448;
+procedure Json.24 (Json.158, Json.159):
+    let Json.558 : List U8 = Array [];
+    let Json.507 : {List U8, List U8} = Struct {Json.158, Json.558};
+    let Json.506 : {List U8, List U8} = CallByName Json.160 Json.507 Json.159;
+    ret Json.506;
 
-procedure Json.289 (Json.290):
-    let Json.502 : U8 = 34i64;
-    let Json.501 : Int1 = CallByName Bool.7 Json.290 Json.502;
-    ret Json.501;
+procedure Json.305 (Json.306):
+    let Json.560 : U8 = 34i64;
+    let Json.559 : Int1 = CallByName Bool.7 Json.306 Json.560;
+    ret Json.559;
 
-procedure Json.299 (Json.300, Json.428):
-    let Json.429 : {List U8, [C {}, C Str]} = CallByName Json.41 Json.300;
-    ret Json.429;
+procedure Json.315 (Json.316, Json.486):
+    let Json.487 : {List U8, [C {}, C Str]} = CallByName Json.42 Json.316;
+    ret Json.487;
 
-procedure Json.41 (Json.282):
-    let Json.506 : U64 = 1i64;
-    inc Json.282;
-    let Json.505 : {List U8, List U8} = CallByName List.52 Json.282 Json.506;
-    let Json.283 : List U8 = StructAtIndex 0 Json.505;
-    inc Json.283;
-    let Json.285 : List U8 = StructAtIndex 1 Json.505;
-    inc Json.285;
-    dec Json.505;
-    let Json.504 : U8 = 34i64;
-    let Json.503 : List U8 = Array [Json.504];
-    let Json.433 : Int1 = CallByName Bool.11 Json.283 Json.503;
-    dec Json.503;
-    dec Json.283;
-    if Json.433 then
-        dec Json.282;
-        let Json.446 : {} = Struct {};
-        let Json.445 : {List U8, List U8} = CallByName Json.23 Json.285 Json.446;
-        let Json.288 : List U8 = StructAtIndex 0 Json.445;
-        inc Json.288;
-        let Json.287 : List U8 = StructAtIndex 1 Json.445;
-        inc Json.287;
-        dec Json.445;
-        let Json.434 : [C {U64, U8}, C Str] = CallByName Str.9 Json.287;
-        let Json.442 : U8 = 1i64;
-        let Json.443 : U8 = GetTagId Json.434;
-        let Json.444 : Int1 = lowlevel Eq Json.442 Json.443;
-        if Json.444 then
-            let Json.291 : Str = UnionAtIndex (Id 1) (Index 0) Json.434;
-            inc Json.291;
-            dec Json.434;
-            let Json.438 : U64 = 1i64;
-            let Json.437 : {List U8, List U8} = CallByName List.52 Json.288 Json.438;
-            let Json.293 : List U8 = StructAtIndex 1 Json.437;
-            inc Json.293;
-            dec Json.437;
-            let Json.436 : [C {}, C Str] = TagId(1) Json.291;
-            let Json.435 : {List U8, [C {}, C Str]} = Struct {Json.293, Json.436};
-            ret Json.435;
+procedure Json.42 (Json.298):
+    let Json.564 : U64 = 1i64;
+    inc Json.298;
+    let Json.563 : {List U8, List U8} = CallByName List.52 Json.298 Json.564;
+    let Json.299 : List U8 = StructAtIndex 0 Json.563;
+    inc Json.299;
+    let Json.301 : List U8 = StructAtIndex 1 Json.563;
+    inc Json.301;
+    dec Json.563;
+    let Json.562 : U8 = 34i64;
+    let Json.561 : List U8 = Array [Json.562];
+    let Json.491 : Int1 = CallByName Bool.11 Json.299 Json.561;
+    dec Json.561;
+    dec Json.299;
+    if Json.491 then
+        dec Json.298;
+        let Json.504 : {} = Struct {};
+        let Json.503 : {List U8, List U8} = CallByName Json.24 Json.301 Json.504;
+        let Json.304 : List U8 = StructAtIndex 0 Json.503;
+        inc Json.304;
+        let Json.303 : List U8 = StructAtIndex 1 Json.503;
+        inc Json.303;
+        dec Json.503;
+        let Json.492 : [C {U64, U8}, C Str] = CallByName Str.9 Json.303;
+        let Json.500 : U8 = 1i64;
+        let Json.501 : U8 = GetTagId Json.492;
+        let Json.502 : Int1 = lowlevel Eq Json.500 Json.501;
+        if Json.502 then
+            let Json.307 : Str = UnionAtIndex (Id 1) (Index 0) Json.492;
+            inc Json.307;
+            dec Json.492;
+            let Json.496 : U64 = 1i64;
+            let Json.495 : {List U8, List U8} = CallByName List.52 Json.304 Json.496;
+            let Json.309 : List U8 = StructAtIndex 1 Json.495;
+            inc Json.309;
+            dec Json.495;
+            let Json.494 : [C {}, C Str] = TagId(1) Json.307;
+            let Json.493 : {List U8, [C {}, C Str]} = Struct {Json.309, Json.494};
+            ret Json.493;
         else
-            dec Json.434;
-            let Json.441 : {} = Struct {};
-            let Json.440 : [C {}, C Str] = TagId(0) Json.441;
-            let Json.439 : {List U8, [C {}, C Str]} = Struct {Json.288, Json.440};
-            ret Json.439;
+            dec Json.492;
+            let Json.499 : {} = Struct {};
+            let Json.498 : [C {}, C Str] = TagId(0) Json.499;
+            let Json.497 : {List U8, [C {}, C Str]} = Struct {Json.304, Json.498};
+            ret Json.497;
     else
-        dec Json.285;
-        let Json.432 : {} = Struct {};
-        let Json.431 : [C {}, C Str] = TagId(0) Json.432;
-        let Json.430 : {List U8, [C {}, C Str]} = Struct {Json.282, Json.431};
-        ret Json.430;
+        dec Json.301;
+        let Json.490 : {} = Struct {};
+        let Json.489 : [C {}, C Str] = TagId(0) Json.490;
+        let Json.488 : {List U8, [C {}, C Str]} = Struct {Json.298, Json.489};
+        ret Json.488;
 
-procedure Json.42 ():
-    let Json.427 : {} = Struct {};
-    let Json.426 : {} = CallByName Decode.23 Json.427;
-    ret Json.426;
+procedure Json.43 ():
+    let Json.485 : {} = Struct {};
+    let Json.484 : {} = CallByName Decode.24 Json.485;
+    ret Json.484;
 
 procedure List.1 (List.95):
     let List.495 : U64 = CallByName List.6 List.95;
@@ -374,7 +374,7 @@ procedure Test.3 ():
     let Test.0 : List U8 = Array [82i64, 111i64, 99i64];
     let Test.8 : {} = CallByName Json.2;
     inc Test.0;
-    let Test.1 : [C [C List U8, C ], C Str] = CallByName Decode.26 Test.0 Test.8;
+    let Test.1 : [C [C List U8, C ], C Str] = CallByName Decode.27 Test.0 Test.8;
     let Test.7 : Str = "Roc";
     let Test.6 : [C [C List U8, C ], C Str] = TagId(1) Test.7;
     inc Test.1;

crates/compiler/test_mono/generated/issue_4772_weakened_monomorphic_destructure.txt

@@ -32,199 +32,199 @@ procedure Bool.7 (Bool.19, Bool.20):
     let Bool.37 : Int1 = CallByName Bool.12 Bool.19 Bool.20;
     ret Bool.37;
 
-procedure Decode.23 (Decode.94):
-    ret Decode.94;
+procedure Decode.24 (Decode.101):
+    ret Decode.101;
 
-procedure Decode.24 (Decode.95, Decode.114, Decode.97):
-    let Decode.117 : {List U8, [C {}, C Str]} = CallByName Json.299 Decode.95 Decode.97;
-    ret Decode.117;
+procedure Decode.25 (Decode.102, Decode.121, Decode.104):
+    let Decode.124 : {List U8, [C {}, C Str]} = CallByName Json.315 Decode.102 Decode.104;
+    ret Decode.124;
 
-procedure Decode.25 (Decode.98, Decode.99):
-    let Decode.116 : {} = CallByName Json.42;
-    let Decode.115 : {List U8, [C {}, C Str]} = CallByName Decode.24 Decode.98 Decode.116 Decode.99;
-    ret Decode.115;
+procedure Decode.26 (Decode.105, Decode.106):
+    let Decode.123 : {} = CallByName Json.43;
+    let Decode.122 : {List U8, [C {}, C Str]} = CallByName Decode.25 Decode.105 Decode.123 Decode.106;
+    ret Decode.122;
 
-procedure Json.144 (Json.512, Json.513):
-    joinpoint Json.450 Json.447 Json.143:
-        let Json.146 : List U8 = StructAtIndex 0 Json.447;
-        inc Json.146;
-        let Json.145 : List U8 = StructAtIndex 1 Json.447;
-        inc Json.145;
-        dec Json.447;
-        joinpoint Json.490:
-            let Json.487 : {List U8, List U8} = Struct {Json.146, Json.145};
-            ret Json.487;
+procedure Json.160 (Json.570, Json.571):
+    joinpoint Json.508 Json.505 Json.159:
+        let Json.162 : List U8 = StructAtIndex 0 Json.505;
+        inc Json.162;
+        let Json.161 : List U8 = StructAtIndex 1 Json.505;
+        inc Json.161;
+        dec Json.505;
+        joinpoint Json.548:
+            let Json.545 : {List U8, List U8} = Struct {Json.162, Json.161};
+            ret Json.545;
         in
-        let Json.496 : U64 = lowlevel ListLen Json.146;
-        let Json.497 : U64 = 2i64;
-        let Json.498 : Int1 = lowlevel NumGte Json.496 Json.497;
-        if Json.498 then
-            let Json.489 : U64 = 0i64;
-            let Json.147 : U8 = lowlevel ListGetUnsafe Json.146 Json.489;
-            let Json.488 : U64 = 1i64;
-            let Json.148 : U8 = lowlevel ListGetUnsafe Json.146 Json.488;
-            let Json.458 : Int1 = CallByName Json.22 Json.147 Json.148;
-            if Json.458 then
-                let Json.465 : U64 = 2i64;
-                let Json.462 : List U8 = CallByName List.29 Json.146 Json.465;
-                let Json.464 : List U8 = CallByName List.4 Json.145 Json.147;
-                let Json.463 : List U8 = CallByName List.4 Json.464 Json.148;
-                let Json.460 : {List U8, List U8} = Struct {Json.462, Json.463};
-                jump Json.450 Json.460 Json.143;
+        let Json.554 : U64 = lowlevel ListLen Json.162;
+        let Json.555 : U64 = 2i64;
+        let Json.556 : Int1 = lowlevel NumGte Json.554 Json.555;
+        if Json.556 then
+            let Json.547 : U64 = 0i64;
+            let Json.163 : U8 = lowlevel ListGetUnsafe Json.162 Json.547;
+            let Json.546 : U64 = 1i64;
+            let Json.164 : U8 = lowlevel ListGetUnsafe Json.162 Json.546;
+            let Json.516 : Int1 = CallByName Json.23 Json.163 Json.164;
+            if Json.516 then
+                let Json.523 : U64 = 2i64;
+                let Json.520 : List U8 = CallByName List.29 Json.162 Json.523;
+                let Json.522 : List U8 = CallByName List.4 Json.161 Json.163;
+                let Json.521 : List U8 = CallByName List.4 Json.522 Json.164;
+                let Json.518 : {List U8, List U8} = Struct {Json.520, Json.521};
+                jump Json.508 Json.518 Json.159;
             else
-                let Json.452 : Int1 = CallByName Json.289 Json.147;
-                if Json.452 then
-                    let Json.456 : List U8 = CallByName List.38 Json.146;
-                    let Json.457 : List U8 = CallByName List.4 Json.145 Json.147;
-                    let Json.454 : {List U8, List U8} = Struct {Json.456, Json.457};
-                    jump Json.450 Json.454 Json.143;
+                let Json.510 : Int1 = CallByName Json.305 Json.163;
+                if Json.510 then
+                    let Json.514 : List U8 = CallByName List.38 Json.162;
+                    let Json.515 : List U8 = CallByName List.4 Json.161 Json.163;
+                    let Json.512 : {List U8, List U8} = Struct {Json.514, Json.515};
+                    jump Json.508 Json.512 Json.159;
                 else
-                    let Json.451 : {List U8, List U8} = Struct {Json.146, Json.145};
-                    ret Json.451;
+                    let Json.509 : {List U8, List U8} = Struct {Json.162, Json.161};
+                    ret Json.509;
         else
-            let Json.493 : U64 = lowlevel ListLen Json.146;
-            let Json.494 : U64 = 1i64;
-            let Json.495 : Int1 = lowlevel NumGte Json.493 Json.494;
-            if Json.495 then
-                let Json.492 : U64 = 0i64;
-                let Json.149 : U8 = lowlevel ListGetUnsafe Json.146 Json.492;
-                joinpoint Json.485 Json.491:
-                    if Json.491 then
-                        let Json.483 : List U8 = CallByName List.38 Json.146;
-                        let Json.484 : List U8 = CallByName List.4 Json.145 Json.149;
-                        let Json.481 : {List U8, List U8} = Struct {Json.483, Json.484};
-                        jump Json.450 Json.481 Json.143;
+            let Json.551 : U64 = lowlevel ListLen Json.162;
+            let Json.552 : U64 = 1i64;
+            let Json.553 : Int1 = lowlevel NumGte Json.551 Json.552;
+            if Json.553 then
+                let Json.550 : U64 = 0i64;
+                let Json.165 : U8 = lowlevel ListGetUnsafe Json.162 Json.550;
+                joinpoint Json.543 Json.549:
+                    if Json.549 then
+                        let Json.541 : List U8 = CallByName List.38 Json.162;
+                        let Json.542 : List U8 = CallByName List.4 Json.161 Json.165;
+                        let Json.539 : {List U8, List U8} = Struct {Json.541, Json.542};
+                        jump Json.508 Json.539 Json.159;
                     else
-                        jump Json.490;
+                        jump Json.548;
                 in
-                let Json.486 : Int1 = CallByName Json.289 Json.149;
-                jump Json.485 Json.486;
+                let Json.544 : Int1 = CallByName Json.305 Json.165;
+                jump Json.543 Json.544;
             else
-                jump Json.490;
+                jump Json.548;
     in
-    jump Json.450 Json.512 Json.513;
+    jump Json.508 Json.570 Json.571;
 
 procedure Json.2 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.22 (Json.139, Json.140):
-    let Json.466 : {U8, U8} = Struct {Json.139, Json.140};
-    joinpoint Json.475:
-        let Json.474 : Int1 = CallByName Bool.1;
-        ret Json.474;
+procedure Json.23 (Json.155, Json.156):
+    let Json.524 : {U8, U8} = Struct {Json.155, Json.156};
+    joinpoint Json.533:
+        let Json.532 : Int1 = CallByName Bool.1;
+        ret Json.532;
     in
-    let Json.477 : U8 = StructAtIndex 0 Json.466;
-    let Json.478 : U8 = 92i64;
-    let Json.479 : Int1 = lowlevel Eq Json.478 Json.477;
-    if Json.479 then
-        let Json.476 : U8 = StructAtIndex 1 Json.466;
-        switch Json.476:
+    let Json.535 : U8 = StructAtIndex 0 Json.524;
+    let Json.536 : U8 = 92i64;
+    let Json.537 : Int1 = lowlevel Eq Json.536 Json.535;
+    if Json.537 then
+        let Json.534 : U8 = StructAtIndex 1 Json.524;
+        switch Json.534:
             case 98:
-                let Json.467 : Int1 = CallByName Bool.2;
-                ret Json.467;
+                let Json.525 : Int1 = CallByName Bool.2;
+                ret Json.525;
         
             case 102:
-                let Json.468 : Int1 = CallByName Bool.2;
-                ret Json.468;
+                let Json.526 : Int1 = CallByName Bool.2;
+                ret Json.526;
         
             case 110:
-                let Json.469 : Int1 = CallByName Bool.2;
-                ret Json.469;
+                let Json.527 : Int1 = CallByName Bool.2;
+                ret Json.527;
         
             case 114:
-                let Json.470 : Int1 = CallByName Bool.2;
-                ret Json.470;
+                let Json.528 : Int1 = CallByName Bool.2;
+                ret Json.528;
         
             case 116:
-                let Json.471 : Int1 = CallByName Bool.2;
-                ret Json.471;
+                let Json.529 : Int1 = CallByName Bool.2;
+                ret Json.529;
         
             case 34:
-                let Json.472 : Int1 = CallByName Bool.2;
-                ret Json.472;
+                let Json.530 : Int1 = CallByName Bool.2;
+                ret Json.530;
         
             case 92:
-                let Json.473 : Int1 = CallByName Bool.2;
-                ret Json.473;
+                let Json.531 : Int1 = CallByName Bool.2;
+                ret Json.531;
         
             default:
-                jump Json.475;
+                jump Json.533;
         
     else
-        jump Json.475;
+        jump Json.533;
 
-procedure Json.23 (Json.142, Json.143):
-    let Json.500 : List U8 = Array [];
-    let Json.449 : {List U8, List U8} = Struct {Json.142, Json.500};
-    let Json.448 : {List U8, List U8} = CallByName Json.144 Json.449 Json.143;
-    ret Json.448;
+procedure Json.24 (Json.158, Json.159):
+    let Json.558 : List U8 = Array [];
+    let Json.507 : {List U8, List U8} = Struct {Json.158, Json.558};
+    let Json.506 : {List U8, List U8} = CallByName Json.160 Json.507 Json.159;
+    ret Json.506;
 
-procedure Json.289 (Json.290):
-    let Json.502 : U8 = 34i64;
-    let Json.501 : Int1 = CallByName Bool.7 Json.290 Json.502;
-    ret Json.501;
+procedure Json.305 (Json.306):
+    let Json.560 : U8 = 34i64;
+    let Json.559 : Int1 = CallByName Bool.7 Json.306 Json.560;
+    ret Json.559;
 
-procedure Json.299 (Json.300, Json.428):
-    let Json.429 : {List U8, [C {}, C Str]} = CallByName Json.41 Json.300;
-    ret Json.429;
+procedure Json.315 (Json.316, Json.486):
+    let Json.487 : {List U8, [C {}, C Str]} = CallByName Json.42 Json.316;
+    ret Json.487;
 
-procedure Json.41 (Json.282):
-    let Json.506 : U64 = 1i64;
-    inc Json.282;
-    let Json.505 : {List U8, List U8} = CallByName List.52 Json.282 Json.506;
-    let Json.283 : List U8 = StructAtIndex 0 Json.505;
-    inc Json.283;
-    let Json.285 : List U8 = StructAtIndex 1 Json.505;
-    inc Json.285;
-    dec Json.505;
-    let Json.504 : U8 = 34i64;
-    let Json.503 : List U8 = Array [Json.504];
-    let Json.433 : Int1 = CallByName Bool.11 Json.283 Json.503;
-    dec Json.503;
-    dec Json.283;
-    if Json.433 then
-        dec Json.282;
-        let Json.446 : {} = Struct {};
-        let Json.445 : {List U8, List U8} = CallByName Json.23 Json.285 Json.446;
-        let Json.288 : List U8 = StructAtIndex 0 Json.445;
-        inc Json.288;
-        let Json.287 : List U8 = StructAtIndex 1 Json.445;
-        inc Json.287;
-        dec Json.445;
-        let Json.434 : [C {U64, U8}, C Str] = CallByName Str.9 Json.287;
-        let Json.442 : U8 = 1i64;
-        let Json.443 : U8 = GetTagId Json.434;
-        let Json.444 : Int1 = lowlevel Eq Json.442 Json.443;
-        if Json.444 then
-            let Json.291 : Str = UnionAtIndex (Id 1) (Index 0) Json.434;
-            inc Json.291;
-            dec Json.434;
-            let Json.438 : U64 = 1i64;
-            let Json.437 : {List U8, List U8} = CallByName List.52 Json.288 Json.438;
-            let Json.293 : List U8 = StructAtIndex 1 Json.437;
-            inc Json.293;
-            dec Json.437;
-            let Json.436 : [C {}, C Str] = TagId(1) Json.291;
-            let Json.435 : {List U8, [C {}, C Str]} = Struct {Json.293, Json.436};
-            ret Json.435;
+procedure Json.42 (Json.298):
+    let Json.564 : U64 = 1i64;
+    inc Json.298;
+    let Json.563 : {List U8, List U8} = CallByName List.52 Json.298 Json.564;
+    let Json.299 : List U8 = StructAtIndex 0 Json.563;
+    inc Json.299;
+    let Json.301 : List U8 = StructAtIndex 1 Json.563;
+    inc Json.301;
+    dec Json.563;
+    let Json.562 : U8 = 34i64;
+    let Json.561 : List U8 = Array [Json.562];
+    let Json.491 : Int1 = CallByName Bool.11 Json.299 Json.561;
+    dec Json.561;
+    dec Json.299;
+    if Json.491 then
+        dec Json.298;
+        let Json.504 : {} = Struct {};
+        let Json.503 : {List U8, List U8} = CallByName Json.24 Json.301 Json.504;
+        let Json.304 : List U8 = StructAtIndex 0 Json.503;
+        inc Json.304;
+        let Json.303 : List U8 = StructAtIndex 1 Json.503;
+        inc Json.303;
+        dec Json.503;
+        let Json.492 : [C {U64, U8}, C Str] = CallByName Str.9 Json.303;
+        let Json.500 : U8 = 1i64;
+        let Json.501 : U8 = GetTagId Json.492;
+        let Json.502 : Int1 = lowlevel Eq Json.500 Json.501;
+        if Json.502 then
+            let Json.307 : Str = UnionAtIndex (Id 1) (Index 0) Json.492;
+            inc Json.307;
+            dec Json.492;
+            let Json.496 : U64 = 1i64;
+            let Json.495 : {List U8, List U8} = CallByName List.52 Json.304 Json.496;
+            let Json.309 : List U8 = StructAtIndex 1 Json.495;
+            inc Json.309;
+            dec Json.495;
+            let Json.494 : [C {}, C Str] = TagId(1) Json.307;
+            let Json.493 : {List U8, [C {}, C Str]} = Struct {Json.309, Json.494};
+            ret Json.493;
         else
-            dec Json.434;
-            let Json.441 : {} = Struct {};
-            let Json.440 : [C {}, C Str] = TagId(0) Json.441;
-            let Json.439 : {List U8, [C {}, C Str]} = Struct {Json.288, Json.440};
-            ret Json.439;
+            dec Json.492;
+            let Json.499 : {} = Struct {};
+            let Json.498 : [C {}, C Str] = TagId(0) Json.499;
+            let Json.497 : {List U8, [C {}, C Str]} = Struct {Json.304, Json.498};
+            ret Json.497;
     else
-        dec Json.285;
-        let Json.432 : {} = Struct {};
-        let Json.431 : [C {}, C Str] = TagId(0) Json.432;
-        let Json.430 : {List U8, [C {}, C Str]} = Struct {Json.282, Json.431};
-        ret Json.430;
+        dec Json.301;
+        let Json.490 : {} = Struct {};
+        let Json.489 : [C {}, C Str] = TagId(0) Json.490;
+        let Json.488 : {List U8, [C {}, C Str]} = Struct {Json.298, Json.489};
+        ret Json.488;
 
-procedure Json.42 ():
-    let Json.427 : {} = Struct {};
-    let Json.426 : {} = CallByName Decode.23 Json.427;
-    ret Json.426;
+procedure Json.43 ():
+    let Json.485 : {} = Struct {};
+    let Json.484 : {} = CallByName Decode.24 Json.485;
+    ret Json.484;
 
 procedure List.29 (List.298, List.299):
     let List.543 : U64 = CallByName List.6 List.298;
@@ -368,7 +368,7 @@ procedure Test.0 ():
     let Test.37 : Str = "-1234";
     let Test.35 : List U8 = CallByName Str.12 Test.37;
     let Test.36 : {} = CallByName Json.2;
-    let Test.34 : {List U8, [C {}, C Str]} = CallByName Decode.25 Test.35 Test.36;
+    let Test.34 : {List U8, [C {}, C Str]} = CallByName Decode.26 Test.35 Test.36;
     let Test.2 : List U8 = StructAtIndex 0 Test.34;
     inc Test.2;
     let Test.1 : [C {}, C Str] = StructAtIndex 1 Test.34;

crates/compiler/test_mono/generated/unspecialized_lambda_set_unification_does_not_duplicate_identical_concrete_types.txt

@@ -2,121 +2,121 @@ procedure Bool.2 ():
     let Bool.23 : Int1 = true;
     ret Bool.23;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName Test.5 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName Test.5 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.128 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
-
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.118 : List U8 = CallByName Json.98 Encode.94 Encode.96 Encode.102;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.144 Encode.99 Encode.101 Encode.107;
     ret Encode.118;
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : {Str, Str} = CallByName Test.2 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.123 : List U8 = CallByName Json.102 Encode.99 Encode.101 Encode.107;
+    ret Encode.123;
+
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : {Str, Str} = CallByName Test.2 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.128 (Json.129, Json.428, #Attr.12):
-    let Json.127 : List Str = StructAtIndex 1 #Attr.12;
-    inc Json.127;
-    let Json.126 : Str = StructAtIndex 0 #Attr.12;
-    inc Json.126;
+procedure Json.102 (Json.103, Json.530, Json.101):
+    let Json.539 : I64 = 34i64;
+    let Json.538 : U8 = CallByName Num.127 Json.539;
+    let Json.536 : List U8 = CallByName List.4 Json.103 Json.538;
+    let Json.537 : List U8 = CallByName Str.12 Json.101;
+    let Json.533 : List U8 = CallByName List.8 Json.536 Json.537;
+    let Json.535 : I64 = 34i64;
+    let Json.534 : U8 = CallByName Num.127 Json.535;
+    let Json.532 : List U8 = CallByName List.4 Json.533 Json.534;
+    ret Json.532;
+
+procedure Json.144 (Json.145, Json.486, #Attr.12):
+    let Json.143 : List Str = StructAtIndex 1 #Attr.12;
+    inc Json.143;
+    let Json.142 : Str = StructAtIndex 0 #Attr.12;
+    inc Json.142;
     dec #Attr.12;
-    let Json.466 : I64 = 123i64;
-    let Json.465 : U8 = CallByName Num.127 Json.466;
-    let Json.462 : List U8 = CallByName List.4 Json.129 Json.465;
-    let Json.464 : I64 = 34i64;
-    let Json.463 : U8 = CallByName Num.127 Json.464;
-    let Json.460 : List U8 = CallByName List.4 Json.462 Json.463;
-    let Json.461 : List U8 = CallByName Str.12 Json.126;
-    let Json.457 : List U8 = CallByName List.8 Json.460 Json.461;
-    let Json.459 : I64 = 34i64;
-    let Json.458 : U8 = CallByName Num.127 Json.459;
-    let Json.454 : List U8 = CallByName List.4 Json.457 Json.458;
-    let Json.456 : I64 = 58i64;
-    let Json.455 : U8 = CallByName Num.127 Json.456;
-    let Json.451 : List U8 = CallByName List.4 Json.454 Json.455;
-    let Json.453 : I64 = 91i64;
-    let Json.452 : U8 = CallByName Num.127 Json.453;
-    let Json.131 : List U8 = CallByName List.4 Json.451 Json.452;
-    let Json.450 : U64 = CallByName List.6 Json.127;
-    let Json.438 : {List U8, U64} = Struct {Json.131, Json.450};
-    let Json.439 : {} = Struct {};
-    let Json.437 : {List U8, U64} = CallByName List.18 Json.127 Json.438 Json.439;
-    dec Json.127;
-    let Json.133 : List U8 = StructAtIndex 0 Json.437;
-    inc Json.133;
-    dec Json.437;
-    let Json.436 : I64 = 93i64;
-    let Json.435 : U8 = CallByName Num.127 Json.436;
-    let Json.432 : List U8 = CallByName List.4 Json.133 Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.431 : List U8 = CallByName List.4 Json.432 Json.433;
-    ret Json.431;
+    let Json.524 : I64 = 123i64;
+    let Json.523 : U8 = CallByName Num.127 Json.524;
+    let Json.520 : List U8 = CallByName List.4 Json.145 Json.523;
+    let Json.522 : I64 = 34i64;
+    let Json.521 : U8 = CallByName Num.127 Json.522;
+    let Json.518 : List U8 = CallByName List.4 Json.520 Json.521;
+    let Json.519 : List U8 = CallByName Str.12 Json.142;
+    let Json.515 : List U8 = CallByName List.8 Json.518 Json.519;
+    let Json.517 : I64 = 34i64;
+    let Json.516 : U8 = CallByName Num.127 Json.517;
+    let Json.512 : List U8 = CallByName List.4 Json.515 Json.516;
+    let Json.514 : I64 = 58i64;
+    let Json.513 : U8 = CallByName Num.127 Json.514;
+    let Json.509 : List U8 = CallByName List.4 Json.512 Json.513;
+    let Json.511 : I64 = 91i64;
+    let Json.510 : U8 = CallByName Num.127 Json.511;
+    let Json.147 : List U8 = CallByName List.4 Json.509 Json.510;
+    let Json.508 : U64 = CallByName List.6 Json.143;
+    let Json.496 : {List U8, U64} = Struct {Json.147, Json.508};
+    let Json.497 : {} = Struct {};
+    let Json.495 : {List U8, U64} = CallByName List.18 Json.143 Json.496 Json.497;
+    dec Json.143;
+    let Json.149 : List U8 = StructAtIndex 0 Json.495;
+    inc Json.149;
+    dec Json.495;
+    let Json.494 : I64 = 93i64;
+    let Json.493 : U8 = CallByName Num.127 Json.494;
+    let Json.490 : List U8 = CallByName List.4 Json.149 Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.489 : List U8 = CallByName List.4 Json.490 Json.491;
+    ret Json.489;
 
-procedure Json.130 (Json.430, Json.136):
-    let Json.134 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.134;
-    let Json.135 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.449 : {} = Struct {};
-    let Json.137 : List U8 = CallByName Encode.23 Json.134 Json.136 Json.449;
-    joinpoint Json.444 Json.138:
-        let Json.442 : U64 = 1i64;
-        let Json.441 : U64 = CallByName Num.20 Json.135 Json.442;
-        let Json.440 : {List U8, U64} = Struct {Json.138, Json.441};
-        ret Json.440;
+procedure Json.146 (Json.488, Json.152):
+    let Json.150 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.150;
+    let Json.151 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.507 : {} = Struct {};
+    let Json.153 : List U8 = CallByName Encode.24 Json.150 Json.152 Json.507;
+    joinpoint Json.502 Json.154:
+        let Json.500 : U64 = 1i64;
+        let Json.499 : U64 = CallByName Num.20 Json.151 Json.500;
+        let Json.498 : {List U8, U64} = Struct {Json.154, Json.499};
+        ret Json.498;
     in
-    let Json.448 : U64 = 1i64;
-    let Json.445 : Int1 = CallByName Num.24 Json.135 Json.448;
-    if Json.445 then
-        let Json.447 : I64 = 44i64;
-        let Json.446 : U8 = CallByName Num.127 Json.447;
-        let Json.443 : List U8 = CallByName List.4 Json.137 Json.446;
-        jump Json.444 Json.443;
+    let Json.506 : U64 = 1i64;
+    let Json.503 : Int1 = CallByName Num.24 Json.151 Json.506;
+    if Json.503 then
+        let Json.505 : I64 = 44i64;
+        let Json.504 : U8 = CallByName Num.127 Json.505;
+        let Json.501 : List U8 = CallByName List.4 Json.153 Json.504;
+        jump Json.502 Json.501;
     else
-        jump Json.444 Json.137;
+        jump Json.502 Json.153;
 
-procedure Json.18 (Json.97):
-    let Json.482 : Str = CallByName Encode.22 Json.97;
-    ret Json.482;
+procedure Json.18 (Json.101):
+    let Json.540 : Str = CallByName Encode.23 Json.101;
+    ret Json.540;
 
-procedure Json.21 (Json.126, Json.127):
-    let Json.468 : {Str, List Str} = Struct {Json.126, Json.127};
-    let Json.467 : {Str, List Str} = CallByName Encode.22 Json.468;
-    ret Json.467;
-
-procedure Json.98 (Json.99, Json.472, Json.97):
-    let Json.481 : I64 = 34i64;
-    let Json.480 : U8 = CallByName Num.127 Json.481;
-    let Json.478 : List U8 = CallByName List.4 Json.99 Json.480;
-    let Json.479 : List U8 = CallByName Str.12 Json.97;
-    let Json.475 : List U8 = CallByName List.8 Json.478 Json.479;
-    let Json.477 : I64 = 34i64;
-    let Json.476 : U8 = CallByName Num.127 Json.477;
-    let Json.474 : List U8 = CallByName List.4 Json.475 Json.476;
-    ret Json.474;
+procedure Json.22 (Json.142, Json.143):
+    let Json.526 : {Str, List Str} = Struct {Json.142, Json.143};
+    let Json.525 : {Str, List Str} = CallByName Encode.23 Json.526;
+    ret Json.525;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.545 : {List U8, U64} = CallByName Json.130 List.140 List.141;
+    let List.545 : {List U8, U64} = CallByName Json.146 List.140 List.141;
     ret List.545;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -194,7 +194,7 @@ procedure Str.12 (#Attr.2):
     ret Str.267;
 
 procedure Test.2 (Test.10):
-    let Test.15 : {Str, Str} = CallByName Encode.22 Test.10;
+    let Test.15 : {Str, Str} = CallByName Encode.23 Test.10;
     ret Test.15;
 
 procedure Test.3 ():
@@ -205,7 +205,7 @@ procedure Test.3 ():
 
 procedure Test.5 (Test.6, Test.7, Test.4):
     joinpoint Test.20 Test.8:
-        let Test.18 : List U8 = CallByName Encode.23 Test.6 Test.8 Test.7;
+        let Test.18 : List U8 = CallByName Encode.24 Test.6 Test.8 Test.7;
         ret Test.18;
     in
     let Test.25 : Int1 = CallByName Bool.2;
@@ -216,7 +216,7 @@ procedure Test.5 (Test.6, Test.7, Test.4):
         dec Test.4;
         let Test.28 : Str = CallByName Json.18 Test.29;
         let Test.27 : List Str = Array [Test.28];
-        let Test.19 : {Str, List Str} = CallByName Json.21 Test.26 Test.27;
+        let Test.19 : {Str, List Str} = CallByName Json.22 Test.26 Test.27;
         jump Test.20 Test.19;
     else
         let Test.21 : Str = "B";
@@ -225,11 +225,11 @@ procedure Test.5 (Test.6, Test.7, Test.4):
         dec Test.4;
         let Test.23 : Str = CallByName Json.18 Test.24;
         let Test.22 : List Str = Array [Test.23];
-        let Test.19 : {Str, List Str} = CallByName Json.21 Test.21 Test.22;
+        let Test.19 : {Str, List Str} = CallByName Json.22 Test.21 Test.22;
         jump Test.20 Test.19;
 
 procedure Test.0 ():
     let Test.12 : {Str, Str} = CallByName Test.3;
     let Test.13 : {} = CallByName Json.1;
-    let Test.11 : List U8 = CallByName Encode.25 Test.12 Test.13;
+    let Test.11 : List U8 = CallByName Encode.26 Test.12 Test.13;
     ret Test.11;

crates/compiler/test_mono/generated/unspecialized_lambda_set_unification_keeps_all_concrete_types_without_unification_of_unifiable.txt

@@ -1,230 +1,230 @@
 procedure #Derived.0 (#Derived.1):
     let #Derived_gen.10 : [C {}, C {}] = TagId(0) #Derived.1;
-    let #Derived_gen.9 : [C {}, C {}] = CallByName Encode.22 #Derived_gen.10;
+    let #Derived_gen.9 : [C {}, C {}] = CallByName Encode.23 #Derived_gen.10;
     ret #Derived_gen.9;
 
 procedure #Derived.2 (#Derived.3, #Derived.4, #Attr.12):
     let #Derived.1 : {} = UnionAtIndex (Id 0) (Index 0) #Attr.12;
     joinpoint #Derived_gen.14 #Derived_gen.13:
-        let #Derived_gen.12 : List U8 = CallByName Encode.23 #Derived.3 #Derived_gen.13 #Derived.4;
+        let #Derived_gen.12 : List U8 = CallByName Encode.24 #Derived.3 #Derived_gen.13 #Derived.4;
         ret #Derived_gen.12;
     in
     let #Derived_gen.16 : Str = "A";
     let #Derived_gen.17 : List [] = Array [];
-    let #Derived_gen.15 : {Str, List []} = CallByName Json.21 #Derived_gen.16 #Derived_gen.17;
+    let #Derived_gen.15 : {Str, List []} = CallByName Json.22 #Derived_gen.16 #Derived_gen.17;
     jump #Derived_gen.14 #Derived_gen.15;
 
 procedure #Derived.5 (#Derived.6):
     let #Derived_gen.1 : [C {}, C {}] = TagId(1) #Derived.6;
-    let #Derived_gen.0 : [C {}, C {}] = CallByName Encode.22 #Derived_gen.1;
+    let #Derived_gen.0 : [C {}, C {}] = CallByName Encode.23 #Derived_gen.1;
     ret #Derived_gen.0;
 
 procedure #Derived.7 (#Derived.8, #Derived.9, #Attr.12):
     let #Derived.6 : {} = UnionAtIndex (Id 1) (Index 0) #Attr.12;
     joinpoint #Derived_gen.5 #Derived_gen.4:
-        let #Derived_gen.3 : List U8 = CallByName Encode.23 #Derived.8 #Derived_gen.4 #Derived.9;
+        let #Derived_gen.3 : List U8 = CallByName Encode.24 #Derived.8 #Derived_gen.4 #Derived.9;
         ret #Derived_gen.3;
     in
     let #Derived_gen.7 : Str = "B";
     let #Derived_gen.8 : List [] = Array [];
-    let #Derived_gen.6 : {Str, List []} = CallByName Json.21 #Derived_gen.7 #Derived_gen.8;
+    let #Derived_gen.6 : {Str, List []} = CallByName Json.22 #Derived_gen.7 #Derived_gen.8;
     jump #Derived_gen.5 #Derived_gen.6;
 
 procedure Bool.2 ():
     let Bool.23 : Int1 = true;
     ret Bool.23;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.22 (Encode.93):
-    ret Encode.93;
+procedure Encode.23 (Encode.98):
+    ret Encode.98;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.106 : List U8 = CallByName Test.5 Encode.94 Encode.96 Encode.102;
-    ret Encode.106;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.111 : List U8 = CallByName Test.5 Encode.99 Encode.101 Encode.107;
+    ret Encode.111;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.113 : List U8 = CallByName Json.128 Encode.94 Encode.96 Encode.102;
-    ret Encode.113;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.118 : List U8 = CallByName Json.144 Encode.99 Encode.101 Encode.107;
+    ret Encode.118;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.117 : U8 = GetTagId Encode.102;
-    switch Encode.117:
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.122 : U8 = GetTagId Encode.107;
+    switch Encode.122:
         case 0:
-            let Encode.116 : List U8 = CallByName #Derived.2 Encode.94 Encode.96 Encode.102;
-            ret Encode.116;
+            let Encode.121 : List U8 = CallByName #Derived.2 Encode.99 Encode.101 Encode.107;
+            ret Encode.121;
     
         default:
-            let Encode.116 : List U8 = CallByName #Derived.7 Encode.94 Encode.96 Encode.102;
-            ret Encode.116;
+            let Encode.121 : List U8 = CallByName #Derived.7 Encode.99 Encode.101 Encode.107;
+            ret Encode.121;
     
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.129 : List U8 = CallByName Json.128 Encode.94 Encode.96 Encode.102;
-    ret Encode.129;
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.134 : List U8 = CallByName Json.144 Encode.99 Encode.101 Encode.107;
+    ret Encode.134;
 
-procedure Encode.23 (Encode.94, Encode.102, Encode.96):
-    let Encode.133 : Str = "a Lambda Set is empty. Most likely there is a type error in your program.";
-    Crash Encode.133
+procedure Encode.24 (Encode.99, Encode.107, Encode.101):
+    let Encode.138 : Str = "a Lambda Set is empty. Most likely there is a type error in your program.";
+    Crash Encode.138
 
-procedure Encode.25 (Encode.100, Encode.101):
-    let Encode.104 : List U8 = Array [];
-    let Encode.105 : {{}, {}} = CallByName Test.2 Encode.100;
-    let Encode.103 : List U8 = CallByName Encode.23 Encode.104 Encode.105 Encode.101;
-    ret Encode.103;
+procedure Encode.26 (Encode.105, Encode.106):
+    let Encode.109 : List U8 = Array [];
+    let Encode.110 : {{}, {}} = CallByName Test.2 Encode.105;
+    let Encode.108 : List U8 = CallByName Encode.24 Encode.109 Encode.110 Encode.106;
+    ret Encode.108;
 
 procedure Json.1 ():
-    let Json.425 : {} = Struct {};
-    ret Json.425;
+    let Json.483 : {} = Struct {};
+    ret Json.483;
 
-procedure Json.128 (Json.129, Json.428, #Attr.12):
-    let Json.127 : List [C {}, C {}] = StructAtIndex 1 #Attr.12;
-    inc Json.127;
-    let Json.126 : Str = StructAtIndex 0 #Attr.12;
-    inc Json.126;
+procedure Json.144 (Json.145, Json.486, #Attr.12):
+    let Json.143 : List [C {}, C {}] = StructAtIndex 1 #Attr.12;
+    inc Json.143;
+    let Json.142 : Str = StructAtIndex 0 #Attr.12;
+    inc Json.142;
     dec #Attr.12;
-    let Json.466 : I64 = 123i64;
-    let Json.465 : U8 = CallByName Num.127 Json.466;
-    let Json.462 : List U8 = CallByName List.4 Json.129 Json.465;
-    let Json.464 : I64 = 34i64;
-    let Json.463 : U8 = CallByName Num.127 Json.464;
-    let Json.460 : List U8 = CallByName List.4 Json.462 Json.463;
-    let Json.461 : List U8 = CallByName Str.12 Json.126;
-    let Json.457 : List U8 = CallByName List.8 Json.460 Json.461;
-    let Json.459 : I64 = 34i64;
-    let Json.458 : U8 = CallByName Num.127 Json.459;
-    let Json.454 : List U8 = CallByName List.4 Json.457 Json.458;
-    let Json.456 : I64 = 58i64;
-    let Json.455 : U8 = CallByName Num.127 Json.456;
-    let Json.451 : List U8 = CallByName List.4 Json.454 Json.455;
-    let Json.453 : I64 = 91i64;
-    let Json.452 : U8 = CallByName Num.127 Json.453;
-    let Json.131 : List U8 = CallByName List.4 Json.451 Json.452;
-    let Json.450 : U64 = CallByName List.6 Json.127;
-    let Json.438 : {List U8, U64} = Struct {Json.131, Json.450};
-    let Json.439 : {} = Struct {};
-    let Json.437 : {List U8, U64} = CallByName List.18 Json.127 Json.438 Json.439;
-    dec Json.127;
-    let Json.133 : List U8 = StructAtIndex 0 Json.437;
-    inc Json.133;
-    dec Json.437;
-    let Json.436 : I64 = 93i64;
-    let Json.435 : U8 = CallByName Num.127 Json.436;
-    let Json.432 : List U8 = CallByName List.4 Json.133 Json.435;
-    let Json.434 : I64 = 125i64;
-    let Json.433 : U8 = CallByName Num.127 Json.434;
-    let Json.431 : List U8 = CallByName List.4 Json.432 Json.433;
-    ret Json.431;
-
-procedure Json.128 (Json.129, Json.428, #Attr.12):
-    let Json.127 : List [] = StructAtIndex 1 #Attr.12;
-    inc Json.127;
-    let Json.126 : Str = StructAtIndex 0 #Attr.12;
-    inc Json.126;
-    dec #Attr.12;
-    let Json.516 : I64 = 123i64;
-    let Json.515 : U8 = CallByName Num.127 Json.516;
-    let Json.512 : List U8 = CallByName List.4 Json.129 Json.515;
-    let Json.514 : I64 = 34i64;
+    let Json.524 : I64 = 123i64;
+    let Json.523 : U8 = CallByName Num.127 Json.524;
+    let Json.520 : List U8 = CallByName List.4 Json.145 Json.523;
+    let Json.522 : I64 = 34i64;
+    let Json.521 : U8 = CallByName Num.127 Json.522;
+    let Json.518 : List U8 = CallByName List.4 Json.520 Json.521;
+    let Json.519 : List U8 = CallByName Str.12 Json.142;
+    let Json.515 : List U8 = CallByName List.8 Json.518 Json.519;
+    let Json.517 : I64 = 34i64;
+    let Json.516 : U8 = CallByName Num.127 Json.517;
+    let Json.512 : List U8 = CallByName List.4 Json.515 Json.516;
+    let Json.514 : I64 = 58i64;
     let Json.513 : U8 = CallByName Num.127 Json.514;
-    let Json.510 : List U8 = CallByName List.4 Json.512 Json.513;
-    let Json.511 : List U8 = CallByName Str.12 Json.126;
-    let Json.507 : List U8 = CallByName List.8 Json.510 Json.511;
-    let Json.509 : I64 = 34i64;
-    let Json.508 : U8 = CallByName Num.127 Json.509;
-    let Json.504 : List U8 = CallByName List.4 Json.507 Json.508;
-    let Json.506 : I64 = 58i64;
-    let Json.505 : U8 = CallByName Num.127 Json.506;
-    let Json.501 : List U8 = CallByName List.4 Json.504 Json.505;
-    let Json.503 : I64 = 91i64;
-    let Json.502 : U8 = CallByName Num.127 Json.503;
-    let Json.131 : List U8 = CallByName List.4 Json.501 Json.502;
-    let Json.500 : U64 = CallByName List.6 Json.127;
-    let Json.488 : {List U8, U64} = Struct {Json.131, Json.500};
-    let Json.489 : {} = Struct {};
-    let Json.487 : {List U8, U64} = CallByName List.18 Json.127 Json.488 Json.489;
-    dec Json.127;
-    let Json.133 : List U8 = StructAtIndex 0 Json.487;
-    inc Json.133;
-    dec Json.487;
-    let Json.486 : I64 = 93i64;
-    let Json.485 : U8 = CallByName Num.127 Json.486;
-    let Json.482 : List U8 = CallByName List.4 Json.133 Json.485;
-    let Json.484 : I64 = 125i64;
-    let Json.483 : U8 = CallByName Num.127 Json.484;
-    let Json.481 : List U8 = CallByName List.4 Json.482 Json.483;
-    ret Json.481;
+    let Json.509 : List U8 = CallByName List.4 Json.512 Json.513;
+    let Json.511 : I64 = 91i64;
+    let Json.510 : U8 = CallByName Num.127 Json.511;
+    let Json.147 : List U8 = CallByName List.4 Json.509 Json.510;
+    let Json.508 : U64 = CallByName List.6 Json.143;
+    let Json.496 : {List U8, U64} = Struct {Json.147, Json.508};
+    let Json.497 : {} = Struct {};
+    let Json.495 : {List U8, U64} = CallByName List.18 Json.143 Json.496 Json.497;
+    dec Json.143;
+    let Json.149 : List U8 = StructAtIndex 0 Json.495;
+    inc Json.149;
+    dec Json.495;
+    let Json.494 : I64 = 93i64;
+    let Json.493 : U8 = CallByName Num.127 Json.494;
+    let Json.490 : List U8 = CallByName List.4 Json.149 Json.493;
+    let Json.492 : I64 = 125i64;
+    let Json.491 : U8 = CallByName Num.127 Json.492;
+    let Json.489 : List U8 = CallByName List.4 Json.490 Json.491;
+    ret Json.489;
 
-procedure Json.130 (Json.430, Json.136):
-    let Json.134 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.134;
-    let Json.135 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.449 : {} = Struct {};
-    let Json.137 : List U8 = CallByName Encode.23 Json.134 Json.136 Json.449;
-    joinpoint Json.444 Json.138:
-        let Json.442 : U64 = 1i64;
-        let Json.441 : U64 = CallByName Num.20 Json.135 Json.442;
-        let Json.440 : {List U8, U64} = Struct {Json.138, Json.441};
-        ret Json.440;
+procedure Json.144 (Json.145, Json.486, #Attr.12):
+    let Json.143 : List [] = StructAtIndex 1 #Attr.12;
+    inc Json.143;
+    let Json.142 : Str = StructAtIndex 0 #Attr.12;
+    inc Json.142;
+    dec #Attr.12;
+    let Json.574 : I64 = 123i64;
+    let Json.573 : U8 = CallByName Num.127 Json.574;
+    let Json.570 : List U8 = CallByName List.4 Json.145 Json.573;
+    let Json.572 : I64 = 34i64;
+    let Json.571 : U8 = CallByName Num.127 Json.572;
+    let Json.568 : List U8 = CallByName List.4 Json.570 Json.571;
+    let Json.569 : List U8 = CallByName Str.12 Json.142;
+    let Json.565 : List U8 = CallByName List.8 Json.568 Json.569;
+    let Json.567 : I64 = 34i64;
+    let Json.566 : U8 = CallByName Num.127 Json.567;
+    let Json.562 : List U8 = CallByName List.4 Json.565 Json.566;
+    let Json.564 : I64 = 58i64;
+    let Json.563 : U8 = CallByName Num.127 Json.564;
+    let Json.559 : List U8 = CallByName List.4 Json.562 Json.563;
+    let Json.561 : I64 = 91i64;
+    let Json.560 : U8 = CallByName Num.127 Json.561;
+    let Json.147 : List U8 = CallByName List.4 Json.559 Json.560;
+    let Json.558 : U64 = CallByName List.6 Json.143;
+    let Json.546 : {List U8, U64} = Struct {Json.147, Json.558};
+    let Json.547 : {} = Struct {};
+    let Json.545 : {List U8, U64} = CallByName List.18 Json.143 Json.546 Json.547;
+    dec Json.143;
+    let Json.149 : List U8 = StructAtIndex 0 Json.545;
+    inc Json.149;
+    dec Json.545;
+    let Json.544 : I64 = 93i64;
+    let Json.543 : U8 = CallByName Num.127 Json.544;
+    let Json.540 : List U8 = CallByName List.4 Json.149 Json.543;
+    let Json.542 : I64 = 125i64;
+    let Json.541 : U8 = CallByName Num.127 Json.542;
+    let Json.539 : List U8 = CallByName List.4 Json.540 Json.541;
+    ret Json.539;
+
+procedure Json.146 (Json.488, Json.152):
+    let Json.150 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.150;
+    let Json.151 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.507 : {} = Struct {};
+    let Json.153 : List U8 = CallByName Encode.24 Json.150 Json.152 Json.507;
+    joinpoint Json.502 Json.154:
+        let Json.500 : U64 = 1i64;
+        let Json.499 : U64 = CallByName Num.20 Json.151 Json.500;
+        let Json.498 : {List U8, U64} = Struct {Json.154, Json.499};
+        ret Json.498;
     in
-    let Json.448 : U64 = 1i64;
-    let Json.445 : Int1 = CallByName Num.24 Json.135 Json.448;
-    if Json.445 then
-        let Json.447 : I64 = 44i64;
-        let Json.446 : U8 = CallByName Num.127 Json.447;
-        let Json.443 : List U8 = CallByName List.4 Json.137 Json.446;
-        jump Json.444 Json.443;
+    let Json.506 : U64 = 1i64;
+    let Json.503 : Int1 = CallByName Num.24 Json.151 Json.506;
+    if Json.503 then
+        let Json.505 : I64 = 44i64;
+        let Json.504 : U8 = CallByName Num.127 Json.505;
+        let Json.501 : List U8 = CallByName List.4 Json.153 Json.504;
+        jump Json.502 Json.501;
     else
-        jump Json.444 Json.137;
+        jump Json.502 Json.153;
 
-procedure Json.130 (Json.430, Json.136):
-    let Json.134 : List U8 = StructAtIndex 0 Json.430;
-    inc Json.134;
-    let Json.135 : U64 = StructAtIndex 1 Json.430;
-    dec Json.430;
-    let Json.499 : {} = Struct {};
-    let Json.137 : List U8 = CallByName Encode.23 Json.134 Json.136 Json.499;
-    dec Json.134;
-    joinpoint Json.494 Json.138:
-        let Json.492 : U64 = 1i64;
-        let Json.491 : U64 = CallByName Num.20 Json.135 Json.492;
-        let Json.490 : {List U8, U64} = Struct {Json.138, Json.491};
-        ret Json.490;
+procedure Json.146 (Json.488, Json.152):
+    let Json.150 : List U8 = StructAtIndex 0 Json.488;
+    inc Json.150;
+    let Json.151 : U64 = StructAtIndex 1 Json.488;
+    dec Json.488;
+    let Json.557 : {} = Struct {};
+    let Json.153 : List U8 = CallByName Encode.24 Json.150 Json.152 Json.557;
+    dec Json.150;
+    joinpoint Json.552 Json.154:
+        let Json.550 : U64 = 1i64;
+        let Json.549 : U64 = CallByName Num.20 Json.151 Json.550;
+        let Json.548 : {List U8, U64} = Struct {Json.154, Json.549};
+        ret Json.548;
     in
-    let Json.498 : U64 = 1i64;
-    let Json.495 : Int1 = CallByName Num.24 Json.135 Json.498;
-    if Json.495 then
-        let Json.497 : I64 = 44i64;
-        let Json.496 : U8 = CallByName Num.127 Json.497;
-        let Json.493 : List U8 = CallByName List.4 Json.137 Json.496;
-        jump Json.494 Json.493;
+    let Json.556 : U64 = 1i64;
+    let Json.553 : Int1 = CallByName Num.24 Json.151 Json.556;
+    if Json.553 then
+        let Json.555 : I64 = 44i64;
+        let Json.554 : U8 = CallByName Num.127 Json.555;
+        let Json.551 : List U8 = CallByName List.4 Json.153 Json.554;
+        jump Json.552 Json.551;
     else
-        jump Json.494 Json.137;
+        jump Json.552 Json.153;
 
-procedure Json.21 (Json.126, Json.127):
-    let Json.468 : {Str, List [C {}, C {}]} = Struct {Json.126, Json.127};
-    let Json.467 : {Str, List [C {}, C {}]} = CallByName Encode.22 Json.468;
-    ret Json.467;
+procedure Json.22 (Json.142, Json.143):
+    let Json.526 : {Str, List [C {}, C {}]} = Struct {Json.142, Json.143};
+    let Json.525 : {Str, List [C {}, C {}]} = CallByName Encode.23 Json.526;
+    ret Json.525;
 
-procedure Json.21 (Json.126, Json.127):
-    let Json.518 : {Str, List []} = Struct {Json.126, Json.127};
-    let Json.517 : {Str, List []} = CallByName Encode.22 Json.518;
-    ret Json.517;
+procedure Json.22 (Json.142, Json.143):
+    let Json.576 : {Str, List []} = Struct {Json.142, Json.143};
+    let Json.575 : {Str, List []} = CallByName Encode.23 Json.576;
+    ret Json.575;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.539 : {List U8, U64} = CallByName Json.130 List.140 List.141;
+    let List.539 : {List U8, U64} = CallByName Json.146 List.140 List.141;
     ret List.539;
 
 procedure List.139 (List.140, List.141, List.138):
-    let List.612 : {List U8, U64} = CallByName Json.130 List.140 List.141;
+    let List.612 : {List U8, U64} = CallByName Json.146 List.140 List.141;
     ret List.612;
 
 procedure List.18 (List.136, List.137, List.138):
@@ -334,7 +334,7 @@ procedure Str.12 (#Attr.2):
     ret Str.268;
 
 procedure Test.2 (Test.11):
-    let Test.18 : {{}, {}} = CallByName Encode.22 Test.11;
+    let Test.18 : {{}, {}} = CallByName Encode.23 Test.11;
     ret Test.18;
 
 procedure Test.3 ():
@@ -345,7 +345,7 @@ procedure Test.3 ():
 
 procedure Test.5 (Test.6, Test.7, Test.4):
     joinpoint Test.23 Test.8:
-        let Test.21 : List U8 = CallByName Encode.23 Test.6 Test.8 Test.7;
+        let Test.21 : List U8 = CallByName Encode.24 Test.6 Test.8 Test.7;
         ret Test.21;
     in
     let Test.28 : Int1 = CallByName Bool.2;
@@ -354,18 +354,18 @@ procedure Test.5 (Test.6, Test.7, Test.4):
         let Test.32 : {} = StructAtIndex 0 Test.4;
         let Test.31 : [C {}, C {}] = CallByName #Derived.0 Test.32;
         let Test.30 : List [C {}, C {}] = Array [Test.31];
-        let Test.22 : {Str, List [C {}, C {}]} = CallByName Json.21 Test.29 Test.30;
+        let Test.22 : {Str, List [C {}, C {}]} = CallByName Json.22 Test.29 Test.30;
         jump Test.23 Test.22;
     else
         let Test.24 : Str = "B";
         let Test.27 : {} = StructAtIndex 1 Test.4;
         let Test.26 : [C {}, C {}] = CallByName #Derived.5 Test.27;
         let Test.25 : List [C {}, C {}] = Array [Test.26];
-        let Test.22 : {Str, List [C {}, C {}]} = CallByName Json.21 Test.24 Test.25;
+        let Test.22 : {Str, List [C {}, C {}]} = CallByName Json.22 Test.24 Test.25;
         jump Test.23 Test.22;
 
 procedure Test.0 ():
     let Test.13 : {{}, {}} = CallByName Test.3;
     let Test.14 : {} = CallByName Json.1;
-    let Test.12 : List U8 = CallByName Encode.25 Test.13 Test.14;
+    let Test.12 : List U8 = CallByName Encode.26 Test.13 Test.14;
     ret Test.12;

crates/compiler/types/src/subs.rs

@@ -4459,6 +4459,7 @@ pub struct StorageSubs {
 struct StorageSubsOffsets {
     utable: u32,
     variables: u32,
+    tuple_elem_indices: u32,
     tag_names: u32,
     symbol_names: u32,
     field_names: u32,
@@ -4542,6 +4543,7 @@ impl StorageSubs {
         let self_offsets = StorageSubsOffsets {
             utable: self.subs.utable.len() as u32,
             variables: self.subs.variables.len() as u32,
+            tuple_elem_indices: self.subs.tuple_elem_indices.len() as u32,
             tag_names: self.subs.tag_names.len() as u32,
             symbol_names: self.subs.symbol_names.len() as u32,
             field_names: self.subs.field_names.len() as u32,
@@ -4553,6 +4555,7 @@ impl StorageSubs {
         let offsets = StorageSubsOffsets {
             utable: (target.utable.len() - Variable::NUM_RESERVED_VARS) as u32,
             variables: target.variables.len() as u32,
+            tuple_elem_indices: target.tuple_elem_indices.len() as u32,
             tag_names: target.tag_names.len() as u32,
             symbol_names: target.symbol_names.len() as u32,
             field_names: target.field_names.len() as u32,
@@ -4593,6 +4596,10 @@ impl StorageSubs {
                 .map(|v| Self::offset_variable(&offsets, *v)),
         );
 
+        target
+            .tuple_elem_indices
+            .extend(self.subs.tuple_elem_indices);
+
         target.variable_slices.extend(
             self.subs
                 .variable_slices
@@ -4613,6 +4620,11 @@ impl StorageSubs {
             (self_offsets.utable + offsets.utable) as usize
         );
 
+        debug_assert_eq!(
+            target.tuple_elem_indices.len(),
+            (self_offsets.tuple_elem_indices + offsets.tuple_elem_indices) as usize
+        );
+
         debug_assert_eq!(
             target.tag_names.len(),
             (self_offsets.tag_names + offsets.tag_names) as usize
@@ -4756,6 +4768,7 @@ impl StorageSubs {
     }
 
     fn offset_tuple_elems(offsets: &StorageSubsOffsets, mut tuple_elems: TupleElems) -> TupleElems {
+        tuple_elems.elem_index_start += offsets.tuple_elem_indices;
         tuple_elems.variables_start += offsets.variables;
 
         tuple_elems