Implements sum for Foldable types

Foldable take a TypeConstructor. The first argument must be a
NatNum.

TODO.md

@@ -12,6 +12,7 @@
 - Also, check the codes for FIXME and TODO
 - Allocation is done using pointers for members, is this desired?
 - See if we want to replace Fractional with Real, and add Rational, Irrationl, Algebraic, Transendental
+  - Implement q32? q64? Two i32/i64 divided?
 - Does Subscript do what we want? It's a language feature rather a normal typed thing. How would you implement your own Subscript-able type?
   - Clean up Subscript implementation - it's half implemented in the compiler. Makes more sense to move more parts to stdlib_types.
 - Have a set of rules or guidelines for the constraint comments, they're messy.

phasm/compiler.py

@@ -2,7 +2,7 @@
 This module contains the code to convert parsed Ourlang into WebAssembly code
 """
 import struct
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Union
 
 from . import codestyle, ourlang, prelude, wasm
 from .runtime import calculate_alloc_size, calculate_member_offset
@@ -292,7 +292,7 @@ def expression(wgn: WasmGenerator, inp: ourlang.Expression) -> None:
         expression(wgn, inp.left)
         expression(wgn, inp.right)
 
-        type_var_map: Dict[type3functions.TypeVariable, type3types.Type3] = {}
+        type_var_map: Dict[Union[type3functions.TypeVariable, type3functions.TypeConstructorVariable], type3types.Type3] = {}
 
         for type_var, arg_expr in zip(inp.operator.signature.args, [inp.left, inp.right, inp], strict=True):
             if not isinstance(type_var, type3functions.TypeVariable):
@@ -315,12 +315,16 @@ def expression(wgn: WasmGenerator, inp: ourlang.Expression) -> None:
             type_var_map = {}
 
             for type_var, arg_expr in zip(inp.function.signature.args, inp.arguments + [inp], strict=True):
-                if not isinstance(type_var, type3functions.TypeVariable):
+                if isinstance(type_var, type3types.Type3):
                     # Fixed type, not part of the lookup requirements
                     continue
 
-                assert arg_expr.type3 is not None, TYPE3_ASSERTION_ERROR
+                if isinstance(type_var, (type3functions.TypeVariable, type3functions.TypeConstructorVariable, )):
-                type_var_map[type_var] = arg_expr.type3
+                    assert arg_expr.type3 is not None, TYPE3_ASSERTION_ERROR
+                    type_var_map[type_var] = arg_expr.type3
+                    continue
+
+                raise NotImplementedError
 
             router = prelude.PRELUDE_TYPE_CLASS_INSTANCE_METHODS[inp.function]
             try:
@@ -720,6 +724,7 @@ def module(inp: ourlang.Module) -> wasm.Module:
         stdlib_types.__u32_pow2__,
         stdlib_types.__u8_rotl__,
         stdlib_types.__u8_rotr__,
+        stdlib_types.__sa_i32_sum__,
     ] + [
         function(x)
         for x in inp.functions.values()

phasm/prelude/__init__.py

@@ -1,25 +1,30 @@
 """
 The prelude are all the builtin types, type classes and methods
 """
-from typing import Callable
+from typing import Any, Callable
 from warnings import warn
 
 from phasm.stdlib import types as stdtypes
 from phasm.wasmgenerator import Generator
 
-from ..type3.functions import TypeVariable
+from ..type3.functions import (
+    Constraint_TypeClassInstanceExists,
+    TypeConstructorVariable,
+    TypeVariable,
+)
 from ..type3.routers import FunctionSignatureRouter
 from ..type3.typeclasses import Type3Class, Type3ClassMethod
 from ..type3.types import (
     IntType3,
     Type3,
     TypeApplication_Nullary,
+    TypeConstructor_Base,
     TypeConstructor_StaticArray,
     TypeConstructor_Struct,
     TypeConstructor_Tuple,
 )
 
-PRELUDE_TYPE_CLASS_INSTANCES_EXISTING: set[tuple[Type3Class, tuple[Type3, ...]]] = set()
+PRELUDE_TYPE_CLASS_INSTANCES_EXISTING: set[tuple[Type3Class, tuple[Type3 | TypeConstructor_Base[Any], ...]]] = set()
 
 PRELUDE_TYPE_CLASS_INSTANCE_METHODS: dict[Type3ClassMethod, FunctionSignatureRouter[Generator, None]] = {}
 
@@ -198,8 +203,9 @@ PRELUDE_TYPES: dict[str, Type3] = {
 a = TypeVariable('a')
 b = TypeVariable('b')
 
+t = TypeConstructorVariable('t')
 
-InternalPassAsPointer = Type3Class('InternalPassAsPointer', [a], methods={}, operators={})
+InternalPassAsPointer = Type3Class('InternalPassAsPointer', (a, ), methods={}, operators={})
 """
 Internal type class to keep track which types we pass arounds as a pointer.
 """
@@ -209,7 +215,7 @@ instance_type_class(InternalPassAsPointer, bytes_)
 # instance_type_class(InternalPassAsPointer, tuple_)
 # instance_type_class(InternalPassAsPointer, struct)
 
-Eq = Type3Class('Eq', [a], methods={}, operators={
+Eq = Type3Class('Eq', (a, ), methods={}, operators={
     '==': [a, a, bool_],
     '!=': [a, a, bool_],
     # FIXME: Do we want to expose 'eqz'? Or is that a compiler optimization?
@@ -248,7 +254,7 @@ instance_type_class(Eq, f64, operators={
     '!=': stdtypes.f64_eq_not_equals,
 })
 
-Ord = Type3Class('Ord', [a], methods={
+Ord = Type3Class('Ord', (a, ), methods={
     'min': [a, a, a],
     'max': [a, a, a],
 }, operators={
@@ -331,7 +337,7 @@ instance_type_class(Ord, f64, methods={
     '>=': stdtypes.f64_ord_greater_than_or_equal,
 })
 
-Bits = Type3Class('Bits', [a], methods={
+Bits = Type3Class('Bits', (a, ), methods={
     'shl': [a, u32, a], # Logical shift left
     'shr': [a, u32, a], # Logical shift right
     'rotl': [a, u32, a], # Rotate bits left
@@ -374,7 +380,7 @@ instance_type_class(Bits, u64, methods={
     '^': stdtypes.u64_bits_bitwise_xor,
 })
 
-NatNum = Type3Class('NatNum', [a], methods={}, operators={
+NatNum = Type3Class('NatNum', (a, ), methods={}, operators={
     '+': [a, a, a],
     '-': [a, a, a],
     '*': [a, a, a],
@@ -425,7 +431,7 @@ instance_type_class(NatNum, f64, operators={
     '>>': stdtypes.f64_natnum_arithmic_shift_right,
 })
 
-IntNum = Type3Class('IntNum', [a], methods={
+IntNum = Type3Class('IntNum', (a, ), methods={
     'abs': [a, a],
     'neg': [a, a],
 }, operators={}, inherited_classes=[NatNum])
@@ -447,7 +453,7 @@ instance_type_class(IntNum, f64, methods={
     'neg': stdtypes.f64_intnum_neg,
 })
 
-Integral = Type3Class('Eq', [a], methods={
+Integral = Type3Class('Eq', (a, ), methods={
 }, operators={
     '//': [a, a, a],
     '%': [a, a, a],
@@ -470,7 +476,7 @@ instance_type_class(Integral, i64, operators={
     '%': stdtypes.i64_integral_rem,
 })
 
-Fractional = Type3Class('Fractional', [a], methods={
+Fractional = Type3Class('Fractional', (a, ), methods={
     'ceil': [a, a],
     'floor': [a, a],
     'trunc': [a, a],
@@ -496,7 +502,7 @@ instance_type_class(Fractional, f64, methods={
     '/': stdtypes.f64_fractional_div,
 })
 
-Floating = Type3Class('Floating', [a], methods={
+Floating = Type3Class('Floating', (a, ), methods={
     'sqrt': [a, a],
 }, operators={}, inherited_classes=[Fractional])
 
@@ -509,7 +515,7 @@ instance_type_class(Floating, f64, methods={
     'sqrt': stdtypes.f64_floating_sqrt,
 })
 
-Sized_ = Type3Class('Sized', [a], methods={
+Sized_ = Type3Class('Sized', (a, ), methods={
     'len': [a, u32],
 }, operators={})  # FIXME: Once we get type class families, add [] here
 
@@ -517,7 +523,7 @@ instance_type_class(Sized_, bytes_, methods={
     'len': stdtypes.bytes_sized_len,
 })
 
-Extendable = Type3Class('Extendable', [a, b], methods={
+Extendable = Type3Class('Extendable', (a, b, ), methods={
     'extend': [a, b],
     'wrap': [b, a],
 }, operators={})
@@ -547,7 +553,7 @@ instance_type_class(Extendable, i32, i64, methods={
     'wrap': stdtypes.i32_i64_wrap,
 })
 
-Promotable = Type3Class('Promotable', [a, b], methods={
+Promotable = Type3Class('Promotable', (a, b, ), methods={
     'promote': [a, b],
     'demote': [b, a],
 }, operators={})
@@ -557,6 +563,16 @@ instance_type_class(Promotable, f32, f64, methods={
     'demote': stdtypes.f32_f64_demote,
 })
 
+Foldable = Type3Class('Foldable', (t, ), methods={
+    'sum': [t(a), a],
+}, operators={}, additional_context={
+    'sum': [Constraint_TypeClassInstanceExists(NatNum, (a, ))],
+})
+
+instance_type_class(Foldable, static_array, methods={
+    'sum': stdtypes.static_array_i32_4_sum,
+})
+
 PRELUDE_TYPE_CLASSES = {
     'Eq': Eq,
     'Ord': Ord,
@@ -592,4 +608,5 @@ PRELUDE_METHODS = {
     **Sized_.methods,
     **Extendable.methods,
     **Promotable.methods,
+    **Foldable.methods,
 }

phasm/stdlib/types.py

@@ -384,6 +384,50 @@ def __u8_rotr__(g: Generator, x: i32, r: i32) -> i32:
 
     return i32('return') # To satisfy mypy
 
+@func_wrapper()
+def __sa_i32_sum__(g: Generator, adr: i32, arlen: i32) -> i32:
+    i32_size = 4
+
+    s = i32('s')
+    stop = i32('stop')
+
+    # stop = adr + ar_len * i32_size
+    g.local.get(adr)
+    g.local.get(arlen)
+    g.i32.const(i32_size)
+    g.i32.mul()
+    g.i32.add()
+    g.local.set(stop)
+
+    # sum = 0
+    g.i32.const(0)
+    g.local.set(s)
+
+    with g.loop():
+        # sum = sum + *adr
+        g.local.get(adr)
+        g.i32.load()
+        g.local.get(s)
+        g.i32.add()
+        g.local.set(s)
+
+        # adr = adr + i32_size
+        g.local.get(adr)
+        g.i32.const(i32_size)
+        g.i32.add()
+        g.local.tee(adr)
+
+        # loop if adr < stop
+        g.local.get(stop)
+        g.i32.lt_u()
+        g.br_if(0)
+
+    # return sum
+    g.local.get(s)
+    g.return_()
+
+    return i32('return') # To satisfy mypy
+
 ## ###
 ## class Eq
 
@@ -920,3 +964,11 @@ def f32_f64_promote(g: Generator) -> None:
 
 def f32_f64_demote(g: Generator) -> None:
     g.f32.demote_f64()
+
+def static_array_i32_4_sum(g: Generator) -> None:
+    g.i32.const(4)
+    g.add_statement('call $stdlib.types.__sa_i32_sum__')
+
+def static_array_i32_5_sum(g: Generator) -> None:
+    g.i32.const(5)
+    g.add_statement('call $stdlib.types.__sa_i32_sum__')

phasm/type3/constraints.py

@@ -3,7 +3,7 @@ This module contains possible constraints generated based on the AST
 
 These need to be resolved before the program can be compiled.
 """
-from typing import Dict, Iterable, List, Optional, Tuple, Union
+from typing import Any, Dict, Iterable, List, Optional, Tuple, Union
 
 from .. import ourlang, prelude
 from . import placeholders, typeclasses, types
@@ -50,7 +50,7 @@ class Context:
     __slots__ = ('type_class_instances_existing', )
 
     # Constraint_TypeClassInstanceExists
-    type_class_instances_existing: set[tuple[typeclasses.Type3Class, tuple[types.Type3, ...]]]
+    type_class_instances_existing: set[tuple[typeclasses.Type3Class, tuple[Union[types.Type3, types.TypeConstructor_Base[Any], types.TypeConstructor_Struct], ...]]]
 
     def __init__(self) -> None:
         self.type_class_instances_existing = set()
@@ -229,7 +229,7 @@ class MustImplementTypeClassConstraint(ConstraintBase):
         self.types = types
 
     def check(self) -> CheckResult:
-        typ_list = []
+        typ_list: list[types.Type3 | types.TypeConstructor_Base[Any] | types.TypeConstructor_Struct] = []
         for typ in self.types:
             if isinstance(typ, placeholders.PlaceholderForType) and typ.resolve_as is not None:
                 typ = typ.resolve_as
@@ -237,7 +237,15 @@ class MustImplementTypeClassConstraint(ConstraintBase):
             if isinstance(typ, placeholders.PlaceholderForType):
                 return RequireTypeSubstitutes()
 
-            typ_list.append(typ)
+            if isinstance(typ.application, (types.TypeApplication_Nullary, types.TypeApplication_Struct, )):
+                typ_list.append(typ)
+                continue
+
+            if isinstance(typ.application, (types.TypeApplication_TypeInt, types.TypeApplication_TypeStar)):
+                typ_list.append(typ.application.constructor)
+                continue
+
+            raise NotImplementedError(typ, typ.application)
 
         assert len(typ_list) == len(self.types)
 

phasm/type3/constraintsgenerator.py

@@ -39,6 +39,88 @@ def constant(ctx: Context, inp: ourlang.Constant, phft: placeholders.Placeholder
 
     raise NotImplementedError(constant, inp)
 
+def expression_binary_op(ctx: Context, inp: ourlang.BinaryOp, phft: PlaceholderForType) -> ConstraintGenerator:
+    return _expression_function_call(
+        ctx,
+        f'({inp.operator.name})',
+        inp.operator.signature,
+        [inp.left, inp.right],
+        inp,
+        phft,
+    )
+
+def expression_function_call(ctx: Context, inp: ourlang.FunctionCall, phft: PlaceholderForType) -> ConstraintGenerator:
+    return _expression_function_call(
+            ctx,
+            inp.function.name,
+            inp.function.signature,
+            inp.arguments,
+            inp,
+            phft,
+        )
+
+def _expression_function_call(
+        ctx: Context,
+        func_name: str,
+        signature: functions.FunctionSignature,
+        arguments: list[ourlang.Expression],
+        return_expr: ourlang.Expression,
+        return_phft: PlaceholderForType,
+    ) -> ConstraintGenerator:
+    """
+    Generates all type-level constraints for a function call.
+
+    A Binary operator functions pretty much the same as a function call
+    with two arguments - it's only a syntactic difference.
+    """
+    arg_placeholders = {
+        arg_expr: PlaceholderForType([arg_expr])
+        for arg_expr in arguments
+    }
+    arg_placeholders[return_expr] = return_phft
+
+    for call_arg in arguments:
+        yield from expression(ctx, call_arg, arg_placeholders[call_arg])
+
+    type_var_map = {
+        x: placeholders.PlaceholderForType([])
+        for x in signature.args
+        if isinstance(x, functions.TypeVariable)
+    }
+
+    print('type_var_map', type_var_map)
+
+    for arg_expr in arguments:
+        yield from expression(ctx, arg_expr, arg_placeholders[arg_expr])
+
+    for constraint in signature.context.constraints:
+        if isinstance(constraint, functions.Constraint_TypeClassInstanceExists):
+            yield MustImplementTypeClassConstraint(
+                ctx,
+                constraint.type_class3,
+                [type_var_map[x] for x in constraint.types],
+            )
+            continue
+
+        raise NotImplementedError(constraint)
+
+    for arg_no, (sig_part, arg_expr) in enumerate(zip(signature.args, arguments + [return_expr], strict=True)):
+        if arg_no == len(arguments):
+            comment = f'The type of a function call to {func_name} is the same as the type that the function returns'
+        else:
+            comment = f'The type of the value passed to argument {arg_no} of function {func_name} should match the type of that argument'
+
+        if isinstance(sig_part, functions.TypeVariable):
+            yield SameTypeConstraint(type_var_map[sig_part], arg_placeholders[arg_expr], comment=comment)
+            continue
+
+        if isinstance(sig_part, type3types.Type3):
+            yield SameTypeConstraint(sig_part, arg_placeholders[arg_expr], comment=comment)
+            continue
+
+        raise NotImplementedError(sig_part)
+    return
+
 def expression(ctx: Context, inp: ourlang.Expression, phft: placeholders.PlaceholderForType) -> ConstraintGenerator:
     if isinstance(inp, ourlang.Constant):
         yield from constant(ctx, inp, phft)
@@ -49,53 +131,12 @@ def expression(ctx: Context, inp: ourlang.Expression, phft: placeholders.Placeho
             comment=f'typeOf("{inp.variable.name}") == typeOf({inp.variable.name})')
         return
 
-    if isinstance(inp, ourlang.BinaryOp) or isinstance(inp, ourlang.FunctionCall):
+    if isinstance(inp, ourlang.BinaryOp):
-        signature = inp.operator.signature if isinstance(inp, ourlang.BinaryOp) else inp.function.signature
+        yield from expression_binary_op(ctx, inp, phft)
-        arguments = [inp.left, inp.right] if isinstance(inp, ourlang.BinaryOp) else inp.arguments
+        return
 
-        func_name = f'({inp.operator.name})' if isinstance(inp, ourlang.BinaryOp) else inp.function.name
+    if isinstance(inp, ourlang.FunctionCall):
-
+        yield from expression_function_call(ctx, inp, phft)
-        type_var_map = {
-            x: placeholders.PlaceholderForType([])
-            for x in signature.args
-            if isinstance(x, functions.TypeVariable)
-        }
-
-        arg_placeholders = {
-            arg_expr: PlaceholderForType([arg_expr])
-            for arg_expr in arguments
-        }
-        arg_placeholders[inp] = phft
-
-        for arg_expr in arguments:
-            yield from expression(ctx, arg_expr, arg_placeholders[arg_expr])
-
-        for constraint in signature.context.constraints:
-            if isinstance(constraint, functions.Constraint_TypeClassInstanceExists):
-                yield MustImplementTypeClassConstraint(
-                    ctx,
-                    constraint.type_class3,
-                    [type_var_map[x] for x in constraint.types],
-                )
-                continue
-
-            raise NotImplementedError(constraint)
-
-        for arg_no, (sig_part, arg_expr) in enumerate(zip(signature.args, arguments + [inp], strict=True)):
-            if arg_no == len(arguments):
-                comment = f'The type of a function call to {func_name} is the same as the type that the function returns'
-            else:
-                comment = f'The type of the value passed to argument {arg_no} of function {func_name} should match the type of that argument'
-
-            if isinstance(sig_part, functions.TypeVariable):
-                yield SameTypeConstraint(type_var_map[sig_part], arg_placeholders[arg_expr], comment=comment)
-                continue
-
-            if isinstance(sig_part, type3types.Type3):
-                yield SameTypeConstraint(sig_part, arg_placeholders[arg_expr], comment=comment)
-                continue
-
-            raise NotImplementedError(sig_part)
         return
 
     if isinstance(inp, ourlang.TupleInstantiation):

phasm/type3/functions.py

@@ -19,9 +19,18 @@ class TypeVariable:
     letter: str
 
     def __init__(self, letter: str) -> None:
-        assert len(letter) == 1, f'{letter} is not a valid type variable'
         self.letter = letter
 
+    def deconstruct(self) -> 'TypeConstructorVariable | None':
+        letter_list = self.letter.split(' ')
+        if len(letter_list) == 1:
+            return None
+
+        if len(letter_list) == 2:
+            return TypeConstructorVariable(letter_list[0])
+
+        raise NotImplementedError(letter_list)
+
     def __hash__(self) -> int:
         return hash(self.letter)
 
@@ -34,6 +43,38 @@ class TypeVariable:
     def __repr__(self) -> str:
         return f'TypeVariable({repr(self.letter)})'
 
+class TypeConstructorVariable:
+    """
+    Types constructor variable are used in function definition.
+
+    They are a lot like TypeVariable, except that they represent a
+    type constructor rather than a type directly.
+
+    For now, we only have type constructor variables for kind
+    * -> *.
+    """
+    __slots__ = ('letter', )
+
+    letter: str
+
+    def __init__(self, letter: str) -> None:
+        self.letter = letter
+
+    def __hash__(self) -> int:
+        return hash((self.letter, ))
+
+    def __eq__(self, other: Any) -> bool:
+        if not isinstance(other, TypeConstructorVariable):
+            raise NotImplementedError
+
+        return (self.letter == other.letter)
+
+    def __call__(self, tvar: TypeVariable) -> 'TypeVariable':
+        return TypeVariable(self.letter + ' ' + tvar.letter)
+
+    def __repr__(self) -> str:
+        return f'TypeConstructorVariable({self.letter!r})'
+
 class ConstraintBase:
     __slots__ = ()
 
@@ -62,13 +103,11 @@ class TypeVariableContext:
 
     constraints: list[ConstraintBase]
 
-    def __init__(self) -> None:
+    def __init__(self, constraints: Iterable[ConstraintBase] = ()) -> None:
-        self.constraints = []
+        self.constraints = list(constraints)
 
     def __copy__(self) -> 'TypeVariableContext':
-        result = TypeVariableContext()
+        return TypeVariableContext(self.constraints)
-        result.constraints.extend(self.constraints)
-        return result
 
     def __str__(self) -> str:
         if not self.constraints:

phasm/type3/typeclasses.py

@@ -2,7 +2,9 @@ from typing import Dict, Iterable, List, Mapping, Optional, Union
 
 from .functions import (
     Constraint_TypeClassInstanceExists,
+    ConstraintBase,
     FunctionSignature,
+    TypeConstructorVariable,
     TypeVariable,
     TypeVariableContext,
 )
@@ -29,7 +31,7 @@ class Type3Class:
     __slots__ = ('name', 'args', 'methods', 'operators', 'inherited_classes', )
 
     name: str
-    args: List[TypeVariable]
+    args: tuple[TypeVariable] | tuple[TypeVariable, TypeVariable] | tuple[TypeConstructorVariable]
     methods: Dict[str, Type3ClassMethod]
     operators: Dict[str, Type3ClassMethod]
     inherited_classes: List['Type3Class']
@@ -37,26 +39,60 @@ class Type3Class:
     def __init__(
             self,
             name: str,
-            args: Iterable[TypeVariable],
+            args: tuple[TypeVariable] | tuple[TypeVariable, TypeVariable] | tuple[TypeConstructorVariable],
             methods: Mapping[str, Iterable[Union[Type3, TypeVariable]]],
             operators: Mapping[str, Iterable[Union[Type3, TypeVariable]]],
             inherited_classes: Optional[List['Type3Class']] = None,
+            additional_context: Optional[Mapping[str, Iterable[ConstraintBase]]] = None,
         ) -> None:
         self.name = name
-        self.args = list(args)
+        self.args = args
-
-        context = TypeVariableContext()
-        context.constraints.append(Constraint_TypeClassInstanceExists(self, args))
 
         self.methods = {
-            k: Type3ClassMethod(k, FunctionSignature(context, v))
+            k: Type3ClassMethod(k, _create_signature(v, self))
             for k, v in methods.items()
         }
         self.operators = {
-            k: Type3ClassMethod(k, FunctionSignature(context, v))
+            k: Type3ClassMethod(k, _create_signature(v, self))
             for k, v in operators.items()
         }
         self.inherited_classes = inherited_classes or []
 
+        if additional_context:
+            for func_name, constraint_list in additional_context.items():
+                func = self.methods.get(func_name) or self.operators.get(func_name)
+                assert func is not None  # type hint
+
+                func.signature.context.constraints.extend(constraint_list)
+
     def __repr__(self) -> str:
         return self.name
+
+def _create_signature(
+        method_arg_list: Iterable[Type3 | TypeVariable],
+        type_class3: Type3Class,
+    ) -> FunctionSignature:
+    context = TypeVariableContext()
+    if not isinstance(type_class3.args[0], TypeConstructorVariable):
+        context.constraints.append(Constraint_TypeClassInstanceExists(type_class3, type_class3.args))
+
+    signature_args: list[Type3 | TypeVariable] = []
+    for method_arg in method_arg_list:
+        if isinstance(method_arg, Type3):
+            signature_args.append(method_arg)
+            continue
+
+        if isinstance(method_arg, TypeVariable):
+            type_constructor = method_arg.deconstruct()
+            if type_constructor is None:
+                signature_args.append(method_arg)
+                continue
+
+            if (type_constructor, ) == type_class3.args:
+                context.constraints.append(Constraint_TypeClassInstanceExists(type_class3, [method_arg]))
+                signature_args.append(method_arg)
+                continue
+
+        raise NotImplementedError(method_arg)
+
+    return FunctionSignature(context, signature_args)

tests/integration/test_lang/test_foldable.py

@@ -0,0 +1,55 @@
+import pytest
+
+from phasm.type3.entry import Type3Exception
+
+from ..helpers import Suite
+
+
+@pytest.mark.integration_test
+def test_foldable_sum():
+    code_py = """
+@exported
+def testEntry(x: i32[5]) -> i32:
+    return sum(x)
+"""
+
+    result = Suite(code_py).run_code((4, 5, 6, 7, 8, ))
+
+    assert 30 == result.returned_value
+
+@pytest.mark.integration_test
+def test_foldable_sum_not_natnum():
+    code_py = """
+class Foo:
+    bar: i32
+
+@exported
+def testEntry(x: Foo[4]) -> Foo:
+    return sum(x)
+"""
+
+    with pytest.raises(Type3Exception, match='Missing type class instantation: NatNum Foo'):
+        Suite(code_py).run_code()
+
+
+@pytest.mark.integration_test
+def test_foldable_invalid_return_type():
+    code_py = """
+@exported
+def testEntry(x: i32[5]) -> f64:
+    return sum(x)
+"""
+
+    with pytest.raises(Type3Exception, match='f64 must be i32 instead'):
+        Suite(code_py).run_code((4, 5, 6, 7, 8, ))
+
+@pytest.mark.integration_test
+def test_foldable_not_foldable():
+    code_py = """
+@exported
+def testEntry(x: i32) -> i32:
+    return sum(x)
+"""
+
+    with pytest.raises(Type3Exception, match='Missing type class instantation: Foldable i32'):
+        Suite(code_py).run_code()