Treat untyped suffixed functions as effectful

crates/cli/tests/cli_run.rs

@@ -986,6 +986,27 @@ mod cli_run {
         );
     }
 
+    #[test]
+    #[cfg_attr(windows, ignore)]
+    fn effectful_untyped_passed_fx() {
+        test_roc_app(
+            "crates/cli/tests/effectful",
+            "untyped_passed_fx.roc",
+            &[],
+            &[],
+            &[],
+            indoc!(
+                r#"
+                Before hello
+                Hello, World!
+                After hello
+                "#
+            ),
+            UseValgrind::No,
+            TestCliCommands::Dev,
+        );
+    }
+
     #[test]
     #[cfg_attr(windows, ignore)]
     fn transitive_expects() {

crates/cli/tests/effectful/untyped_passed_fx.roc

@@ -0,0 +1,13 @@
+app [main!] { pf: platform "../../../../examples/cli/effects-platform/main.roc" }
+
+import pf.Effect
+
+main! : {} => {}
+main! = \{} ->
+    logged! "hello" (\{} -> Effect.putLine! "Hello, World!")
+
+
+logged! = \name, fx! ->
+    Effect.putLine! "Before $(name)"
+    fx! {}
+    Effect.putLine! "After $(name)"

crates/compiler/can/src/copy.rs

@@ -984,7 +984,7 @@ fn deep_copy_type_vars<C: CopyEnv>(
 
             // Everything else is a mechanical descent.
             Structure(flat_type) => match flat_type {
-                EmptyRecord | EmptyTagUnion => Structure(flat_type),
+                EmptyRecord | EmptyTagUnion | EffectfulFunc => Structure(flat_type),
                 Apply(symbol, arguments) => {
                     descend_slice!(arguments);
 

crates/compiler/can/src/exhaustive.rs

@@ -153,6 +153,7 @@ fn index_var(
             }
             Content::Structure(structure) => match structure {
                 FlatType::Func(_, _, _, _) => return Err(TypeError),
+                FlatType::EffectfulFunc => return Err(TypeError),
                 FlatType::Apply(Symbol::LIST_LIST, args) => {
                     match (subs.get_subs_slice(*args), ctor) {
                         ([elem_var], IndexCtor::List) => {

crates/compiler/checkmate/schema.json

@@ -514,6 +514,20 @@
             }
           }
         },
+        {
+          "type": "object",
+          "required": [
+            "type"
+          ],
+          "properties": {
+            "type": {
+              "type": "string",
+              "enum": [
+                "EffectfulFunc"
+              ]
+            }
+          }
+        },
         {
           "type": "object",
           "required": [

crates/compiler/checkmate/src/convert.rs

@@ -127,6 +127,7 @@ impl AsSchema<Content> for subs::FlatType {
             ),
             subs::FlatType::EmptyRecord => Content::EmptyRecord(),
             subs::FlatType::EmptyTagUnion => Content::EmptyTagUnion(),
+            subs::FlatType::EffectfulFunc => Content::EffectfulFunc(),
         }
     }
 }

crates/compiler/checkmate_schema/src/lib.rs

@@ -99,6 +99,7 @@ impl_content! {
     },
     EmptyRecord {},
     EmptyTagUnion {},
+    EffectfulFunc {},
     RangedNumber {
         range: NumericRange,
     },

crates/compiler/constrain/src/pattern.rs

@@ -6,7 +6,7 @@ use roc_can::pattern::Pattern::{self, *};
 use roc_can::pattern::{DestructType, ListPatterns, RecordDestruct, TupleDestruct};
 use roc_collections::all::{HumanIndex, SendMap};
 use roc_collections::VecMap;
-use roc_module::ident::Lowercase;
+use roc_module::ident::{IdentSuffix, Lowercase};
 use roc_module::symbol::Symbol;
 use roc_region::all::{Loc, Region};
 use roc_types::subs::Variable;
@@ -299,12 +299,25 @@ pub fn constrain_pattern_help(
                     .push(constraints.is_open_type(type_index));
             }
 
+            // Identifiers introduced in nested patterns get let constraints
+            // and therefore don't need fx_pattern_suffix constraints.
             if is_shallow {
-                // Identifiers introduced in nested patterns get let constraints
+                match symbol.suffix() {
-                // and therefore don't need fx_pattern_suffix constraints.
+                    IdentSuffix::None => {
-                state
+                        // Unsuffixed identifiers should be constrained after we know if they're functions
-                    .delayed_fx_suffix_constraints
+                        state
-                    .push(constraints.fx_pattern_suffix(*symbol, type_index, region));
+                            .delayed_fx_suffix_constraints
+                            .push(constraints.fx_pattern_suffix(*symbol, type_index, region));
+                    }
+                    IdentSuffix::Bang => {
+                        // Bang suffixed identifiers are always required to be functions
+                        // We constrain this before the function's body,
+                        // so that we don't think it's pure and complain about leftover statements
+                        state
+                            .constraints
+                            .push(constraints.fx_pattern_suffix(*symbol, type_index, region));
+                    }
+                }
             }
 
             state.headers.insert(

crates/compiler/derive_key/src/decoding.rs

@@ -81,7 +81,7 @@ impl FlatDecodable {
                     Err(Underivable) // yet
                 }
                 //
-                FlatType::Func(..) => Err(Underivable),
+                FlatType::Func(..) | FlatType::EffectfulFunc => Err(Underivable),
             },
             Content::Alias(sym, _, real_var, _) => match from_builtin_symbol(sym) {
                 Some(lambda) => lambda,

crates/compiler/derive_key/src/encoding.rs

@@ -117,7 +117,7 @@ impl FlatEncodable {
                 }
                 FlatType::EmptyRecord => Ok(Key(FlatEncodableKey::Record(vec![]))),
                 FlatType::EmptyTagUnion => Ok(Key(FlatEncodableKey::TagUnion(vec![]))),
-                FlatType::Func(..) => Err(Underivable),
+                FlatType::Func(..) | FlatType::EffectfulFunc => Err(Underivable),
             },
             Content::Alias(sym, _, real_var, _) => match from_builtin_symbol(sym) {
                 Some(lambda) => lambda,

crates/compiler/derive_key/src/hash.rs

@@ -112,7 +112,7 @@ impl FlatHash {
                 FlatType::EmptyRecord => Ok(Key(FlatHashKey::Record(vec![]))),
                 FlatType::EmptyTagUnion => Ok(Key(FlatHashKey::TagUnion(vec![]))),
                 //
-                FlatType::Func(..) => Err(Underivable),
+                FlatType::Func(..) | FlatType::EffectfulFunc => Err(Underivable),
             },
             Content::Alias(sym, _, real_var, _) => match builtin_symbol_to_hash_lambda(sym) {
                 Some(lambda) => Ok(lambda),

crates/compiler/derive_key/src/inspect.rs

@@ -129,6 +129,9 @@ impl FlatInspectable {
                 FlatType::EmptyRecord => Key(FlatInspectableKey::Record(Vec::new())),
                 FlatType::EmptyTagUnion => Key(FlatInspectableKey::TagUnion(Vec::new())),
                 FlatType::Func(..) => Immediate(Symbol::INSPECT_FUNCTION),
+                FlatType::EffectfulFunc => {
+                    unreachable!("There must have been a bug in the solver, because we're trying to derive Inspect on a non-concrete type.");
+                }
             },
             Content::Alias(sym, _, real_var, kind) => match Self::from_builtin_alias(sym) {
                 Some(lambda) => lambda,

crates/compiler/lower_params/src/type_error.rs

@@ -210,6 +210,7 @@ fn drop_last_argument(err_type: &mut ErrorType) {
         | ErrorType::RecursiveTagUnion(_, _, _, _)
         | ErrorType::Alias(_, _, _, _)
         | ErrorType::Range(_)
-        | ErrorType::Error => {}
+        | ErrorType::Error
+        | ErrorType::EffectfulFunc => {}
     }
 }

crates/compiler/mono/src/ir.rs

@@ -10180,6 +10180,7 @@ fn find_lambda_sets_help(
                 }
                 FlatType::EmptyRecord => {}
                 FlatType::EmptyTagUnion => {}
+                FlatType::EffectfulFunc => {}
             },
             Content::Alias(_, _, actual, _) => {
                 stack.push(*actual);

crates/compiler/mono/src/layout.rs

@@ -2192,6 +2192,7 @@ fn lambda_set_size(subs: &Subs, var: Variable) -> (usize, usize, usize) {
                     }
                     stack.push((ext.var(), depth_any + 1, depth_lset));
                 }
+                FlatType::EffectfulFunc => internal_error!(),
                 FlatType::EmptyRecord | FlatType::EmptyTagUnion => {}
             },
             Content::FlexVar(_)
@@ -3465,6 +3466,7 @@ fn layout_from_flat_type<'a>(
         }
         EmptyTagUnion => cacheable(Ok(Layout::VOID)),
         EmptyRecord => cacheable(Ok(Layout::UNIT)),
+        EffectfulFunc => internal_error!(),
     }
 }
 

crates/compiler/solve/src/ability.rs

@@ -780,6 +780,12 @@ trait DerivableVisitor {
                     }
                     EmptyRecord => Self::visit_empty_record(var)?,
                     EmptyTagUnion => Self::visit_empty_tag_union(var)?,
+                    EffectfulFunc => {
+                        return Err(NotDerivable {
+                            var,
+                            context: NotDerivableContext::NoContext,
+                        })
+                    }
                 },
                 Alias(
                     Symbol::NUM_NUM | Symbol::NUM_INTEGER,

crates/compiler/solve/src/deep_copy.rs

@@ -187,7 +187,7 @@ fn deep_copy_var_help(
                         Func(new_arguments, new_closure_var, new_ret_var, new_fx_var)
                     }
 
-                    same @ EmptyRecord | same @ EmptyTagUnion => same,
+                    same @ (EmptyRecord | EmptyTagUnion | EffectfulFunc) => same,
 
                     Record(fields, ext_var) => {
                         let record_fields = {

crates/compiler/solve/src/solve.rs

@@ -1660,7 +1660,8 @@ fn solve_suffix_fx(
                 }
             }
             Content::FlexVar(_) => {
-                // [purity-inference] TODO: Require effectful fn
+                env.subs
+                    .set_content(variable, Content::Structure(FlatType::EffectfulFunc));
             }
             _ => {}
         },
@@ -2379,6 +2380,8 @@ fn adjust_rank_content(
                 // THEORY: an empty tag never needs to get generalized
                 EmptyTagUnion => Rank::toplevel(),
 
+                EffectfulFunc => Rank::toplevel(),
+
                 Record(fields, ext_var) => {
                     let mut rank = adjust_rank(subs, young_mark, visit_mark, group_rank, *ext_var);
 

crates/compiler/types/src/pretty_print.rs

@@ -15,6 +15,7 @@ use roc_module::symbol::{Interns, ModuleId, Symbol};
 pub static WILDCARD: &str = "*";
 static EMPTY_RECORD: &str = "{}";
 static EMPTY_TAG_UNION: &str = "[]";
+static EFFECTFUL_FUNC: &str = "! : ... => ?";
 
 /// Requirements for parentheses.
 ///
@@ -217,6 +218,7 @@ fn find_names_needed(
                 find_under_alias,
             );
         }
+        Structure(EffectfulFunc) => {}
         Structure(Record(sorted_fields, ext_var)) => {
             for index in sorted_fields.iter_variables() {
                 let var = subs[index];
@@ -1139,6 +1141,7 @@ fn write_flat_type<'a>(
             parens,
             pol,
         ),
+        EffectfulFunc => buf.push_str(EFFECTFUL_FUNC),
         Record(fields, ext_var) => {
             use crate::types::{gather_fields, RecordStructure};
 

crates/compiler/types/src/subs.rs

@@ -833,6 +833,7 @@ fn subs_fmt_flat_type(this: &FlatType, subs: &Subs, f: &mut fmt::Formatter) -> f
         }
         FlatType::EmptyRecord => write!(f, "EmptyRecord"),
         FlatType::EmptyTagUnion => write!(f, "EmptyTagUnion"),
+        FlatType::EffectfulFunc => write!(f, "EffectfulFunc"),
     }
 }
 
@@ -2584,6 +2585,8 @@ impl TagExt {
 pub enum FlatType {
     Apply(Symbol, VariableSubsSlice),
     Func(VariableSubsSlice, Variable, Variable, Variable),
+    /// A function that we know nothing about yet except that it's effectful
+    EffectfulFunc,
     Record(RecordFields, Variable),
     Tuple(TupleElems, Variable),
     TagUnion(UnionTags, TagExt),
@@ -3492,7 +3495,7 @@ fn occurs(
 
                     short_circuit_help(subs, root_var, ctx, ext_var)
                 }
-                EmptyRecord | EmptyTagUnion => Ok(()),
+                EmptyRecord | EmptyTagUnion | EffectfulFunc => Ok(()),
             },
             Alias(_, args, _, _) => {
                 // THEORY: we only need to explore the args, as that is the surface of all
@@ -3686,7 +3689,7 @@ fn explicit_substitute(
                         subs.set_content(in_var, Structure(Tuple(vars_by_elem, new_ext)));
                     }
 
-                    EmptyRecord | EmptyTagUnion => {}
+                    EmptyRecord | EmptyTagUnion | EffectfulFunc => {}
                 }
 
                 in_var
@@ -3872,7 +3875,9 @@ fn get_var_names(
                     accum
                 }
 
-                FlatType::EmptyRecord | FlatType::EmptyTagUnion => taken_names,
+                FlatType::EmptyRecord | FlatType::EmptyTagUnion | FlatType::EffectfulFunc => {
+                    taken_names
+                }
 
                 FlatType::Record(vars_by_field, ext) => {
                     let mut accum = get_var_names(subs, ext, taken_names);
@@ -4236,6 +4241,7 @@ fn flat_type_to_err_type(
             ErrorType::Function(args, Box::new(closure), fx, Box::new(ret))
         }
 
+        EffectfulFunc => ErrorType::EffectfulFunc,
         EmptyRecord => ErrorType::Record(SendMap::default(), TypeExt::Closed),
         EmptyTagUnion => ErrorType::TagUnion(SendMap::default(), TypeExt::Closed, pol),
 
@@ -4694,6 +4700,7 @@ impl StorageSubs {
             ),
             FlatType::EmptyRecord => FlatType::EmptyRecord,
             FlatType::EmptyTagUnion => FlatType::EmptyTagUnion,
+            FlatType::EffectfulFunc => FlatType::EffectfulFunc,
         }
     }
 
@@ -5084,6 +5091,8 @@ fn storage_copy_var_to_help(env: &mut StorageCopyVarToEnv<'_>, var: Variable) ->
 
                     RecursiveTagUnion(new_rec_var, union_tags, new_ext)
                 }
+
+                EffectfulFunc => EffectfulFunc,
             };
 
             env.target
@@ -5552,6 +5561,7 @@ fn copy_import_to_help(env: &mut CopyImportEnv<'_>, max_rank: Rank, var: Variabl
 
                     RecursiveTagUnion(new_rec_var, union_tags, new_ext)
                 }
+                EffectfulFunc => EffectfulFunc,
             };
 
             env.target
@@ -5890,6 +5900,8 @@ fn instantiate_rigids_help(subs: &mut Subs, max_rank: Rank, initial: Variable) {
                     stack.push(ext.var());
                     stack.push(rec_var);
                 }
+
+                EffectfulFunc => {}
             },
             Alias(_, args, var, _) => {
                 let var = *var;
@@ -5997,7 +6009,7 @@ pub fn get_member_lambda_sets_at_region(subs: &Subs, var: Variable, target_regio
                     );
                     stack.push(ext.var());
                 }
-                FlatType::EmptyRecord | FlatType::EmptyTagUnion => {}
+                FlatType::EffectfulFunc | FlatType::EmptyRecord | FlatType::EmptyTagUnion => {}
             },
             Content::Alias(_, _, real_var, _) => {
                 stack.push(*real_var);
@@ -6073,6 +6085,7 @@ fn is_inhabited(subs: &Subs, var: Variable) -> bool {
                         return false;
                     }
                 }
+                FlatType::EffectfulFunc => {}
                 FlatType::FunctionOrTagUnion(_, _, _) => {}
                 FlatType::EmptyRecord => {}
                 FlatType::EmptyTagUnion => {

crates/compiler/types/src/types.rs

@@ -3660,6 +3660,7 @@ pub enum ErrorType {
     /// If the name was auto-generated, it will start with a `#`.
     FlexVar(Lowercase),
     RigidVar(Lowercase),
+    EffectfulFunc,
     /// If the name was auto-generated, it will start with a `#`.
     FlexAbleVar(Lowercase, AbilitySet),
     RigidAbleVar(Lowercase, AbilitySet),
@@ -3750,6 +3751,7 @@ impl ErrorType {
                     t.add_names(taken);
                 });
             }
+            EffectfulFunc => {}
             Error => {}
         }
     }
@@ -3902,6 +3904,7 @@ fn write_debug_error_type_help(error_type: ErrorType, buf: &mut String, parens:
                 buf.push(')');
             }
         }
+        EffectfulFunc => buf.push_str("EffectfulFunc"),
         Type(symbol, arguments) => {
             let write_parens = parens == Parens::InTypeParam && !arguments.is_empty();
 

crates/compiler/unify/src/unify.rs

@@ -3334,6 +3334,17 @@ fn unify_flat_type<M: MetaCollector>(
 
             outcome
         }
+        (EffectfulFunc, Func(args, closure, ret, fx)) => {
+            let mut outcome = unify_pool(env, pool, Variable::EFFECTFUL, *fx, ctx.mode);
+
+            outcome.union(merge(
+                env,
+                ctx,
+                Structure(Func(*args, *closure, *ret, Variable::EFFECTFUL)),
+            ));
+
+            outcome
+        }
         (FunctionOrTagUnion(tag_names, tag_symbols, ext), Func(args, closure, ret, fx)) => {
             unify_function_or_tag_union_and_func(
                 env,

crates/glue/src/load.rs

@@ -10,7 +10,7 @@ use roc_build::{
     },
 };
 use roc_collections::MutMap;
-use roc_error_macros::todo_lambda_erasure;
+use roc_error_macros::{internal_error, todo_lambda_erasure};
 use roc_gen_llvm::run_roc::RocCallResult;
 use roc_load::{ExecutionMode, FunctionKind, LoadConfig, LoadedModule, LoadingProblem, Threading};
 use roc_mono::ir::{generate_glue_procs, CrashTag, GlueProc, OptLevel};
@@ -324,6 +324,7 @@ fn number_lambda_sets(subs: &Subs, initial: Variable) -> Vec<Variable> {
 
                 EmptyRecord => (),
                 EmptyTagUnion => (),
+                EffectfulFunc => internal_error!(),
 
                 Record(fields, ext) => {
                     let fields = *fields;

crates/glue/src/types.rs

@@ -1340,7 +1340,8 @@ fn add_type_help<'a>(
         Content::FlexVar(_)
         | Content::RigidVar(_)
         | Content::FlexAbleVar(_, _)
-        | Content::RigidAbleVar(_, _) => {
+        | Content::RigidAbleVar(_, _)
+        | Content::Structure(FlatType::EffectfulFunc) => {
             todo!("TODO give a nice error message for a non-concrete type being passed to the host")
         }
         Content::Structure(FlatType::Tuple(..)) => {

crates/reporting/src/error/type.rs

@@ -2767,6 +2767,8 @@ fn to_doc_help<'b>(
             alloc.type_variable(lowercase)
         }
 
+        EffectfulFunc => alloc.text("effectful function"),
+
         Type(symbol, args) => report_text::apply(
             alloc,
             parens,
@@ -2961,6 +2963,7 @@ fn count_generated_name_usages<'a>(
             RigidVar(name) | RigidAbleVar(name, _) => {
                 debug_assert!(!is_generated_name(name));
             }
+            EffectfulFunc => {}
             Type(_, tys) => {
                 stack.extend(tys.iter().map(|t| (t, only_unseen)));
             }
@@ -3820,7 +3823,9 @@ fn should_show_diff(t1: &ErrorType, t2: &ErrorType) -> bool {
         | (RecursiveTagUnion(_, _, _, _), _)
         | (_, RecursiveTagUnion(_, _, _, _))
         | (Function(_, _, _, _), _)
-        | (_, Function(_, _, _, _)) => true,
+        | (_, Function(_, _, _, _))
+        | (EffectfulFunc, _)
+        | (_, EffectfulFunc) => true,
     }
 }
 
@@ -4861,7 +4866,7 @@ fn type_problem_to_pretty<'b>(
             };
 
             match tipe {
-                Infinite | Error | FlexVar(_) => alloc.nil(),
+                Infinite | Error | FlexVar(_) | EffectfulFunc => alloc.nil(),
                 FlexAbleVar(_, other_abilities) => {
                     rigid_able_vs_different_flex_able(x, abilities, other_abilities)
                 }
@@ -4954,6 +4959,7 @@ fn type_problem_to_pretty<'b>(
                     };
                     bad_rigid_var(x, msg)
                 }
+                EffectfulFunc => alloc.reflow("an effectful function"),
                 RigidVar(y) | RigidAbleVar(y, _) => bad_double_rigid(x, y),
                 Function(_, _, _, _) => bad_rigid_var(x, alloc.reflow("a function value")),
                 Record(_, _) => bad_rigid_var(x, alloc.reflow("a record value")),