diff --git a/compiler/builtins/docs/Defaults.roc b/compiler/builtins/docs/Defaults.roc
index 611ef249a1..046ba7dc3f 100644
--- a/compiler/builtins/docs/Defaults.roc
+++ b/compiler/builtins/docs/Defaults.roc
@@ -1,7 +1,7 @@
 interface Defaults
     exposes []
     imports [
-        Map.{ Map },
+        Dict.{ Dict },
         Set.{ Set },
         Num.{ Num, Int, Float }
     ]
diff --git a/compiler/builtins/docs/Map.roc b/compiler/builtins/docs/Dict.roc
similarity index 56%
rename from compiler/builtins/docs/Map.roc
rename to compiler/builtins/docs/Dict.roc
index 0a25daae4d..36056e81e5 100644
--- a/compiler/builtins/docs/Map.roc
+++ b/compiler/builtins/docs/Dict.roc
@@ -1,15 +1,15 @@
-interface Map2
+interface Dict2
     exposes [ isEmpty, map ]
     imports []
 
-isEmpty : Map * * -> Bool
+isEmpty : Dict * * -> Bool
 
-## Convert each key and value in the #Map to something new, by calling a conversion
+## Convert each key and value in the #Dict to something new, by calling a conversion
 ## function on each of them. Then return a new #Map of the converted keys and values.
 ## 
-## >>> Map.map {{ 3.14 => "pi", 1.0 => "one" }} \{ key, value } -> { key:
+## >>> Dict.map {{ 3.14 => "pi", 1.0 => "one" }} \{ key, value } -> { key:
 ## 
-## >>> Map.map {[ "", "a", "bc" ]} Str.isEmpty
+## >>> Dict.map {[ "", "a", "bc" ]} Str.isEmpty
 ## 
 ## `map` functions like this are common in Roc, and they all work similarly.
 ## See for example #Result.map, #List.map, and #Set.map.
diff --git a/compiler/builtins/src/std.rs b/compiler/builtins/src/std.rs
index 120e78dc58..97e8b2581a 100644
--- a/compiler/builtins/src/std.rs
+++ b/compiler/builtins/src/std.rs
@@ -3,7 +3,7 @@ use roc_module::ident::TagName;
 use roc_module::symbol::Symbol;
 use roc_region::all::Region;
 use roc_types::builtin_aliases::{
-    bool_type, float_type, int_type, list_type, map_type, num_type, ordering_type, result_type,
+    bool_type, dict_type, float_type, int_type, list_type, num_type, ordering_type, result_type,
     set_type, str_type,
 };
 use roc_types::solved_types::SolvedType;
@@ -30,7 +30,7 @@ pub fn standard_stdlib() -> StdLib {
         applies: vec![
             Symbol::LIST_LIST,
             Symbol::SET_SET,
-            Symbol::MAP_MAP,
+            Symbol::DICT_DICT,
             Symbol::STR_STR,
         ]
         .into_iter()
@@ -614,39 +614,43 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         top_level_function(vec![list_type(flex(TVAR1))], Box::new(bool_type())),
     );
 
-    // Map module
+    // Dict module
 
-    // empty : Map k v
-    add_type(Symbol::MAP_EMPTY, map_type(flex(TVAR1), flex(TVAR2)));
+    // empty : Dict k v
+    add_type(Symbol::DICT_EMPTY, dict_type(flex(TVAR1), flex(TVAR2)));
 
-    // singleton : k, v -> Map k v
+    // singleton : k, v -> Dict k v
     add_type(
-        Symbol::MAP_SINGLETON,
+        Symbol::DICT_SINGLETON,
         top_level_function(
             vec![flex(TVAR1), flex(TVAR2)],
-            Box::new(map_type(flex(TVAR1), flex(TVAR2))),
+            Box::new(dict_type(flex(TVAR1), flex(TVAR2))),
         ),
     );
 
-    // get : Map k v, k -> Result v [ KeyNotFound ]*
+    // get : Dict k v, k -> Result v [ KeyNotFound ]*
     let key_not_found = SolvedType::TagUnion(
         vec![(TagName::Global("KeyNotFound".into()), vec![])],
         Box::new(SolvedType::Wildcard),
     );
 
     add_type(
-        Symbol::MAP_GET,
+        Symbol::DICT_GET,
         top_level_function(
-            vec![map_type(flex(TVAR1), flex(TVAR2)), flex(TVAR1)],
+            vec![dict_type(flex(TVAR1), flex(TVAR2)), flex(TVAR1)],
             Box::new(result_type(flex(TVAR2), key_not_found)),
         ),
     );
 
     add_type(
-        Symbol::MAP_INSERT,
+        Symbol::DICT_INSERT,
         top_level_function(
-            vec![map_type(flex(TVAR1), flex(TVAR2)), flex(TVAR1), flex(TVAR2)],
-            Box::new(map_type(flex(TVAR1), flex(TVAR2))),
+            vec![
+                dict_type(flex(TVAR1), flex(TVAR2)),
+                flex(TVAR1),
+                flex(TVAR2),
+            ],
+            Box::new(dict_type(flex(TVAR1), flex(TVAR2))),
         ),
     );
 
diff --git a/compiler/builtins/src/unique.rs b/compiler/builtins/src/unique.rs
index 43cddc7461..b608f699b7 100644
--- a/compiler/builtins/src/unique.rs
+++ b/compiler/builtins/src/unique.rs
@@ -107,7 +107,7 @@ pub fn uniq_stdlib() -> StdLib {
             Symbol::ATTR_ATTR,
             Symbol::LIST_LIST,
             Symbol::SET_SET,
-            Symbol::MAP_MAP,
+            Symbol::DICT_DICT,
             Symbol::STR_STR,
         ]
         .into_iter()
@@ -831,18 +831,18 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         )
     });
 
-    // Map module
+    // Dict module
 
-    // empty : Attr * (Map k v)
-    add_type(Symbol::MAP_EMPTY, {
+    // empty : Attr * (Dict k v)
+    add_type(Symbol::DICT_EMPTY, {
         let_tvars! { star, k , v };
-        map_type(star, k, v)
+        dict_type(star, k, v)
     });
 
-    // singleton : k, v -> Attr * (Map k v)
-    add_type(Symbol::MAP_SINGLETON, {
+    // singleton : k, v -> Attr * (Dict k v)
+    add_type(Symbol::DICT_SINGLETON, {
         let_tvars! { star, k , v };
-        unique_function(vec![flex(k), flex(v)], map_type(star, k, v))
+        unique_function(vec![flex(k), flex(v)], dict_type(star, k, v))
     });
 
     let key_not_found = SolvedType::Apply(
@@ -856,10 +856,10 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         ],
     );
 
-    // get : Attr (* | u) (Map (Attr * key) (Attr u val))
+    // get : Attr (* | u) (Dict (Attr * key) (Attr u val))
     //     , Attr * key
     //    -> Attr * (Result (Attr u val) [ KeyNotFound ]*)
-    add_type(Symbol::MAP_GET, {
+    add_type(Symbol::DICT_GET, {
         let_tvars! { u, key, val, star1, star2, star3, star4 };
 
         unique_function(
@@ -869,7 +869,7 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
                     vec![
                         container(star1, vec![u]),
                         SolvedType::Apply(
-                            Symbol::MAP_MAP,
+                            Symbol::DICT_DICT,
                             vec![attr_type(star2, key), attr_type(u, val)],
                         ),
                     ],
@@ -889,11 +889,11 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         )
     });
 
-    // insert : Attr * (Map key value)
+    // insert : Attr * (Dict key value)
     //        , key
     //        , value
-    //        , Attr * (Map key value)
-    add_type(Symbol::MAP_INSERT, {
+    //        , Attr * (Dict key value)
+    add_type(Symbol::DICT_INSERT, {
         let_tvars! { star1, star2, key, value };
 
         unique_function(
@@ -902,7 +902,7 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
                     Symbol::ATTR_ATTR,
                     vec![
                         flex(star1),
-                        SolvedType::Apply(Symbol::MAP_MAP, vec![flex(key), flex(value)]),
+                        SolvedType::Apply(Symbol::DICT_DICT, vec![flex(key), flex(value)]),
                     ],
                 ),
                 flex(key),
@@ -912,7 +912,7 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
                 Symbol::ATTR_ATTR,
                 vec![
                     flex(star2),
-                    SolvedType::Apply(Symbol::MAP_MAP, vec![flex(key), flex(value)]),
+                    SolvedType::Apply(Symbol::DICT_DICT, vec![flex(key), flex(value)]),
                 ],
             ),
         )
@@ -1267,12 +1267,12 @@ fn set_type(u: VarId, a: VarId) -> SolvedType {
 }
 
 #[inline(always)]
-fn map_type(u: VarId, key: VarId, value: VarId) -> SolvedType {
+fn dict_type(u: VarId, key: VarId, value: VarId) -> SolvedType {
     SolvedType::Apply(
         Symbol::ATTR_ATTR,
         vec![
             flex(u),
-            SolvedType::Apply(Symbol::MAP_MAP, vec![flex(key), flex(value)]),
+            SolvedType::Apply(Symbol::DICT_DICT, vec![flex(key), flex(value)]),
         ],
     )
 }
diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index a32b2a1bc3..335eb91c1e 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -477,17 +477,16 @@ pub fn build_exp_literal<'a, 'ctx, 'env>(
             } else {
                 let ctx = env.context;
                 let builder = env.builder;
-                let len_u64 = str_literal.len() as u64;
-                let elem_bytes = CHAR_LAYOUT.stack_size(env.ptr_bytes) as u64;
+                let number_of_chars = str_literal.len() as u64;
                 let ptr_bytes = env.ptr_bytes;
 
                 let populate_str = |ptr| {
                     // Copy the elements from the list literal into the array
-                    for (index, char) in str_literal.as_bytes().iter().enumerate() {
+                    for (index, character) in str_literal.as_bytes().iter().enumerate() {
                         let val = env
                             .context
                             .i8_type()
-                            .const_int(*char as u64, false)
+                            .const_int(*character as u64, false)
                             .as_basic_value_enum();
                         let index_val = ctx.i64_type().const_int(index as u64, false);
                         let elem_ptr =
@@ -554,14 +553,14 @@ pub fn build_exp_literal<'a, 'ctx, 'env>(
                         "small_str_array",
                     )
                 } else {
-                    let bytes_len = elem_bytes * len_u64;
-                    let len_type = env.ptr_int();
-                    let len = len_type.const_int(bytes_len, false);
+                    let number_of_elements = env.ptr_int().const_int(number_of_chars, false);
 
                     // NOTE we rely on CHAR_LAYOUT turning into a `i8`
-                    let ptr = allocate_list(env, InPlace::Clone, &CHAR_LAYOUT, len);
+                    let ptr = allocate_list(env, InPlace::Clone, &CHAR_LAYOUT, number_of_elements);
                     let struct_type = collection(ctx, ptr_bytes);
 
+                    populate_str(ptr);
+
                     let mut struct_val;
 
                     // Store the pointer
@@ -576,11 +575,14 @@ pub fn build_exp_literal<'a, 'ctx, 'env>(
 
                     // Store the length
                     struct_val = builder
-                        .build_insert_value(struct_val, len, Builtin::WRAPPER_LEN, "insert_len")
+                        .build_insert_value(
+                            struct_val,
+                            number_of_elements,
+                            Builtin::WRAPPER_LEN,
+                            "insert_len",
+                        )
                         .unwrap();
 
-                    populate_str(ptr);
-
                     builder.build_bitcast(
                         struct_val.into_struct_value(),
                         collection(ctx, ptr_bytes),
@@ -2170,15 +2172,24 @@ pub fn build_proc_header<'a, 'ctx, 'env>(
             for (name, layout) in aliases {
                 match layout {
                     Layout::Closure(arguments, closure, result) => {
+                        // define closure size and return value size, e.g.
+                        //
+                        // * roc__mainForHost_1_Update_size() -> i64
+                        // * roc__mainForHost_1_Update_result_size() -> i64
                         build_closure_caller(env, &fn_name, *name, arguments, closure, result)
                     }
-                    Layout::FunctionPointer(_arguments, _result) => {
-                        // TODO should this be considered a closure of size 0?
-                        // or do we let the host call it directly?
-                        // then we have no RocCallResult wrapping though
+                    Layout::FunctionPointer(arguments, result) => {
+                        // define function size (equal to pointer size) and return value size, e.g.
+                        //
+                        // * roc__mainForHost_1_Update_size() -> i64
+                        // * roc__mainForHost_1_Update_result_size() -> i64
+                        build_function_caller(env, &fn_name, *name, arguments, result)
                     }
                     _ => {
-                        // TODO
+                        // for anything else we only define the size symbol, e.g.
+                        //
+                        // * roc__mainForHost_1_Model_size() -> i64
+                        build_host_exposed_alias_size(env, &fn_name, *name, layout)
                     }
                 }
             }
@@ -2298,23 +2309,187 @@ pub fn build_closure_caller<'a, 'ctx, 'env>(
 
     let closure_data = builder.build_load(closure_data_ptr, "load_closure_data");
 
-    let mut arguments = parameters;
-    arguments.push(closure_data);
+    let mut parameters = parameters;
+    parameters.push(closure_data);
 
-    let result = invoke_and_catch(env, function_value, function_ptr, &arguments, result_type);
+    let call_result = invoke_and_catch(env, function_value, function_ptr, &parameters, result_type);
 
-    builder.build_store(output, result);
+    builder.build_store(output, call_result);
 
     builder.build_return(None);
 
     // STEP 3: build a {} -> u64 function that gives the size of the return type
-    let size_function_type = env.context.i64_type().fn_type(&[], false);
-    let size_function_name: String = format!(
-        "roc_{}_{}_size",
+    build_host_exposed_alias_size_help(
+        env,
+        def_name,
+        alias_symbol,
+        Some("result"),
+        roc_call_result_type.into(),
+    );
+
+    // STEP 4: build a {} -> u64 function that gives the size of the closure
+    let layout = Layout::Closure(arguments, closure.clone(), result);
+    build_host_exposed_alias_size(env, def_name, alias_symbol, &layout);
+}
+
+pub fn build_function_caller<'a, 'ctx, 'env>(
+    env: &'a Env<'a, 'ctx, 'env>,
+    def_name: &str,
+    alias_symbol: Symbol,
+    arguments: &[Layout<'a>],
+    result: &Layout<'a>,
+) {
+    use inkwell::types::BasicType;
+
+    let arena = env.arena;
+    let context = &env.context;
+    let builder = env.builder;
+
+    // STEP 1: build function header
+
+    // e.g. `roc__main_1_Fx_caller`
+    let function_name = format!(
+        "roc_{}_{}_caller",
         def_name,
         alias_symbol.ident_string(&env.interns)
     );
 
+    let mut argument_types = Vec::with_capacity_in(arguments.len() + 3, env.arena);
+
+    for layout in arguments {
+        argument_types.push(basic_type_from_layout(
+            arena,
+            context,
+            layout,
+            env.ptr_bytes,
+        ));
+    }
+
+    let function_pointer_type = {
+        let mut args = Vec::new_in(env.arena);
+        args.extend(arguments.iter().cloned());
+
+        // pretend the closure layout is empty
+        args.push(Layout::Struct(&[]));
+
+        let function_layout = Layout::FunctionPointer(&args, result);
+
+        // this is already a (function) pointer type
+        basic_type_from_layout(arena, context, &function_layout, env.ptr_bytes)
+    };
+    argument_types.push(function_pointer_type);
+
+    let closure_argument_type = {
+        let basic_type =
+            basic_type_from_layout(arena, context, &Layout::Struct(&[]), env.ptr_bytes);
+
+        basic_type.ptr_type(AddressSpace::Generic)
+    };
+    argument_types.push(closure_argument_type.into());
+
+    let result_type = basic_type_from_layout(arena, context, result, env.ptr_bytes);
+
+    let roc_call_result_type =
+        context.struct_type(&[context.i64_type().into(), result_type], false);
+
+    let output_type = { roc_call_result_type.ptr_type(AddressSpace::Generic) };
+    argument_types.push(output_type.into());
+
+    let function_type = context.void_type().fn_type(&argument_types, false);
+
+    let function_value = env.module.add_function(
+        function_name.as_str(),
+        function_type,
+        Some(Linkage::External),
+    );
+
+    function_value.set_call_conventions(C_CALL_CONV);
+
+    // STEP 2: build function body
+
+    let entry = context.append_basic_block(function_value, "entry");
+
+    builder.position_at_end(entry);
+
+    let mut parameters = function_value.get_params();
+    let output = parameters.pop().unwrap().into_pointer_value();
+    let _closure_data_ptr = parameters.pop().unwrap().into_pointer_value();
+    let function_ptr = parameters.pop().unwrap().into_pointer_value();
+
+    // let closure_data = context.struct_type(&[], false).const_zero().into();
+
+    let actual_function_type = basic_type_from_layout(
+        arena,
+        context,
+        &Layout::FunctionPointer(arguments, result),
+        env.ptr_bytes,
+    );
+
+    let function_ptr = builder
+        .build_bitcast(function_ptr, actual_function_type, "cast")
+        .into_pointer_value();
+
+    let call_result = invoke_and_catch(env, function_value, function_ptr, &parameters, result_type);
+
+    builder.build_store(output, call_result);
+
+    builder.build_return(None);
+
+    // STEP 3: build a {} -> u64 function that gives the size of the return type
+    build_host_exposed_alias_size_help(
+        env,
+        def_name,
+        alias_symbol,
+        Some("result"),
+        roc_call_result_type.into(),
+    );
+
+    // STEP 4: build a {} -> u64 function that gives the size of the function
+    let layout = Layout::FunctionPointer(arguments, result);
+    build_host_exposed_alias_size(env, def_name, alias_symbol, &layout);
+}
+
+fn build_host_exposed_alias_size<'a, 'ctx, 'env>(
+    env: &'a Env<'a, 'ctx, 'env>,
+    def_name: &str,
+    alias_symbol: Symbol,
+    layout: &Layout<'a>,
+) {
+    build_host_exposed_alias_size_help(
+        env,
+        def_name,
+        alias_symbol,
+        None,
+        basic_type_from_layout(env.arena, env.context, layout, env.ptr_bytes),
+    )
+}
+
+fn build_host_exposed_alias_size_help<'a, 'ctx, 'env>(
+    env: &'a Env<'a, 'ctx, 'env>,
+    def_name: &str,
+    alias_symbol: Symbol,
+    opt_label: Option<&str>,
+    basic_type: BasicTypeEnum<'ctx>,
+) {
+    let builder = env.builder;
+    let context = env.context;
+
+    let size_function_type = env.context.i64_type().fn_type(&[], false);
+    let size_function_name: String = if let Some(label) = opt_label {
+        format!(
+            "roc_{}_{}_{}_size",
+            def_name,
+            alias_symbol.ident_string(&env.interns),
+            label
+        )
+    } else {
+        format!(
+            "roc_{}_{}_size",
+            def_name,
+            alias_symbol.ident_string(&env.interns)
+        )
+    };
+
     let size_function = env.module.add_function(
         size_function_name.as_str(),
         size_function_type,
@@ -2325,7 +2500,8 @@ pub fn build_closure_caller<'a, 'ctx, 'env>(
 
     builder.position_at_end(entry);
 
-    let size: BasicValueEnum = roc_call_result_type.size_of().unwrap().into();
+    use inkwell::types::BasicType;
+    let size: BasicValueEnum = basic_type.size_of().unwrap().into();
     builder.build_return(Some(&size));
 }
 
diff --git a/compiler/gen/src/llvm/build_list.rs b/compiler/gen/src/llvm/build_list.rs
index 4049f38e05..6b7b3e99e1 100644
--- a/compiler/gen/src/llvm/build_list.rs
+++ b/compiler/gen/src/llvm/build_list.rs
@@ -2067,7 +2067,7 @@ pub fn allocate_list<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     inplace: InPlace,
     elem_layout: &Layout<'a>,
-    length: IntValue<'ctx>,
+    number_of_elements: IntValue<'ctx>,
 ) -> PointerValue<'ctx> {
     let builder = env.builder;
     let ctx = env.context;
@@ -2075,10 +2075,11 @@ pub fn allocate_list<'a, 'ctx, 'env>(
     let len_type = env.ptr_int();
     let elem_bytes = elem_layout.stack_size(env.ptr_bytes) as u64;
     let bytes_per_element = len_type.const_int(elem_bytes, false);
-    let number_of_data_bytes = builder.build_int_mul(bytes_per_element, length, "data_length");
+    let number_of_data_bytes =
+        builder.build_int_mul(bytes_per_element, number_of_elements, "data_length");
 
     let rc1 = match inplace {
-        InPlace::InPlace => length,
+        InPlace::InPlace => number_of_elements,
         InPlace::Clone => {
             // the refcount of a new list is initially 1
             // we assume that the list is indeed used (dead variables are eliminated)
diff --git a/compiler/gen/src/llvm/convert.rs b/compiler/gen/src/llvm/convert.rs
index cb7842b859..97d23fd622 100644
--- a/compiler/gen/src/llvm/convert.rs
+++ b/compiler/gen/src/llvm/convert.rs
@@ -158,7 +158,7 @@ pub fn basic_type_from_layout<'ctx>(
             Float64 => context.f64_type().as_basic_type_enum(),
             Float32 => context.f32_type().as_basic_type_enum(),
             Float16 => context.f16_type().as_basic_type_enum(),
-            Map(_, _) | EmptyMap => panic!("TODO layout_to_basic_type for Builtin::Map"),
+            Dict(_, _) | EmptyDict => panic!("TODO layout_to_basic_type for Builtin::Dict"),
             Set(_) | EmptySet => panic!("TODO layout_to_basic_type for Builtin::Set"),
             List(_, _) | Str | EmptyStr => collection(context, ptr_bytes).into(),
             EmptyList => BasicTypeEnum::StructType(collection(context, ptr_bytes)),
diff --git a/compiler/gen/src/llvm/refcounting.rs b/compiler/gen/src/llvm/refcounting.rs
index 0ef67b4960..8729439750 100644
--- a/compiler/gen/src/llvm/refcounting.rs
+++ b/compiler/gen/src/llvm/refcounting.rs
@@ -59,13 +59,10 @@ impl<'ctx> PointerToRefcount<'ctx> {
         let builder = env.builder;
         // pointer to usize
         let refcount_type = ptr_int(env.context, env.ptr_bytes);
+        let refcount_ptr_type = refcount_type.ptr_type(AddressSpace::Generic);
 
-        let ptr_as_usize_ptr = cast_basic_basic(
-            builder,
-            data_ptr.into(),
-            refcount_type.ptr_type(AddressSpace::Generic).into(),
-        )
-        .into_pointer_value();
+        let ptr_as_usize_ptr = cast_basic_basic(builder, data_ptr.into(), refcount_ptr_type.into())
+            .into_pointer_value();
 
         // get a pointer to index -1
         let index_intvalue = refcount_type.const_int((-1 as i64) as u64, false);
@@ -400,7 +397,7 @@ fn decrement_refcount_builtin<'a, 'ctx, 'env>(
             }
             todo!();
         }
-        Map(key_layout, value_layout) => {
+        Dict(key_layout, value_layout) => {
             if key_layout.contains_refcounted() || value_layout.contains_refcounted() {
                 // TODO decrement all values
             }
@@ -431,6 +428,24 @@ pub fn increment_refcount_layout<'a, 'ctx, 'env>(
         RecursiveUnion(tags) => {
             build_inc_union(env, layout_ids, tags, value);
         }
+        Closure(_, closure_layout, _) => {
+            if closure_layout.contains_refcounted() {
+                let wrapper_struct = value.into_struct_value();
+
+                let field_ptr = env
+                    .builder
+                    .build_extract_value(wrapper_struct, 1, "increment_closure_data")
+                    .unwrap();
+
+                increment_refcount_layout(
+                    env,
+                    parent,
+                    layout_ids,
+                    field_ptr,
+                    &closure_layout.as_block_of_memory_layout(),
+                )
+            }
+        }
         _ => {}
     }
 }
@@ -483,7 +498,7 @@ fn increment_refcount_builtin<'a, 'ctx, 'env>(
             }
             todo!();
         }
-        Map(key_layout, value_layout) => {
+        Dict(key_layout, value_layout) => {
             if key_layout.contains_refcounted() || value_layout.contains_refcounted() {
                 // TODO decrement all values
             }
diff --git a/compiler/gen/tests/gen_primitives.rs b/compiler/gen/tests/gen_primitives.rs
index aacf0715fa..865068f2f4 100644
--- a/compiler/gen/tests/gen_primitives.rs
+++ b/compiler/gen/tests/gen_primitives.rs
@@ -1206,11 +1206,11 @@ mod gen_primitives {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RedBlackTree k v : [ Node NodeColor k v (RedBlackTree k v) (RedBlackTree k v), Empty ]
 
                 Key k : Num k
 
-                insert : Key k, v, Dict (Key k) v -> Dict (Key k) v
+                insert : Key k, v, RedBlackTree (Key k) v -> RedBlackTree (Key k) v
                 insert = \key, value, dict ->
                     when insertHelp key value dict is
                         Node Red k v l r ->
@@ -1219,7 +1219,7 @@ mod gen_primitives {
                         x ->
                             x
 
-                insertHelp : (Key k), v, Dict (Key k) v -> Dict (Key k) v
+                insertHelp : (Key k), v, RedBlackTree (Key k) v -> RedBlackTree (Key k) v
                 insertHelp = \key, value, dict ->
                   when dict is
                     Empty ->
@@ -1238,7 +1238,7 @@ mod gen_primitives {
                         GT ->
                           balance nColor nKey nValue nLeft (insertHelp key value nRight)
 
-                balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                balance : NodeColor, k, v, RedBlackTree k v, RedBlackTree k v -> RedBlackTree k v
                 balance = \color, key, value, left, right ->
                   when right is
                     Node Red rK rV rLeft rRight ->
@@ -1267,7 +1267,7 @@ mod gen_primitives {
                         _ ->
                           Node color key value left right
 
-                main : Dict I64 {}
+                main : RedBlackTree I64 {}
                 main =
                     insert 0 {} Empty
                 "#
@@ -1288,9 +1288,9 @@ mod gen_primitives {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k : [ Node NodeColor k (Dict k)  (Dict k), Empty ]
+                RedBlackTree k : [ Node NodeColor k (RedBlackTree k)  (RedBlackTree k), Empty ]
 
-                # balance : NodeColor, k, Dict k,  Dict k -> Dict k
+                # balance : NodeColor, k, RedBlackTree k,  RedBlackTree k -> RedBlackTree k
                 balance = \color, key, left, right ->
                   when right is
                     Node Red rK rLeft rRight ->
@@ -1308,7 +1308,7 @@ mod gen_primitives {
                     _ ->
                         Empty
 
-                main : Dict I64
+                main : RedBlackTree I64
                 main =
                     balance Red 0 Empty Empty
                 "#
@@ -1325,13 +1325,13 @@ mod gen_primitives {
                 r#"
                 app "test" provides [ main ] to "./platform"
 
-                Dict k : [ Node k (Dict k) (Dict k), Empty ]
+                RedBlackTree k : [ Node k (RedBlackTree k) (RedBlackTree k), Empty ]
 
-                balance : k, Dict k -> Dict k
+                balance : k, RedBlackTree k -> RedBlackTree k
                 balance = \key, left ->
                     Node key left Empty
 
-                main : Dict I64
+                main : RedBlackTree I64
                 main =
                     balance 0 Empty
                 "#
@@ -1357,9 +1357,9 @@ mod gen_primitives {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RedBlackTree k v : [ Node NodeColor k v (RedBlackTree k v) (RedBlackTree k v), Empty ]
 
-                # balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                # balance : NodeColor, k, v, RedBlackTree k v, RedBlackTree k v -> RedBlackTree k v
                 balance = \color, key, value, left, right ->
                   when right is
                     Node Red rK rV rLeft rRight ->
@@ -1378,7 +1378,7 @@ mod gen_primitives {
                     _ ->
                         Empty
 
-                main : Dict I64 I64
+                main : RedBlackTree I64 I64
                 main =
                     balance Red 0 0 Empty Empty
                 "#
@@ -1397,9 +1397,9 @@ mod gen_primitives {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RedBlackTree k v : [ Node NodeColor k v (RedBlackTree k v) (RedBlackTree k v), Empty ]
 
-                balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                balance : NodeColor, k, v, RedBlackTree k v, RedBlackTree k v -> RedBlackTree k v
                 balance = \color, key, value, left, right ->
                   when right is
                     Node Red rK rV rLeft rRight ->
@@ -1428,7 +1428,7 @@ mod gen_primitives {
                         _ ->
                           Node color key value left right
 
-                main : Dict I64 I64
+                main : RedBlackTree I64 I64
                 main =
                     balance Red 0 0 Empty Empty
                 "#
diff --git a/compiler/load/tests/fixtures/build/interface_with_deps/AStar.roc b/compiler/load/tests/fixtures/build/interface_with_deps/AStar.roc
index b93c6937f3..4ddbb5946b 100644
--- a/compiler/load/tests/fixtures/build/interface_with_deps/AStar.roc
+++ b/compiler/load/tests/fixtures/build/interface_with_deps/AStar.roc
@@ -8,8 +8,8 @@ interface AStar
 Model position :
     { evaluated : Set position
     , openSet : Set position
-    , costs : Map.Map position F64
-    , cameFrom : Map.Map position position
+    , costs : Dict.Dict position F64
+    , cameFrom : Dict.Dict position position
     }
 
 
@@ -17,8 +17,8 @@ initialModel : position -> Model position
 initialModel = \start ->
     { evaluated : Set.empty
     , openSet : Set.singleton start
-    , costs : Map.singleton start 0.0
-    , cameFrom : Map.empty
+    , costs : Dict.singleton start 0.0
+    , cameFrom : Dict.empty
     }
 
 
@@ -26,7 +26,7 @@ cheapestOpen : (position -> F64), Model position -> Result position [ KeyNotFoun
 cheapestOpen = \costFunction, model ->
 
     folder = \position, resSmallestSoFar ->
-            when Map.get model.costs position is
+            when Dict.get model.costs position is
                 Err e ->
                     Err e
 
@@ -47,9 +47,9 @@ cheapestOpen = \costFunction, model ->
 
 
 
-reconstructPath : Map position position, position -> List position
+reconstructPath : Dict position position, position -> List position
 reconstructPath = \cameFrom, goal ->
-    when Map.get cameFrom goal is
+    when Dict.get cameFrom goal is
         Err KeyNotFound ->
             []
 
@@ -58,9 +58,9 @@ reconstructPath = \cameFrom, goal ->
 
 updateCost : position, position, Model position -> Model position
 updateCost = \current, neighbour, model ->
-    newCameFrom = Map.insert model.cameFrom neighbour current
+    newCameFrom = Dict.insert model.cameFrom neighbour current
 
-    newCosts = Map.insert model.costs neighbour distanceTo
+    newCosts = Dict.insert model.costs neighbour distanceTo
 
     distanceTo = reconstructPath newCameFrom neighbour
             |> List.len
@@ -68,7 +68,7 @@ updateCost = \current, neighbour, model ->
 
     newModel = { model & costs : newCosts , cameFrom : newCameFrom }
 
-    when Map.get model.costs neighbour is
+    when Dict.get model.costs neighbour is
         Err KeyNotFound ->
             newModel
 
diff --git a/compiler/load/tests/test_load.rs b/compiler/load/tests/test_load.rs
index 5d57bfa89a..b5be664eb6 100644
--- a/compiler/load/tests/test_load.rs
+++ b/compiler/load/tests/test_load.rs
@@ -242,15 +242,15 @@ mod test_load {
                 "RBTree",
                 indoc!(
                     r#"
-                        interface RBTree exposes [ Dict, empty ] imports []
+                        interface RBTree exposes [ RedBlackTree, empty ] imports []
 
                         # The color of a node. Leaves are considered Black.
                         NodeColor : [ Red, Black ]
 
-                        Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                        RedBlackTree k v : [ Node NodeColor k v (RedBlackTree k v) (RedBlackTree k v), Empty ]
 
                         # Create an empty dictionary.
-                        empty : Dict k v
+                        empty : RedBlackTree k v
                         empty =
                             Empty
                     "#
@@ -265,7 +265,7 @@ mod test_load {
                             imports [ RBTree ] 
                             provides [ main ] to blah
 
-                        empty : RBTree.Dict I64 I64
+                        empty : RBTree.RedBlackTree I64 I64
                         empty = RBTree.empty
 
                         main = empty
@@ -424,7 +424,7 @@ mod test_load {
             hashmap! {
                 "findPath" => "{ costFunction : position, position -> F64, end : position, moveFunction : position -> Set position, start : position } -> Result (List position) [ KeyNotFound ]*",
                 "initialModel" => "position -> Model position",
-                "reconstructPath" => "Map position position, position -> List position",
+                "reconstructPath" => "Dict position position, position -> List position",
                 "updateCost" => "position, position, Model position -> Model position",
                 "cheapestOpen" => "(position -> F64), Model position -> Result position [ KeyNotFound ]*",
                 "astar" => "(position, position -> F64), (position -> Set position), position, Model position -> [ Err [ KeyNotFound ]*, Ok (List position) ]*",
diff --git a/compiler/module/src/ident.rs b/compiler/module/src/ident.rs
index 438fa88060..409600f226 100644
--- a/compiler/module/src/ident.rs
+++ b/compiler/module/src/ident.rs
@@ -69,7 +69,7 @@ impl ModuleName {
     pub const STR: &'static str = "Str";
     pub const NUM: &'static str = "Num";
     pub const LIST: &'static str = "List";
-    pub const MAP: &'static str = "Map";
+    pub const DICT: &'static str = "Dict";
     pub const SET: &'static str = "Set";
     pub const RESULT: &'static str = "Result";
 
diff --git a/compiler/module/src/symbol.rs b/compiler/module/src/symbol.rs
index 2b3c2ca38f..3c6395c651 100644
--- a/compiler/module/src/symbol.rs
+++ b/compiler/module/src/symbol.rs
@@ -845,13 +845,13 @@ define_builtins! {
         0 RESULT_RESULT: "Result" imported // the Result.Result type alias
         1 RESULT_MAP: "map"
     }
-    6 MAP: "Map" => {
-        0 MAP_MAP: "Map" imported // the Map.Map type alias
-        1 MAP_AT_MAP: "@Map" // the Map.@Map private tag
-        2 MAP_EMPTY: "empty"
-        3 MAP_SINGLETON: "singleton"
-        4 MAP_GET: "get"
-        5 MAP_INSERT: "insert"
+    6 DICT: "Dict" => {
+        0 DICT_DICT: "Dict" imported // the Dict.Dict type alias
+        1 DICT_AT_DICT: "@Dict" // the Dict.@Dict private tag
+        2 DICT_EMPTY: "empty"
+        3 DICT_SINGLETON: "singleton"
+        4 DICT_GET: "get"
+        5 DICT_INSERT: "insert"
     }
     7 SET: "Set" => {
         0 SET_SET: "Set" imported // the Set.Set type alias
diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index 9e471d41d1..dbacb9fe64 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -587,7 +587,10 @@ impl<'a> Procs<'a> {
                 let symbol = name;
 
                 // TODO should pending_procs hold a Rc<Proc>?
-                let partial_proc = self.partial_procs.get(&symbol).unwrap().clone();
+                let partial_proc = match self.partial_procs.get(&symbol) {
+                    Some(p) => p.clone(),
+                    None => panic!("no partial_proc for {:?}", symbol),
+                };
 
                 // Mark this proc as in-progress, so if we're dealing with
                 // mutually recursive functions, we don't loop forever.
diff --git a/compiler/mono/src/layout.rs b/compiler/mono/src/layout.rs
index ce36477333..4b74489946 100644
--- a/compiler/mono/src/layout.rs
+++ b/compiler/mono/src/layout.rs
@@ -317,12 +317,12 @@ pub enum Builtin<'a> {
     Float32,
     Float16,
     Str,
-    Map(&'a Layout<'a>, &'a Layout<'a>),
+    Dict(&'a Layout<'a>, &'a Layout<'a>),
     Set(&'a Layout<'a>),
     List(MemoryMode, &'a Layout<'a>),
     EmptyStr,
     EmptyList,
-    EmptyMap,
+    EmptyDict,
     EmptySet,
 }
 
@@ -667,8 +667,8 @@ impl<'a> Builtin<'a> {
 
     /// Number of machine words in an empty one of these
     pub const STR_WORDS: u32 = 2;
-    pub const MAP_WORDS: u32 = 6;
-    pub const SET_WORDS: u32 = Builtin::MAP_WORDS; // Set is an alias for Map with {} for value
+    pub const DICT_WORDS: u32 = 6;
+    pub const SET_WORDS: u32 = Builtin::DICT_WORDS; // Set is an alias for Dict with {} for value
     pub const LIST_WORDS: u32 = 2;
 
     /// Layout of collection wrapper for List and Str - a struct of (pointer, length).
@@ -693,7 +693,7 @@ impl<'a> Builtin<'a> {
             Float32 => Builtin::F32_SIZE,
             Float16 => Builtin::F16_SIZE,
             Str | EmptyStr => Builtin::STR_WORDS * pointer_size,
-            Map(_, _) | EmptyMap => Builtin::MAP_WORDS * pointer_size,
+            Dict(_, _) | EmptyDict => Builtin::DICT_WORDS * pointer_size,
             Set(_) | EmptySet => Builtin::SET_WORDS * pointer_size,
             List(_, _) | EmptyList => Builtin::LIST_WORDS * pointer_size,
         }
@@ -718,7 +718,7 @@ impl<'a> Builtin<'a> {
             Float32 => align_of::<f32>() as u32,
             Float16 => align_of::<i16>() as u32,
             Str | EmptyStr => pointer_size,
-            Map(_, _) | EmptyMap => pointer_size,
+            Dict(_, _) | EmptyDict => pointer_size,
             Set(_) | EmptySet => pointer_size,
             List(_, _) | EmptyList => pointer_size,
         }
@@ -729,8 +729,8 @@ impl<'a> Builtin<'a> {
 
         match self {
             Int128 | Int64 | Int32 | Int16 | Int8 | Int1 | Float128 | Float64 | Float32
-            | Float16 | EmptyStr | EmptyMap | EmptyList | EmptySet => true,
-            Str | Map(_, _) | Set(_) | List(_, _) => false,
+            | Float16 | EmptyStr | EmptyDict | EmptyList | EmptySet => true,
+            Str | Dict(_, _) | Set(_) | List(_, _) => false,
         }
     }
 
@@ -740,13 +740,13 @@ impl<'a> Builtin<'a> {
 
         match self {
             Int128 | Int64 | Int32 | Int16 | Int8 | Int1 | Float128 | Float64 | Float32
-            | Float16 | EmptyStr | EmptyMap | EmptyList | EmptySet => false,
+            | Float16 | EmptyStr | EmptyDict | EmptyList | EmptySet => false,
             List(mode, element_layout) => match mode {
                 MemoryMode::Refcounted => true,
                 MemoryMode::Unique => element_layout.contains_refcounted(),
             },
 
-            Str | Map(_, _) | Set(_) => true,
+            Str | Dict(_, _) | Set(_) => true,
         }
     }
 }
diff --git a/compiler/mono/tests/test_mono.rs b/compiler/mono/tests/test_mono.rs
index 03cc907d56..be4bdc2950 100644
--- a/compiler/mono/tests/test_mono.rs
+++ b/compiler/mono/tests/test_mono.rs
@@ -269,14 +269,14 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.4 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.4;
 
                 procedure Test.0 ():
                     let Test.2 = 1i64;
                     let Test.3 = 2i64;
-                    let Test.1 = CallByName Num.14 Test.2 Test.3;
+                    let Test.1 = CallByName Num.24 Test.2 Test.3;
                     ret Test.1;
                 "#
             ),
@@ -291,13 +291,13 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.36 (#Attr.2):
+                procedure Num.46 (#Attr.2):
                     let Test.3 = lowlevel NumRound #Attr.2;
                     ret Test.3;
 
                 procedure Test.0 ():
                     let Test.2 = 3.6f64;
-                    let Test.1 = CallByName Num.36 Test.2;
+                    let Test.1 = CallByName Num.46 Test.2;
                     ret Test.1;
                 "#
             ),
@@ -314,7 +314,7 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.32 (#Attr.2, #Attr.3):
+                procedure Num.42 (#Attr.2, #Attr.3):
                     let Test.17 = 0i64;
                     let Test.13 = lowlevel NotEq #Attr.3 Test.17;
                     if Test.13 then
@@ -331,7 +331,7 @@ mod test_mono {
                 procedure Test.0 ():
                     let Test.8 = 1000i64;
                     let Test.9 = 10i64;
-                    let Test.2 = CallByName Num.32 Test.8 Test.9;
+                    let Test.2 = CallByName Num.42 Test.8 Test.9;
                     let Test.5 = 1i64;
                     let Test.6 = Index 0 Test.2;
                     let Test.7 = lowlevel Eq Test.5 Test.6;
@@ -357,14 +357,14 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.4 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.4;
 
                 procedure Test.0 ():
                     let Test.1 = 3i64;
                     let Test.2 = 4i64;
-                    let Test.3 = CallByName Num.14 Test.1 Test.2;
+                    let Test.3 = CallByName Num.24 Test.1 Test.2;
                     ret Test.3;
                 "#
             ),
@@ -384,7 +384,7 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.5 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.5;
 
@@ -398,7 +398,7 @@ mod test_mono {
                     if Test.9 then
                         let Test.2 = Index 1 Test.1;
                         let Test.4 = 1i64;
-                        let Test.3 = CallByName Num.14 Test.2 Test.4;
+                        let Test.3 = CallByName Num.24 Test.2 Test.4;
                         ret Test.3;
                     else
                         let Test.6 = 1i64;
@@ -480,7 +480,7 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.5 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.5;
 
@@ -489,7 +489,7 @@ mod test_mono {
                     let Test.2 = Struct {Test.6};
                     let Test.1 = Index 0 Test.2;
                     let Test.4 = 3i64;
-                    let Test.3 = CallByName Num.14 Test.1 Test.4;
+                    let Test.3 = CallByName Num.24 Test.1 Test.4;
                     ret Test.3;
                 "#
             ),
@@ -511,7 +511,7 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.6 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.6;
 
@@ -537,7 +537,7 @@ mod test_mono {
                             let Test.7 = Index 1 Test.2;
                             let Test.3 = Index 1 Test.7;
                             let Test.5 = 1i64;
-                            let Test.4 = CallByName Num.14 Test.3 Test.5;
+                            let Test.4 = CallByName Num.24 Test.3 Test.5;
                             ret Test.4;
                         else
                             jump Test.14;
@@ -558,7 +558,7 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.6 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.6;
 
@@ -569,7 +569,7 @@ mod test_mono {
                     joinpoint Test.11:
                         let Test.1 = Index 0 Test.3;
                         let Test.2 = Index 1 Test.3;
-                        let Test.5 = CallByName Num.14 Test.1 Test.2;
+                        let Test.5 = CallByName Num.24 Test.1 Test.2;
                         ret Test.5;
                     in
                     let Test.9 = Index 1 Test.3;
@@ -665,7 +665,7 @@ mod test_mono {
                     let Test.8 = lowlevel ListLen #Attr.2;
                     ret Test.8;
 
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.6 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.6;
 
@@ -680,7 +680,7 @@ mod test_mono {
                     dec Test.1;
                     let Test.5 = CallByName List.7 Test.2;
                     dec Test.2;
-                    let Test.3 = CallByName Num.14 Test.4 Test.5;
+                    let Test.3 = CallByName Num.24 Test.4 Test.5;
                     ret Test.3;
                 "#
             ),
@@ -1055,14 +1055,14 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.8 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.8;
 
                 procedure Test.1 (Test.2):
                     let Test.3 = Index 0 Test.2;
                     let Test.4 = Index 1 Test.2;
-                    let Test.7 = CallByName Num.14 Test.3 Test.4;
+                    let Test.7 = CallByName Num.24 Test.3 Test.4;
                     ret Test.7;
 
                 procedure Test.0 ():
@@ -1091,14 +1091,14 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.8 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.8;
 
                 procedure Test.1 (Test.2):
                     let Test.3 = 10i64;
                     let Test.4 = Index 1 Test.2;
-                    let Test.7 = CallByName Num.14 Test.3 Test.4;
+                    let Test.7 = CallByName Num.24 Test.3 Test.4;
                     ret Test.7;
 
                 procedure Test.0 ():
@@ -1124,14 +1124,14 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.8 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.8;
 
                 procedure Test.1 (Test.4):
                     let Test.2 = Index 0 Test.4;
                     let Test.3 = Index 1 Test.4;
-                    let Test.7 = CallByName Num.14 Test.2 Test.3;
+                    let Test.7 = CallByName Num.24 Test.2 Test.3;
                     ret Test.7;
 
                 procedure Test.0 ():
@@ -1158,14 +1158,14 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.8 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.8;
 
                 procedure Test.1 (Test.4):
                     let Test.2 = 10i64;
                     let Test.3 = Index 1 Test.4;
-                    let Test.7 = CallByName Num.14 Test.2 Test.3;
+                    let Test.7 = CallByName Num.24 Test.2 Test.3;
                     ret Test.7;
 
                 procedure Test.0 ():
@@ -1496,11 +1496,11 @@ mod test_mono {
             "#,
             indoc!(
                 r#"
-                procedure Num.15 (#Attr.2, #Attr.3):
+                procedure Num.25 (#Attr.2, #Attr.3):
                     let Test.14 = lowlevel NumSub #Attr.2 #Attr.3;
                     ret Test.14;
 
-                procedure Num.16 (#Attr.2, #Attr.3):
+                procedure Num.26 (#Attr.2, #Attr.3):
                     let Test.12 = lowlevel NumMul #Attr.2 #Attr.3;
                     ret Test.12;
 
@@ -1512,8 +1512,8 @@ mod test_mono {
                             ret Test.3;
                         else
                             let Test.13 = 1i64;
-                            let Test.10 = CallByName Num.15 Test.2 Test.13;
-                            let Test.11 = CallByName Num.16 Test.2 Test.3;
+                            let Test.10 = CallByName Num.25 Test.2 Test.13;
+                            let Test.11 = CallByName Num.26 Test.2 Test.3;
                             jump Test.7 Test.10 Test.11;
                     in
                     jump Test.7 Test.2 Test.3;
@@ -1715,7 +1715,7 @@ mod test_mono {
                     let Test.9 = lowlevel ListLen #Attr.2;
                     ret Test.9;
 
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.7 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.7;
 
@@ -1740,7 +1740,7 @@ mod test_mono {
                     let Test.8 = FunctionPointer Test.1;
                     let Test.6 = CallByName List.7 Test.8;
                     dec Test.8;
-                    let Test.4 = CallByName Num.14 Test.5 Test.6;
+                    let Test.4 = CallByName Num.24 Test.5 Test.6;
                     ret Test.4;
                 "#
             ),
@@ -1935,7 +1935,7 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.16 (#Attr.2, #Attr.3):
+                procedure Num.26 (#Attr.2, #Attr.3):
                     let Test.13 = lowlevel NumMul #Attr.2 #Attr.3;
                     ret Test.13;
 
@@ -1976,9 +1976,9 @@ mod test_mono {
                     let Test.22 = false;
                     let Test.15 = Struct {Test.21, Test.22};
                     let Test.2 = CallByName Test.1 Test.15;
-                    let Test.14 = CallByName Num.16 Test.2 Test.3;
-                    let Test.12 = CallByName Num.16 Test.14 Test.4;
-                    let Test.11 = CallByName Num.16 Test.12 Test.5;
+                    let Test.14 = CallByName Num.26 Test.2 Test.3;
+                    let Test.12 = CallByName Num.26 Test.14 Test.4;
+                    let Test.11 = CallByName Num.26 Test.12 Test.5;
                     ret Test.11;
                 "#
             ),
@@ -2002,7 +2002,7 @@ mod test_mono {
             ),
             indoc!(
                 r#"
-                procedure Num.14 (#Attr.2, #Attr.3):
+                procedure Num.24 (#Attr.2, #Attr.3):
                     let Test.6 = lowlevel NumAdd #Attr.2 #Attr.3;
                     ret Test.6;
 
@@ -2028,7 +2028,7 @@ mod test_mono {
                             let Test.7 = Index 1 Test.2;
                             let Test.3 = Index 1 Test.7;
                             let Test.5 = 1i64;
-                            let Test.4 = CallByName Num.14 Test.3 Test.5;
+                            let Test.4 = CallByName Num.24 Test.3 Test.5;
                             ret Test.4;
                         else
                             jump Test.14;
diff --git a/compiler/reporting/tests/test_reporting.rs b/compiler/reporting/tests/test_reporting.rs
index 6f394ac6fd..0f3b3dfc56 100644
--- a/compiler/reporting/tests/test_reporting.rs
+++ b/compiler/reporting/tests/test_reporting.rs
@@ -447,9 +447,9 @@ mod test_reporting {
                 these names seem close though:
 
                     baz
-                    Map
                     Str
                     main
+                    U8
                 "#
             ),
         )
@@ -3534,8 +3534,8 @@ mod test_reporting {
 
                     Bool
                     Num
-                    Map
                     Set
+                    Str
                 "#
             ),
         )
@@ -3928,10 +3928,10 @@ mod test_reporting {
                 # The color of a node. Leaves are considered Black.
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RBTree k v : [ Node NodeColor k v (RBTree k v) (RBTree k v), Empty ]
 
                 # Create an empty dictionary.
-                empty : Dict k v
+                empty : RBTree k v
                 empty =
                     Empty
 
diff --git a/compiler/solve/tests/solve_expr.rs b/compiler/solve/tests/solve_expr.rs
index a651fa05f1..835473f518 100644
--- a/compiler/solve/tests/solve_expr.rs
+++ b/compiler/solve/tests/solve_expr.rs
@@ -3102,10 +3102,10 @@ mod solve_expr {
         infer_eq_without_problem(
             indoc!(
                 r#"
-                Map.insert
+                Dict.insert
                 "#
             ),
-            "Map a b, a, b -> Map a b",
+            "Dict a b, a, b -> Dict a b",
         );
     }
 
@@ -3186,9 +3186,9 @@ mod solve_expr {
         infer_eq_without_problem(
             indoc!(
                 r#"
-                reconstructPath : Map position position, position -> List position
+                reconstructPath : Dict position position, position -> List position
                 reconstructPath = \cameFrom, goal ->
-                    when Map.get cameFrom goal is
+                    when Dict.get cameFrom goal is
                         Err KeyNotFound ->
                             []
 
@@ -3198,7 +3198,7 @@ mod solve_expr {
                 reconstructPath
                 "#
             ),
-            "Map position position, position -> List position",
+            "Dict position position, position -> List position",
         );
     }
 
@@ -3695,22 +3695,22 @@ mod solve_expr {
                 # The color of a node. Leaves are considered Black.
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RBTree k v : [ Node NodeColor k v (RBTree k v) (RBTree k v), Empty ]
 
                 # Create an empty dictionary.
-                empty : Dict k v
+                empty : RBTree k v
                 empty =
                     Empty
 
-                foo : Dict I64 I64
+                foo : RBTree I64 I64
                 foo = empty
 
-                main : Dict I64 I64
+                main : RBTree I64 I64
                 main =
                     foo
                 "#
             ),
-            "Dict I64 I64",
+            "RBTree I64 I64",
         );
     }
 
@@ -3725,21 +3725,21 @@ mod solve_expr {
                 r#"
                 app "test" provides [ main ] to "./platform"
 
-                Dict k : [ Node k (Dict k), Empty ]
+                RBTree k : [ Node k (RBTree k), Empty ]
 
-                balance : Dict k -> Dict k
+                balance : RBTree  k -> RBTree k
                 balance = \left ->
                     when left is
                       Node _ Empty -> Empty
 
                       _ -> Empty
 
-                main : Dict {}
+                main : RBTree {}
                 main =
                     balance Empty
                 "#
             ),
-            "Dict {}",
+            "RBTree {}",
         );
     }
 
@@ -3752,9 +3752,9 @@ mod solve_expr {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RBTree k v : [ Node NodeColor k v (RBTree k v) (RBTree k v), Empty ]
 
-                moveRedLeft : Dict k v -> Dict k v
+                moveRedLeft : RBTree k v -> RBTree k v
                 moveRedLeft = \dict ->
                   when dict is
                     # Node clr k v (Node lClr lK lV lLeft lRight) (Node rClr rK rV ((Node Red rlK rlV rlL rlR) as rLeft) rRight) ->
@@ -3790,7 +3790,7 @@ mod solve_expr {
                     _ ->
                       dict
 
-                balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                balance : NodeColor, k, v, RBTree k v, RBTree k v -> RBTree k v
                 balance = \color, key, value, left, right ->
                   when right is
                     Node Red rK rV rLeft rRight ->
@@ -3822,7 +3822,7 @@ mod solve_expr {
 
                 Key k : Num k
 
-                removeHelpEQGT : Key k, Dict (Key k) v -> Dict (Key k) v
+                removeHelpEQGT : Key k, RBTree (Key k) v -> RBTree (Key k) v
                 removeHelpEQGT = \targetKey, dict ->
                   when dict is
                     Node color key value left right ->
@@ -3839,7 +3839,7 @@ mod solve_expr {
                     Empty ->
                       Empty
 
-                getMin : Dict k v -> Dict k v
+                getMin : RBTree k v -> RBTree k v
                 getMin = \dict ->
                   when dict is
                     # Node _ _ _ ((Node _ _ _ _ _) as left) _ ->
@@ -3852,7 +3852,7 @@ mod solve_expr {
                       dict
 
 
-                moveRedRight : Dict k v -> Dict k v
+                moveRedRight : RBTree k v -> RBTree k v
                 moveRedRight = \dict ->
                   when dict is
                     Node clr k v (Node lClr lK lV (Node Red llK llV llLeft llRight) lRight) (Node rClr rK rV rLeft rRight) ->
@@ -3885,7 +3885,7 @@ mod solve_expr {
                       dict
 
 
-                removeHelpPrepEQGT : Key k, Dict (Key k) v, NodeColor, (Key k), v, Dict (Key k) v, Dict (Key k) v -> Dict (Key k) v
+                removeHelpPrepEQGT : Key k, RBTree (Key k) v, NodeColor, (Key k), v, RBTree (Key k) v, RBTree (Key k) v -> RBTree (Key k) v
                 removeHelpPrepEQGT = \_, dict, color, key, value, left, right ->
                   when left is
                     Node Red lK lV lLeft lRight ->
@@ -3908,7 +3908,7 @@ mod solve_expr {
                           dict
 
 
-                removeMin : Dict k v -> Dict k v
+                removeMin : RBTree k v -> RBTree k v
                 removeMin = \dict ->
                   when dict is
                     Node color key value left right ->
@@ -3936,7 +3936,7 @@ mod solve_expr {
                     _ ->
                       Empty
 
-                removeHelp : Key k, Dict (Key k) v -> Dict (Key k) v
+                removeHelp : Key k, RBTree (Key k) v -> RBTree (Key k) v
                 removeHelp = \targetKey, dict ->
                   when dict is
                     Empty ->
@@ -3964,12 +3964,12 @@ mod solve_expr {
                         removeHelpEQGT targetKey (removeHelpPrepEQGT targetKey dict color key value left right)
 
 
-                main : Dict I64 I64
+                main : RBTree I64 I64
                 main =
                     removeHelp 1 Empty
                 "#
             ),
-            "Dict I64 I64",
+            "RBTree I64 I64",
         );
     }
 
@@ -3980,9 +3980,9 @@ mod solve_expr {
                 r#"
                 app "test" provides [ main ] to "./platform"
 
-                Dict k : [ Node k (Dict k) (Dict k), Empty ]
+                RBTree k : [ Node k (RBTree k) (RBTree k), Empty ]
 
-                removeHelp : Num k, Dict (Num k) -> Dict (Num k)
+                removeHelp : Num k, RBTree (Num k) -> RBTree (Num k)
                 removeHelp = \targetKey, dict ->
                   when dict is
                     Empty ->
@@ -4004,12 +4004,12 @@ mod solve_expr {
                         Empty
 
 
-                main : Dict I64
+                main : RBTree I64
                 main =
                     removeHelp 1 Empty
                 "#
             ),
-            "Dict I64",
+            "RBTree I64",
         );
     }
 
@@ -4022,9 +4022,9 @@ mod solve_expr {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RBTree k v : [ Node NodeColor k v (RBTree k v) (RBTree k v), Empty ]
 
-                removeHelp : Num k, Dict (Num k) v -> Dict (Num k) v
+                removeHelp : Num k, RBTree (Num k) v -> RBTree (Num k) v
                 removeHelp = \targetKey, dict ->
                   when dict is
                     Empty ->
@@ -4053,13 +4053,13 @@ mod solve_expr {
 
                 Key k : Num k
 
-                balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                balance : NodeColor, k, v, RBTree k v, RBTree k v -> RBTree k v
 
-                moveRedLeft : Dict k v -> Dict k v
+                moveRedLeft : RBTree k v -> RBTree k v
 
-                removeHelpPrepEQGT : Key k, Dict (Key k) v, NodeColor, (Key k), v, Dict (Key k) v, Dict (Key k) v -> Dict (Key k) v
+                removeHelpPrepEQGT : Key k, RBTree (Key k) v, NodeColor, (Key k), v, RBTree (Key k) v, RBTree (Key k) v -> RBTree (Key k) v
 
-                removeHelpEQGT : Key k, Dict (Key k) v -> Dict (Key k) v
+                removeHelpEQGT : Key k, RBTree (Key k) v -> RBTree (Key k) v
                 removeHelpEQGT = \targetKey, dict ->
                   when dict is
                     Node color key value left right ->
@@ -4076,16 +4076,16 @@ mod solve_expr {
                     Empty ->
                       Empty
 
-                getMin : Dict k v -> Dict k v
+                getMin : RBTree k v -> RBTree k v
 
-                removeMin : Dict k v -> Dict k v
+                removeMin : RBTree k v -> RBTree k v
 
-                main : Dict I64 I64
+                main : RBTree I64 I64
                 main =
                     removeHelp 1 Empty
                 "#
             ),
-            "Dict I64 I64",
+            "RBTree I64 I64",
         );
     }
 
@@ -4134,18 +4134,18 @@ mod solve_expr {
                 r#"
                 app "test" provides [ main ] to "./platform"
 
-                Dict k : [ Node k (Dict k) (Dict k), Empty ]
+                RBTree k : [ Node k (RBTree k) (RBTree k), Empty ]
 
-                balance : k, Dict k -> Dict k
+                balance : k, RBTree k -> RBTree k
                 balance = \key, left ->
                     Node key left Empty
 
-                main : Dict I64
+                main : RBTree I64
                 main =
                     balance 0 Empty
                 "#
             ),
-            "Dict I64",
+            "RBTree I64",
         );
     }
 
@@ -4156,20 +4156,20 @@ mod solve_expr {
                 r#"
                 app "test" provides [ main ] to "./platform"
 
-                Dict k : [ Node k (Dict k) (Dict k), Empty ]
+                RBTree k : [ Node k (RBTree k) (RBTree k), Empty ]
 
                 node = \x,y,z -> Node x y z
 
-                balance : k, Dict k -> Dict k
+                balance : k, RBTree k -> RBTree k
                 balance = \key, left ->
                     node key left Empty
 
-                main : Dict I64
+                main : RBTree I64
                 main =
                     balance 0 Empty
                 "#
             ),
-            "Dict I64",
+            "RBTree I64",
         );
     }
 
@@ -4182,9 +4182,9 @@ mod solve_expr {
 
                 NodeColor : [ Red, Black ]
 
-                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+                RBTree k v : [ Node NodeColor k v (RBTree k v) (RBTree k v), Empty ]
 
-                balance : NodeColor, k, v, Dict k v, Dict k v -> Dict k v
+                balance : NodeColor, k, v, RBTree k v, RBTree k v -> RBTree k v
                 balance = \color, key, value, left, right ->
                   when right is
                     Node Red rK rV rLeft rRight ->
@@ -4213,12 +4213,12 @@ mod solve_expr {
                         _ ->
                           Node color key value left right
 
-                main : Dict I64 I64
+                main : RBTree I64 I64
                 main =
                     balance Red 0 0 Empty Empty
                 "#
             ),
-            "Dict I64 I64",
+            "RBTree I64 I64",
         );
     }
 
@@ -4230,9 +4230,9 @@ mod solve_expr {
                 r#"
                 app Test provides [ main ] imports []
 
-                Dict k : [ Node k (Dict k) (Dict k), Empty ]
+                RBTree k : [ Node k (RBTree k) (RBTree k), Empty ]
 
-                balance : k, Dict k -> Dict k
+                balance : k, RBTree k -> RBTree k
                 balance = \key, left ->
                       when left is
                         Node _ _ lRight ->
@@ -4242,12 +4242,12 @@ mod solve_expr {
                             Empty
 
 
-                main : Dict I64
+                main : RBTree I64
                 main =
                     balance 0 Empty
                 "#
             ),
-            "Dict I64",
+            "RBTree I64",
         );
     }
 }
diff --git a/compiler/solve/tests/solve_uniq_expr.rs b/compiler/solve/tests/solve_uniq_expr.rs
index cfc0ed1c7a..adf9f098bf 100644
--- a/compiler/solve/tests/solve_uniq_expr.rs
+++ b/compiler/solve/tests/solve_uniq_expr.rs
@@ -2397,24 +2397,24 @@ mod solve_uniq_expr {
 
     #[test]
     fn map_empty() {
-        infer_eq("Map.empty", "Attr * (Map * *)");
+        infer_eq("Dict.empty", "Attr * (Dict * *)");
     }
 
     #[test]
     fn map_singelton() {
-        infer_eq("Map.singleton", "Attr * (a, b -> Attr * (Map a b))");
+        infer_eq("Dict.singleton", "Attr * (a, b -> Attr * (Dict a b))");
     }
 
     #[test]
     fn map_get() {
-        infer_eq("Map.get", "Attr * (Attr (* | c) (Map (Attr * a) (Attr c b)), Attr * a -> Attr * (Result (Attr c b) (Attr * [ KeyNotFound ]*)))");
+        infer_eq("Dict.get", "Attr * (Attr (* | c) (Dict (Attr * a) (Attr c b)), Attr * a -> Attr * (Result (Attr c b) (Attr * [ KeyNotFound ]*)))");
     }
 
     #[test]
     fn map_insert() {
         infer_eq(
-            "Map.insert",
-            "Attr * (Attr * (Map a b), a, b -> Attr * (Map a b))",
+            "Dict.insert",
+            "Attr * (Attr * (Dict a b), a, b -> Attr * (Dict a b))",
         );
     }
 
@@ -2747,9 +2747,9 @@ mod solve_uniq_expr {
         infer_eq(
             indoc!(
                 r#"
-                reconstructPath : Map position position, position -> List position
+                reconstructPath : Dict position position, position -> List position
                 reconstructPath = \cameFrom, goal ->
-                    when Map.get cameFrom goal is
+                    when Dict.get cameFrom goal is
                         Err KeyNotFound ->
                             []
 
@@ -2759,7 +2759,7 @@ mod solve_uniq_expr {
                 reconstructPath
                 "#
             ),
-            "Attr Shared (Attr Shared (Map (Attr * position) (Attr Shared position)), Attr Shared position -> Attr * (List (Attr Shared position)))"
+            "Attr Shared (Attr Shared (Dict (Attr * position) (Attr Shared position)), Attr Shared position -> Attr * (List (Attr Shared position)))"
         );
     }
 
@@ -2772,15 +2772,15 @@ mod solve_uniq_expr {
                 r#"
                 Model position : { evaluated : Set position
                     , openSet : Set  position
-                    , costs : Map.Map position F64
-                    , cameFrom : Map.Map position position
+                    , costs : Dict.Dict position F64
+                    , cameFrom : Dict.Dict position position
                     }
 
                 cheapestOpen : (position -> F64), Model position -> Result position [ KeyNotFound ]*
                 cheapestOpen = \costFunction, model ->
 
                     folder = \position, resSmallestSoFar ->
-                            when Map.get model.costs position is
+                            when Dict.get model.costs position is
                                 Err e ->
                                     Err e
 
@@ -2815,13 +2815,13 @@ mod solve_uniq_expr {
                 r#"
                 Model position : { evaluated : Set position
                     , openSet : Set  position
-                    , costs : Map.Map position F64
-                    , cameFrom : Map.Map position position
+                    , costs : Dict.Dict position F64
+                    , cameFrom : Dict.Dict position position
                     }
 
-                reconstructPath : Map position position, position -> List position
+                reconstructPath : Dict position position, position -> List position
                 reconstructPath = \cameFrom, goal ->
-                    when Map.get cameFrom goal is
+                    when Dict.get cameFrom goal is
                         Err KeyNotFound ->
                             []
 
@@ -2830,9 +2830,9 @@ mod solve_uniq_expr {
 
                 updateCost : position, position, Model position -> Model position
                 updateCost = \current, neighbour, model ->
-                    newCameFrom = Map.insert model.cameFrom neighbour current
+                    newCameFrom = Dict.insert model.cameFrom neighbour current
 
-                    newCosts = Map.insert model.costs neighbour distanceTo
+                    newCosts = Dict.insert model.costs neighbour distanceTo
 
                     distanceTo = reconstructPath newCameFrom neighbour
                             |> List.len
@@ -2840,7 +2840,7 @@ mod solve_uniq_expr {
 
                     newModel = { model & costs : newCosts , cameFrom : newCameFrom }
 
-                    when Map.get model.costs neighbour is
+                    when Dict.get model.costs neighbour is
                         Err KeyNotFound ->
                             newModel
 
@@ -2867,8 +2867,8 @@ mod solve_uniq_expr {
                 r#"
                     Model position : { evaluated : Set position
                         , openSet : Set  position
-                        , costs : Map.Map position F64
-                        , cameFrom : Map.Map position position
+                        , costs : Dict.Dict position F64
+                        , cameFrom : Dict.Dict position position
                         }
 
 
@@ -2876,8 +2876,8 @@ mod solve_uniq_expr {
                     initialModel = \start ->
                         { evaluated : Set.empty
                         , openSet : Set.singleton start
-                        , costs : Map.singleton start 0.0
-                        , cameFrom : Map.empty
+                        , costs : Dict.singleton start 0.0
+                        , cameFrom : Dict.empty
                         }
 
 
@@ -2885,7 +2885,7 @@ mod solve_uniq_expr {
                     cheapestOpen = \costFunction, model ->
 
                         folder = \position, resSmallestSoFar ->
-                            when Map.get model.costs position is
+                            when Dict.get model.costs position is
                                 Err e ->
                                     Err e
 
@@ -2906,9 +2906,9 @@ mod solve_uniq_expr {
                             |> Result.map (\x -> x.position)
 
 
-                    reconstructPath : Map position position, position -> List position
+                    reconstructPath : Dict position position, position -> List position
                     reconstructPath = \cameFrom, goal ->
-                        when Map.get cameFrom goal is
+                        when Dict.get cameFrom goal is
                             Err KeyNotFound ->
                                 []
 
@@ -2918,9 +2918,9 @@ mod solve_uniq_expr {
 
                     updateCost : position, position, Model position -> Model position
                     updateCost = \current, neighbour, model ->
-                        newCameFrom = Map.insert model.cameFrom neighbour current
+                        newCameFrom = Dict.insert model.cameFrom neighbour current
 
-                        newCosts = Map.insert model.costs neighbour distanceTo
+                        newCosts = Dict.insert model.costs neighbour distanceTo
 
                         distanceTo =
                             reconstructPath newCameFrom neighbour
@@ -2929,7 +2929,7 @@ mod solve_uniq_expr {
 
                         newModel = { model & costs : newCosts , cameFrom : newCameFrom }
 
-                        when Map.get model.costs neighbour is
+                        when Dict.get model.costs neighbour is
                             Err KeyNotFound ->
                                 newModel
 
diff --git a/compiler/types/src/builtin_aliases.rs b/compiler/types/src/builtin_aliases.rs
index 280386fc28..885d9fa395 100644
--- a/compiler/types/src/builtin_aliases.rs
+++ b/compiler/types/src/builtin_aliases.rs
@@ -347,8 +347,8 @@ pub fn set_type(a: SolvedType) -> SolvedType {
 }
 
 #[inline(always)]
-pub fn map_type(key: SolvedType, value: SolvedType) -> SolvedType {
-    SolvedType::Apply(Symbol::MAP_MAP, vec![key, value])
+pub fn dict_type(key: SolvedType, value: SolvedType) -> SolvedType {
+    SolvedType::Apply(Symbol::DICT_DICT, vec![key, value])
 }
 
 fn single_private_tag(symbol: Symbol, type_arguments: Vec<SolvedType>) -> SolvedType {
diff --git a/compiler/types/src/types.rs b/compiler/types/src/types.rs
index 4d07aa859d..ac62591a15 100644
--- a/compiler/types/src/types.rs
+++ b/compiler/types/src/types.rs
@@ -150,7 +150,7 @@ pub enum Type {
         actual: Box<Type>,
     },
     RecursiveTagUnion(Variable, Vec<(TagName, Vec<Type>)>, Box<Type>),
-    /// Applying a type to some arguments (e.g. Map.Map String Int)
+    /// Applying a type to some arguments (e.g. Dict.Dict String Int)
     Apply(Symbol, Vec<Type>),
     /// Boolean type used in uniqueness inference
     Boolean(boolean_algebra::Bool),
diff --git a/docs/src/main.rs b/docs/src/main.rs
index 256978028e..8e644c9780 100644
--- a/docs/src/main.rs
+++ b/docs/src/main.rs
@@ -48,7 +48,7 @@ fn main() {
     generate(
         vec![
             PathBuf::from(r"../compiler/builtins/docs/Bool.roc"),
-            PathBuf::from(r"../compiler/builtins/docs/Map.roc"),
+            PathBuf::from(r"../compiler/builtins/docs/Dict.roc"),
             // Not working
             // PathBuf::from(r"../compiler/builtins/docs/List.roc"),
             // Not working
diff --git a/examples/tea/Main.roc b/examples/tea/Main.roc
new file mode 100644
index 0000000000..6a02b55825
--- /dev/null
+++ b/examples/tea/Main.roc
@@ -0,0 +1,7 @@
+app "effect-example"
+    packages { base: "platform" }
+    imports [base.Cmd]
+    provides [ main ] to base
+
+main : I64 
+main = 42 
diff --git a/examples/tea/platform/Cargo.lock b/examples/tea/platform/Cargo.lock
new file mode 100644
index 0000000000..331efb48b9
--- /dev/null
+++ b/examples/tea/platform/Cargo.lock
@@ -0,0 +1,21 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "host"
+version = "0.1.0"
+dependencies = [
+ "roc_std",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.81"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1482821306169ec4d07f6aca392a4681f66c75c9918aa49641a2595db64053cb"
+
+[[package]]
+name = "roc_std"
+version = "0.1.0"
+dependencies = [
+ "libc",
+]
diff --git a/examples/tea/platform/Cargo.toml b/examples/tea/platform/Cargo.toml
new file mode 100644
index 0000000000..70f3c1f86c
--- /dev/null
+++ b/examples/tea/platform/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "host"
+version = "0.1.0"
+authors = ["Richard Feldman <oss@rtfeldman.com>"]
+edition = "2018"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+roc_std = { path = "../../../roc_std" }
+
+[workspace]
diff --git a/examples/tea/platform/Cmd.roc b/examples/tea/platform/Cmd.roc
new file mode 100644
index 0000000000..cb0a78b1cc
--- /dev/null
+++ b/examples/tea/platform/Cmd.roc
@@ -0,0 +1,24 @@
+interface Cmd
+    exposes [ Cmd, none, map, putLine, getLine, always, after ]
+    imports [ Effect ]
+
+Cmd a : Effect.Effect a
+
+none : Cmd {}
+none = Effect.always {}
+
+always : {} -> Cmd {}
+always = \x -> Effect.always x
+
+getLine : (Str -> msg) -> Cmd msg
+getLine = \toMsg ->
+    Effect.map Effect.getLine toMsg
+
+putLine : Str -> Cmd {}
+putLine = \line -> Effect.putLine line 
+
+map : Cmd a, (a -> b) -> Cmd b
+map = \cmd, transform -> Effect.map cmd transform
+
+after : Cmd a, (a -> Cmd b) -> Cmd b
+after = \cmd, transform -> Effect.after cmd transform
diff --git a/examples/tea/platform/Pkg-Config.roc b/examples/tea/platform/Pkg-Config.roc
new file mode 100644
index 0000000000..6d9a0a0752
--- /dev/null
+++ b/examples/tea/platform/Pkg-Config.roc
@@ -0,0 +1,41 @@
+platform folkertdev/foo
+    requires { main : Effect {} }
+    exposes []
+    packages {}
+    imports [Cmd]
+    provides [ mainForHost ]
+    effects Effect
+        {
+            putChar : I64 -> Effect {},
+            putLine : Str -> Effect {},
+            getLine : Effect Str
+        }
+
+
+mainForHost : 
+    {
+        init : ({} -> { model: I64, cmd : (Cmd.Cmd [ Line Str ]) as Fx }) as Init,
+        update : ([ Line Str ], I64 -> { model: I64, cmd : Cmd.Cmd [ Line Str ] } ) as Update
+    }
+mainForHost = 
+    { 
+        init : \{} -> 
+            { 
+                model: 42,
+                cmd: 
+                    Cmd.after (Cmd.putLine "Type a thing, and I'll say it back") \{} -> 
+                        Cmd.getLine (\l -> Line l) 
+            },
+        update : \msg, model -> 
+            when msg is
+                Line line -> 
+                    cmd = 
+                        Cmd.after (Cmd.putLine "You said:") \{} ->                             
+                        Cmd.after (Cmd.putLine line) \{} ->                             
+                        Cmd.after (Cmd.putLine "Type another thing, and I'll say it back") \{} ->                             
+                        Cmd.getLine (\l -> Line l) 
+
+                    { model: model + 1, cmd }
+    }
+
+
diff --git a/examples/tea/platform/host.c b/examples/tea/platform/host.c
new file mode 100644
index 0000000000..0378c69589
--- /dev/null
+++ b/examples/tea/platform/host.c
@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+extern int rust_main();
+
+int main() {
+  return rust_main();
+}
diff --git a/examples/tea/platform/src/lib.rs b/examples/tea/platform/src/lib.rs
new file mode 100644
index 0000000000..3d9efe668d
--- /dev/null
+++ b/examples/tea/platform/src/lib.rs
@@ -0,0 +1,298 @@
+#![allow(non_snake_case)]
+
+use roc_std::alloca;
+use roc_std::RocCallResult;
+use roc_std::RocStr;
+use std::alloc::Layout;
+use std::time::SystemTime;
+
+type Msg = RocStr;
+type Model = i64;
+
+extern "C" {
+    #[link_name = "roc__mainForHost_1_exposed"]
+    fn roc_main(output: *mut u8) -> ();
+
+    #[link_name = "roc__mainForHost_1_size"]
+    fn roc_main_size() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Init_caller"]
+    fn call_Init(function_pointer: *const u8, closure_data: *const u8, output: *mut u8) -> ();
+
+    #[link_name = "roc__mainForHost_1_Init_size"]
+    fn size_Init() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Init_result_size"]
+    fn size_Init_result() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Update_caller"]
+    fn call_Update(
+        msg: Msg,
+        model: Model,
+        function_pointer: *const u8,
+        closure_data: *const u8,
+        output: *mut u8,
+    ) -> ();
+
+    #[link_name = "roc__mainForHost_1_Update_size"]
+    fn size_Update() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Update_result_size"]
+    fn size_Update_result() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Fx_caller"]
+    fn call_Fx(function_pointer: *const u8, closure_data: *const u8, output: *mut u8) -> ();
+
+    #[link_name = "roc__mainForHost_1_Fx_size"]
+    fn size_Fx() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Fx_result_size"]
+    fn size_Fx_result() -> i64;
+
+    #[link_name = "roc__mainForHost_1_Model_size"]
+    fn size_Model() -> i64;
+}
+
+#[no_mangle]
+pub fn roc_fx_putChar(foo: i64) -> () {
+    let character = foo as u8 as char;
+    print!("{}", character);
+
+    ()
+}
+
+#[no_mangle]
+pub fn roc_fx_putLine(line: RocStr) -> () {
+    let bytes = line.as_slice();
+    let string = unsafe { std::str::from_utf8_unchecked(bytes) };
+    println!("{}", string);
+
+    ()
+}
+
+#[no_mangle]
+pub fn roc_fx_getLine() -> RocStr {
+    use std::io::{self, BufRead};
+
+    let stdin = io::stdin();
+    let line1 = stdin.lock().lines().next().unwrap().unwrap();
+
+    RocStr::from_slice_with_capacity(line1.as_bytes(), line1.len())
+}
+
+unsafe fn run_fx(function_pointer: *const u8, closure_data_ptr: *const u8) -> Msg {
+    let size = size_Fx_result() as usize;
+
+    alloca::with_stack_bytes(size, |buffer| {
+        let buffer: *mut std::ffi::c_void = buffer;
+        let buffer: *mut u8 = buffer as *mut u8;
+
+        call_Fx(
+            function_pointer,
+            closure_data_ptr as *const u8,
+            buffer as *mut u8,
+        );
+
+        let output = &*(buffer as *mut RocCallResult<()>);
+
+        match output.into() {
+            Ok(()) => {
+                let mut bytes = *(buffer.add(8) as *const (u64, u64));
+                let msg = std::mem::transmute::<(u64, u64), RocStr>(bytes);
+
+                msg
+            }
+
+            Err(e) => panic!("failed with {}", e),
+        }
+    })
+}
+
+unsafe fn run_init(function_pointer: *const u8, closure_data_ptr: *const u8) -> (Model, Msg) {
+    let size = size_Init_result() as usize;
+
+    alloca::with_stack_bytes(size, |buffer| {
+        let buffer: *mut std::ffi::c_void = buffer;
+        let buffer: *mut u8 = buffer as *mut u8;
+
+        call_Init(function_pointer, 0 as *const u8, buffer as *mut u8);
+
+        // cmd < model, so the command comes first
+        let output = &*(buffer as *mut RocCallResult<()>);
+
+        match output.into() {
+            Ok(_) => {
+                let offset = 8 + size_Fx();
+                let model_ptr = buffer.add(offset as usize);
+                let model: i64 = *(model_ptr as *const i64);
+
+                let cmd_fn_ptr_ptr = buffer.add(8) as *const i64;
+                let cmd_fn_ptr = (*cmd_fn_ptr_ptr) as *const u8;
+                let cmd_closure_data_ptr = buffer.add(16);
+
+                let msg = run_fx(cmd_fn_ptr, cmd_closure_data_ptr);
+
+                (model, msg)
+            }
+
+            Err(e) => panic!("failed with {}", e),
+        }
+    })
+}
+
+unsafe fn run_update(
+    msg: RocStr,
+    model: Model,
+    function_pointer: *const u8,
+    closure_data_ptr: *const u8,
+) -> (Model, Msg) {
+    let size = size_Update_result() as usize;
+
+    alloca::with_stack_bytes(size, |buffer| {
+        let buffer: *mut std::ffi::c_void = buffer;
+        let buffer: *mut u8 = buffer as *mut u8;
+
+        call_Update(
+            msg,
+            model,
+            function_pointer,
+            closure_data_ptr,
+            buffer as *mut u8,
+        );
+
+        // cmd < model, so the command comes first
+        let output = &*(buffer as *mut RocCallResult<()>);
+
+        match output.into() {
+            Ok(_) => {
+                let offset = 8 + size_Fx();
+                let model_ptr = buffer.add(offset as usize);
+                let model: i64 = *(model_ptr as *const i64);
+
+                let cmd_fn_ptr_ptr = buffer.add(8) as *const i64;
+                let cmd_fn_ptr = (*cmd_fn_ptr_ptr) as *const u8;
+                let cmd_closure_data_ptr = buffer.add(16);
+
+                let msg = run_fx(cmd_fn_ptr, cmd_closure_data_ptr);
+
+                (model, msg)
+            }
+
+            Err(e) => panic!("failed with {}", e),
+        }
+    })
+}
+
+#[no_mangle]
+pub fn rust_main() -> isize {
+    let start_time = SystemTime::now();
+
+    let size = unsafe { roc_main_size() } as usize;
+    let layout = Layout::array::<u8>(size).unwrap();
+    let answer = unsafe {
+        let buffer = std::alloc::alloc(layout);
+
+        roc_main(buffer);
+
+        let output = &*(buffer as *mut RocCallResult<(*const u8, *const u8)>);
+
+        match output.into() {
+            Ok((init_fn_ptr, update_fn_ptr)) => {
+                // let closure_data_ptr = buffer.offset(16);
+                let closure_data_ptr = 0 as *const u8;
+
+                let (mut model, mut msg) =
+                    run_init(init_fn_ptr as *const u8, closure_data_ptr as *const u8);
+
+                for _ in 0..5 {
+                    let result = run_update(
+                        msg,
+                        model,
+                        update_fn_ptr as *const u8,
+                        closure_data_ptr as *const u8,
+                    );
+
+                    model = result.0;
+                    msg = result.1;
+                }
+
+                std::alloc::dealloc(buffer, layout);
+
+                model
+            }
+            Err(msg) => {
+                std::alloc::dealloc(buffer, layout);
+
+                panic!("Roc failed with message: {}", msg);
+            }
+        }
+    };
+    let end_time = SystemTime::now();
+    let duration = end_time.duration_since(start_time).unwrap();
+
+    println!(
+        "Roc closure took {:.4} ms to compute this answer: {:?}",
+        duration.as_secs_f64() * 1000.0,
+        // truncate the answer, so stdout is not swamped
+        answer
+    );
+
+    // Exit code
+    0
+}
+
+/*
+#[no_mangle]
+pub fn old_rust_main() -> isize {
+    println!("Running Roc closure");
+    let start_time = SystemTime::now();
+
+    let size = unsafe { roc_main_size() } as usize;
+    let layout = Layout::array::<u8>(size).unwrap();
+    let answer = unsafe {
+        let buffer = std::alloc::alloc(layout);
+
+        roc_main(buffer);
+
+        let output = &*(buffer as *mut RocCallResult<()>);
+
+        match output.into() {
+            Ok(()) => {
+                let function_pointer = {
+                    // this is a pointer to the location where the function pointer is stored
+                    // we pass just the function pointer
+                    let temp = buffer.offset(8) as *const i64;
+
+                    (*temp) as *const u8
+                };
+
+                let closure_data_ptr = buffer.offset(16);
+
+                let result =
+                    call_the_closure(function_pointer as *const u8, closure_data_ptr as *const u8);
+
+                std::alloc::dealloc(buffer, layout);
+
+                result
+            }
+            Err(msg) => {
+                std::alloc::dealloc(buffer, layout);
+
+                panic!("Roc failed with message: {}", msg);
+            }
+        }
+    };
+    let end_time = SystemTime::now();
+    let duration = end_time.duration_since(start_time).unwrap();
+
+    println!(
+        "Roc closure took {:.4} ms to compute this answer: {:?}",
+        duration.as_secs_f64() * 1000.0,
+        // truncate the answer, so stdout is not swamped
+        answer
+    );
+
+    // Exit code
+    0
+}
+*/