diff --git a/phasm/build/base.py b/phasm/build/base.py
index f8d3687..fb49486 100644
--- a/phasm/build/base.py
+++ b/phasm/build/base.py
@@ -16,7 +16,7 @@ from ..type3.routers import (
     TypeClassArgsRouter,
     TypeVariableLookup,
 )
-from ..type3.typeclasses import Type3Class, Type3ClassMethod
+from ..typeclass import TypeClass
 from ..type3.types import (
     IntType3,
     Type3,
@@ -33,6 +33,7 @@ from ..type5 import typeexpr as type5typeexpr
 from ..wasm import WasmType, WasmTypeInt32, WasmTypeNone
 from . import builtins
 from .typerouter import TypeAllocSize, TypeName
+from .typevariablerouter import TypeVariableRouter
 
 TypeInfo = NamedTuple('TypeInfo', [
     # Name of the type
@@ -179,27 +180,27 @@ class BuildBase[G]:
     Types that are available without explicit import.
     """
 
-    type_classes: dict[str, Type3Class]
+    type_classes: dict[str, TypeClass]
     """
     Type classes that are available without explicit import.
     """
 
-    type_class_instances: set[tuple[Type3Class, tuple[Type3 | TypeConstructor_Base[Any], ...]]]
+    type_class_instances: dict[str, set[tuple[type5typeexpr.TypeExpr, ...]]]
     """
     Type class instances that are available without explicit import.
     """
 
-    type_class_instance_methods: dict[Type3ClassMethod, TypeClassArgsRouter[G, None]]
+    # type_class_instance_methods: dict[tuple[TypeClass, str], TypeClassArgsRouter[G, None]]
     """
     Methods (and operators) for type class instances that are available without explicit import.
     """
 
-    methods: dict[str, Type3ClassMethod]
+    methods: dict[str, tuple[type5typeexpr.TypeExpr, TypeVariableRouter[G]]]
     """
     Methods that are available without explicit import.
     """
 
-    operators: dict[str, Type3ClassMethod]
+    # operators: dict[str, Type3ClassMethod]
     """
     Operators that are available without explicit import.
     """
@@ -268,7 +269,7 @@ class BuildBase[G]:
             'u32': self.u32_type5,
         }
         self.type_classes = {}
-        self.type_class_instances = set()
+        self.type_class_instances = {}
         self.type_class_instance_methods = {}
         self.methods = {}
         self.operators = {}
@@ -282,83 +283,112 @@ class BuildBase[G]:
         self.type5_alloc_size_root = TypeAllocSize(self, is_member=False)
         self.type5_alloc_size_member = TypeAllocSize(self, is_member=True)
 
-    def register_type_class(self, cls: Type3Class) -> None:
-        """
-        Register that the given type class exists
-        """
-        old_len_methods = len(self.methods)
-        old_len_operators = len(self.operators)
+    # def register_type_class(self, cls: Type3Class) -> None:
+    #     """
+    #     Register that the given type class exists
+    #     """
+        # old_len_methods = len(self.methods)
+        # old_len_operators = len(self.operators)
+
+        # self.type_classes[cls.name] = cls
+        # self.methods.update(cls.methods)
+        # self.operators.update(cls.operators)
+
+        # assert len(self.methods) == old_len_methods + len(cls.methods), 'Duplicated method detected'
+        # assert len(self.operators) == old_len_operators + len(cls.operators), 'Duplicated operator detected'
+
+    # def instance_type_class(
+    #     self,
+    #     cls: Type3Class,
+    #     *typ: Type3 | TypeConstructor_Base[Any],
+    #     methods: dict[str, Callable[[G, TypeVariableLookup], None]] = {},
+    #     operators: dict[str, Callable[[G, TypeVariableLookup], None]] = {},
+    # ) -> None:
+    #     """
+    #     Registered the given type class and its implementation
+    #     """
+    #     assert len(cls.args) == len(typ)
+
+    #     for incls in cls.inherited_classes:
+    #         if (incls, tuple(typ), ) not in self.type_class_instances:
+    #             warn(MissingImplementationWarning(
+    #                 incls.name + ' ' + ' '.join(x.name for x in typ) + ' - required for ' + cls.name
+    #             ))
+
+    #     # First just register the type
+    #     self.type_class_instances.add((cls, tuple(typ), ))
+
+    #     # Then make the implementation findable
+    #     # We route based on the type class arguments.
+    #     tv_map: dict[TypeVariable, Type3] = {}
+    #     tc_map: dict[TypeConstructorVariable, TypeConstructor_Base[Any]] = {}
+    #     for arg_tv, arg_tp in zip(cls.args, typ, strict=True):
+    #         if isinstance(arg_tv, TypeVariable):
+    #             assert isinstance(arg_tp, Type3)
+    #             tv_map[arg_tv] = arg_tp
+    #         elif isinstance(arg_tv, TypeConstructorVariable):
+    #             assert isinstance(arg_tp, TypeConstructor_Base)
+    #             tc_map[arg_tv] = arg_tp
+    #         else:
+    #             raise NotImplementedError(arg_tv, arg_tp)
+
+    #     for method_name, method in cls.methods.items():
+    #         router = self.type_class_instance_methods.get(method)
+    #         if router is None:
+    #             router = TypeClassArgsRouter[G, None](cls.args)
+    #             self.type_class_instance_methods[method] = router
+
+    #         try:
+    #             generator = methods[method_name]
+    #         except KeyError:
+    #             warn(MissingImplementationWarning(str(method), cls.name + ' ' + ' '.join(x.name for x in typ)))
+    #             continue
+
+    #         router.add(tv_map, tc_map, generator)
+
+    #     for operator_name, operator in cls.operators.items():
+    #         router = self.type_class_instance_methods.get(operator)
+    #         if router is None:
+    #             router = TypeClassArgsRouter[G, None](cls.args)
+    #             self.type_class_instance_methods[operator] = router
+
+    #         try:
+    #             generator = operators[operator_name]
+    #         except KeyError:
+    #             warn(MissingImplementationWarning(str(operator), cls.name + ' ' + ' '.join(x.name for x in typ)))
+    #             continue
+
+    #         router.add(tv_map, tc_map, generator)
+
+    def register_type_class(self, cls: TypeClass) -> None:
+        assert cls.name not in self.type_classes, 'Duplicate typeclass name'
 
         self.type_classes[cls.name] = cls
-        self.methods.update(cls.methods)
-        self.operators.update(cls.operators)
+        self.type_class_instances[cls.name] = set()
 
-        assert len(self.methods) == old_len_methods + len(cls.methods), 'Duplicated method detected'
-        assert len(self.operators) == old_len_operators + len(cls.operators), 'Duplicated operator detected'
+    def register_type_class_method(
+            self,
+            cls: TypeClass,
+            name: str,
+            type: type5typeexpr.TypeExpr,
+        ) -> None:
+        assert name not in self.methods, 'Duplicate typeclass method name'
 
-    def instance_type_class(
-        self,
-        cls: Type3Class,
-        *typ: Type3 | TypeConstructor_Base[Any],
-        methods: dict[str, Callable[[G, TypeVariableLookup], None]] = {},
-        operators: dict[str, Callable[[G, TypeVariableLookup], None]] = {},
-    ) -> None:
-        """
-        Registered the given type class and its implementation
-        """
-        assert len(cls.args) == len(typ)
+        self.methods[name] = (type, TypeVariableRouter(), )
 
-        for incls in cls.inherited_classes:
-            if (incls, tuple(typ), ) not in self.type_class_instances:
-                warn(MissingImplementationWarning(
-                    incls.name + ' ' + ' '.join(x.name for x in typ) + ' - required for ' + cls.name
-                ))
+    def register_type_class_instance(
+            self,
+            cls: TypeClass,
+            *args: type5typeexpr.TypeExpr,
+            methods: dict[str, Callable[[G, Any], None]],
+        ) -> None:
+        self.type_class_instances[cls.name].add(tuple(args))
 
-        # First just register the type
-        self.type_class_instances.add((cls, tuple(typ), ))
-
-        # Then make the implementation findable
-        # We route based on the type class arguments.
-        tv_map: dict[TypeVariable, Type3] = {}
-        tc_map: dict[TypeConstructorVariable, TypeConstructor_Base[Any]] = {}
-        for arg_tv, arg_tp in zip(cls.args, typ, strict=True):
-            if isinstance(arg_tv, TypeVariable):
-                assert isinstance(arg_tp, Type3)
-                tv_map[arg_tv] = arg_tp
-            elif isinstance(arg_tv, TypeConstructorVariable):
-                assert isinstance(arg_tp, TypeConstructor_Base)
-                tc_map[arg_tv] = arg_tp
-            else:
-                raise NotImplementedError(arg_tv, arg_tp)
-
-        for method_name, method in cls.methods.items():
-            router = self.type_class_instance_methods.get(method)
-            if router is None:
-                router = TypeClassArgsRouter[G, None](cls.args)
-                self.type_class_instance_methods[method] = router
-
-            try:
-                generator = methods[method_name]
-            except KeyError:
-                warn(MissingImplementationWarning(str(method), cls.name + ' ' + ' '.join(x.name for x in typ)))
-                continue
-
-            router.add(tv_map, tc_map, generator)
-
-        for operator_name, operator in cls.operators.items():
-            router = self.type_class_instance_methods.get(operator)
-            if router is None:
-                router = TypeClassArgsRouter[G, None](cls.args)
-                self.type_class_instance_methods[operator] = router
-
-            try:
-                generator = operators[operator_name]
-            except KeyError:
-                warn(MissingImplementationWarning(str(operator), cls.name + ' ' + ' '.join(x.name for x in typ)))
-                continue
-
-            router.add(tv_map, tc_map, generator)
+        assert len(cls.variables) == len(args)
 
+        for mtd_nam, mtd_imp in methods.items():
+            _, mtd_rtr = self.methods[mtd_nam]
+            mtd_rtr.register(cls.variables, args, mtd_imp)
 
     def calculate_alloc_size_static_array(self, args: tuple[Type3, IntType3]) -> int:
         """
diff --git a/phasm/build/default.py b/phasm/build/default.py
index c072457..6a5cc70 100644
--- a/phasm/build/default.py
+++ b/phasm/build/default.py
@@ -98,14 +98,15 @@ class BuildDefault(BuildBase[Generator]):
         })
 
         tc_list = [
-            bits,
-            eq, ord,
-            extendable, promotable,
-            convertable, reinterpretable,
-            natnum, intnum, fractional, floating,
-                            integral,
-            foldable, subscriptable,
-            sized,
+            floating,
+            # bits,
+            # eq, ord,
+            # extendable, promotable,
+            # convertable, reinterpretable,
+            # natnum, intnum, fractional, floating,
+            #                 integral,
+            # foldable, subscriptable,
+            # sized,
         ]
 
         for tc in tc_list:
diff --git a/phasm/build/typeclasses/floating.py b/phasm/build/typeclasses/floating.py
index dc838e8..10ce0ac 100644
--- a/phasm/build/typeclasses/floating.py
+++ b/phasm/build/typeclasses/floating.py
@@ -3,24 +3,30 @@ The Floating type class is defined for Real numbers.
 """
 from typing import Any
 
-from ...type3.functions import make_typevar
+from ...type5.kindexpr import Star
+from ...type5.typeexpr import TypeVariable
 from ...type3.routers import TypeVariableLookup
-from ...type3.typeclasses import Type3Class
+from ...typeclass import TypeClass
 from ...wasmgenerator import Generator as WasmGenerator
 from ..base import BuildBase
 
 
 def load(build: BuildBase[Any]) -> None:
-    a = make_typevar('a')
-    Fractional = build.type_classes['Fractional']
-
-    Floating = Type3Class('Floating', (a, ), methods={
-        'sqrt': [a, a],
-    }, operators={}, inherited_classes=[Fractional])
-    # FIXME: Do we want to expose copysign?
+    a = TypeVariable(kind=Star(), name='a')
 
+    Floating = TypeClass('Floating', [a])
     build.register_type_class(Floating)
 
+    build.register_type_class_method(Floating, 'sqrt', build.type5_make_function([a, a]))
+
+    # a = make_typevar('a')
+    # # Fractional = build.type_classes['Fractional']  # TODO
+
+    # Floating = Type3Class('Floating', (a, ), methods={
+    #     'sqrt': [a, a],
+    # }, operators={}, inherited_classes=[Fractional])
+    # # FIXME: Do we want to expose copysign?
+
 def wasm_f32_sqrt(g: WasmGenerator, tv_map: TypeVariableLookup) -> None:
     del tv_map
     g.add_statement('f32.sqrt')
@@ -32,9 +38,9 @@ def wasm_f64_sqrt(g: WasmGenerator, tv_map: TypeVariableLookup) -> None:
 def wasm(build: BuildBase[WasmGenerator]) -> None:
     Floating = build.type_classes['Floating']
 
-    build.instance_type_class(Floating, build.types['f32'], methods={
+    build.register_type_class_instance(Floating, build.type5s['f32'], methods={
         'sqrt': wasm_f32_sqrt,
     })
-    build.instance_type_class(Floating, build.types['f64'], methods={
+    build.register_type_class_instance(Floating, build.type5s['f64'], methods={
         'sqrt': wasm_f64_sqrt,
     })
diff --git a/phasm/build/typevariablerouter.py b/phasm/build/typevariablerouter.py
new file mode 100644
index 0000000..3f65ffd
--- /dev/null
+++ b/phasm/build/typevariablerouter.py
@@ -0,0 +1,39 @@
+from typing import Any, Callable, Iterable, TypeAlias
+
+from ..type5 import typeexpr as type5typeexpr
+
+class TypeVariableRouter[G]:
+	__slots__ = ('data', )
+
+	data: dict[
+		tuple[tuple[type5typeexpr.TypeVariable, type5typeexpr.TypeExpr], ...],
+		Callable[[G, dict[type5typeexpr.TypeVariable, type5typeexpr.TypeExpr]], None],
+	]
+
+	def __init__(self) -> None:
+		self.data = {}
+
+	def register(
+			self,
+			variables: Iterable[type5typeexpr.TypeVariable],
+			types: Iterable[type5typeexpr.TypeExpr],
+			implementation: Callable[[G, Any], None],
+		) -> None:
+		variables = list(variables)
+		types = list(types)
+
+		assert len(variables) == len(set(variables))
+
+		key = tuple(sorted(tuple(zip(variables, types))))
+		self.data[key] = implementation
+
+	def __call__(
+			self,
+			variables: Iterable[type5typeexpr.TypeVariable],
+			types: Iterable[type5typeexpr.TypeExpr],
+		) -> Callable[[G, Any], None]:
+		variables = list(variables)
+		types = list(types)
+
+		key = tuple(sorted(tuple(zip(variables, types))))
+		return self.data[key]
diff --git a/phasm/codestyle.py b/phasm/codestyle.py
index fc0f8ef..965b345 100644
--- a/phasm/codestyle.py
+++ b/phasm/codestyle.py
@@ -6,7 +6,6 @@ It's intented to be a "any color, as long as it's black" kind of renderer
 from typing import Any, Generator
 
 from . import ourlang
-from .type3.types import Type3, TypeApplication_Struct
 from .type5 import typeexpr as type5typeexpr
 
 
@@ -18,35 +17,27 @@ def phasm_render(inp: ourlang.Module[Any]) -> str:
 
 Statements = Generator[str, None, None]
 
-def type3(inp: Type3) -> str:
-    """
-    Render: type's name
-    """
-    return inp.name
-
 def type5(mod: ourlang.Module[Any], inp: type5typeexpr.TypeExpr) -> str:
     """
     Render: type's name
     """
     return mod.build.type5_name(inp)
 
-def struct_definition(inp: ourlang.StructDefinition) -> str:
+def struct_definition(mod: ourlang.Module[Any], inp: ourlang.StructDefinition) -> str:
     """
     Render: TypeStruct's definition
     """
-    assert isinstance(inp.struct_type3.application, TypeApplication_Struct)
-
-    result = f'class {inp.struct_type3.name}:\n'
-    for mem, typ in inp.struct_type3.application.arguments:
-        result += f'    {mem}: {type3(typ)}\n'
+    result = f'class {inp.struct_type5.name}:\n'
+    for mem, typ in inp.struct_type5.fields:
+        result += f'    {mem}: {type5(mod, typ)}\n'
 
     return result
 
-def constant_definition(inp: ourlang.ModuleConstantDef) -> str:
+def constant_definition(mod: ourlang.Module[Any], inp: ourlang.ModuleConstantDef) -> str:
     """
     Render: Module Constant's  definition
     """
-    return f'{inp.name}: {type3(inp.type3)} = {expression(inp.constant)}\n'
+    return f'{inp.name}: {type5(mod, inp.type5)} = {expression(inp.constant)}\n'
 
 def expression(inp: ourlang.Expression) -> str:
     """
@@ -67,7 +58,7 @@ def expression(inp: ourlang.Expression) -> str:
         ) + ', )'
 
     if isinstance(inp, ourlang.ConstantStruct):
-        return inp.struct_type3.name + '(' + ', '.join(
+        return inp.struct_type5.name + '(' + ', '.join(
             expression(x)
             for x in inp.value
         ) + ')'
@@ -76,7 +67,7 @@ def expression(inp: ourlang.Expression) -> str:
         return str(inp.variable.name)
 
     if isinstance(inp, ourlang.BinaryOp):
-        return f'{expression(inp.left)} {inp.operator.name} {expression(inp.right)}'
+        return f'{expression(inp.left)} {inp.operator.function.name} {expression(inp.right)}'
 
     if isinstance(inp, ourlang.FunctionCall):
         args = ', '.join(
@@ -84,10 +75,10 @@ def expression(inp: ourlang.Expression) -> str:
             for arg in inp.arguments
         )
 
-        if isinstance(inp.function, ourlang.StructConstructor):
-            return f'{inp.function.struct_type3.name}({args})'
+        if isinstance(inp.function_instance.function, ourlang.StructConstructor):
+            return f'{inp.function_instance.function.struct_type5.name}({args})'
 
-        return f'{inp.function.name}({args})'
+        return f'{inp.function_instance.function.name}({args})'
 
     if isinstance(inp, ourlang.FunctionReference):
         return str(inp.function.name)
@@ -148,12 +139,17 @@ def function(mod: ourlang.Module[Any], inp: ourlang.Function) -> str:
     if inp.imported:
         result += '@imported\n'
 
+    assert inp.type5 is not None
+    fn_args = mod.build.type5_is_function(inp.type5)
+    assert fn_args is not None
+    ret_type5 = fn_args.pop()
+
     args = ', '.join(
-        f'{p.name}: {type5(mod, p.type5)}'
-        for p in inp.posonlyargs
+        f'{arg_name}: {type5(mod, arg_type)}'
+        for arg_name, arg_type in zip(inp.arg_names, fn_args, strict=True)
     )
 
-    result += f'def {inp.name}({args}) -> {type3(inp.returns_type3)}:\n'
+    result += f'def {inp.name}({args}) -> {type5(mod, ret_type5)}:\n'
 
     if inp.imported:
         result += '    pass\n'
@@ -174,12 +170,12 @@ def module(inp: ourlang.Module[Any]) -> str:
     for struct in inp.struct_definitions.values():
         if result:
             result += '\n'
-        result += struct_definition(struct)
+        result += struct_definition(inp, struct)
 
     for cdef in inp.constant_defs.values():
         if result:
             result += '\n'
-        result += constant_definition(cdef)
+        result += constant_definition(inp, cdef)
 
     for func in inp.functions.values():
         if isinstance(func, ourlang.StructConstructor):
diff --git a/phasm/compiler.py b/phasm/compiler.py
index 394c9e8..2b0b50b 100644
--- a/phasm/compiler.py
+++ b/phasm/compiler.py
@@ -15,10 +15,9 @@ from .type3.routers import NoRouteForTypeException
 from .type3.typeclasses import Type3ClassMethod
 from .type3.types import (
     Type3,
-    TypeApplication_Struct,
-    TypeConstructor_Function,
 )
 from .type5.typeexpr import TypeExpr, is_concrete
+from .type5.unify import ActionList, ReplaceVariable, unify
 from .wasm import (
     WasmTypeFloat32,
     WasmTypeFloat64,
@@ -156,6 +155,48 @@ def expression_subscript_tuple(wgn: WasmGenerator, mod: ourlang.Module[WasmGener
     expression(wgn, mod, inp.varref)
     wgn.add_statement(el_type_info.wasm_load_func, f'offset={offset}')
 
+def expression_function_call(wgn: WasmGenerator, mod: ourlang.Module[WasmGenerator], inp: ourlang.FunctionCall) -> None:
+    for arg in inp.arguments:
+        expression(wgn, mod, arg)
+
+    if isinstance(inp.function_instance.function, ourlang.BuiltinFunction):
+        assert _is_concrete(inp.function_instance.type5), TYPE5_ASSERTION_ERROR
+
+        method_type, method_router = mod.build.methods[inp.function_instance.function.name]
+        instance_type = inp.function_instance.type5
+
+        actions = unify(method_type, instance_type)
+        assert isinstance(actions, ActionList)
+
+        tv_map = {}
+        for action in actions:
+            if isinstance(action, ReplaceVariable):
+                tv_map[action.var] = action.typ
+                continue
+            raise NotImplementedError
+
+        method_router(tv_map.keys(), tv_map.values())(wgn, None)
+        return
+
+    if isinstance(inp.function_instance.function, ourlang.FunctionParam):
+        assert _is_concrete(inp.function_instance.type5), TYPE5_ASSERTION_ERROR
+
+        fn_args = mod.build.type5_is_function(inp.function_instance.type5)
+        assert fn_args is not None
+
+        params = [
+            type5(mod, x)
+            for x in fn_args
+        ]
+
+        result = params.pop()
+
+        wgn.add_statement('local.get', '${}'.format(inp.function_instance.function.name))
+        wgn.call_indirect(params=params, result=result)
+        return
+
+    wgn.call(inp.function_instance.function.name)
+
 def expression(wgn: WasmGenerator, mod: ourlang.Module[WasmGenerator], inp: ourlang.Expression) -> None:
     """
     Compile: Any expression
@@ -217,80 +258,11 @@ def expression(wgn: WasmGenerator, mod: ourlang.Module[WasmGenerator], inp: ourl
         raise NotImplementedError(expression, inp.variable)
 
     if isinstance(inp, ourlang.BinaryOp):
-        expression(wgn, mod, inp.left)
-        expression(wgn, mod, inp.right)
-
-        type_var_map: dict[TypeVariable, Type3] = {}
-
-        for type_var, arg_expr in zip(inp.operator.signature.args, [inp.left, inp.right, inp], strict=True):
-            assert arg_expr.type3 is not None, TYPE3_ASSERTION_ERROR
-
-            if isinstance(type_var, Type3):
-                # Fixed type, not part of the lookup requirements
-                continue
-
-            if isinstance(type_var, TypeVariable):
-                type_var_map[type_var] = arg_expr.type3
-                continue
-
-            if isinstance(type_var, FunctionArgument):
-                # Fixed type, not part of the lookup requirements
-                continue
-
-            raise NotImplementedError(type_var, arg_expr.type3)
-
-        router = mod.build.type_class_instance_methods[inp.operator]
-        router(wgn, type_var_map)
+        expression_binary_op(wgn, mod, inp)
         return
 
     if isinstance(inp, ourlang.FunctionCall):
-        for arg in inp.arguments:
-            expression(wgn, mod, arg)
-
-        if isinstance(inp.function, Type3ClassMethod):
-            # FIXME: Duplicate code with BinaryOp
-            type_var_map = {}
-
-            for type_var, arg_expr in zip(inp.function.signature.args, inp.arguments + [inp], strict=True):
-                assert arg_expr.type3 is not None, TYPE3_ASSERTION_ERROR
-
-                if isinstance(type_var, Type3):
-                    # Fixed type, not part of the lookup requirements
-                    continue
-
-                if isinstance(type_var, TypeVariable):
-                    type_var_map[type_var] = arg_expr.type3
-                    continue
-
-                if isinstance(type_var, FunctionArgument):
-                    # Fixed type, not part of the lookup requirements
-                    continue
-
-                raise NotImplementedError(type_var, arg_expr.type3)
-
-            router = mod.build.type_class_instance_methods[inp.function]
-            try:
-                router(wgn, type_var_map)
-            except NoRouteForTypeException:
-                raise NotImplementedError(str(inp.function), type_var_map)
-            return
-
-        if isinstance(inp.function, ourlang.FunctionParam):
-            fn_args = mod.build.type5_is_function(inp.function.type5)
-            assert fn_args is not None
-
-            params = [
-                type5(mod, x)
-                for x in fn_args
-            ]
-
-            result = params.pop()
-
-            wgn.add_statement('local.get', '${}'.format(inp.function.name))
-            wgn.call_indirect(params=params, result=result)
-            return
-
-        wgn.call(inp.function.name)
+        expression_function_call(wgn, mod, inp)
         return
 
     if isinstance(inp, ourlang.FunctionReference):
@@ -314,6 +286,8 @@ def expression(wgn: WasmGenerator, mod: ourlang.Module[WasmGenerator], inp: ourl
             expression_subscript_tuple(wgn, mod, inp)
             return
 
+        raise NotImplementedError
+
         inp_as_fc = ourlang.FunctionCall(mod.build.type_classes['Subscriptable'].operators['[]'], inp.sourceref)
         inp_as_fc.type3 = inp.type3
         inp_as_fc.type5 = inp.type5
@@ -349,11 +323,11 @@ def statement_return(wgn: WasmGenerator, mod: ourlang.Module[WasmGenerator], fun
     # Support tail calls
     # https://github.com/WebAssembly/tail-call
     # These help a lot with some functional programming techniques
-    if isinstance(inp.value, ourlang.FunctionCall) and inp.value.function is fun:
+    if isinstance(inp.value, ourlang.FunctionCall) and inp.value.function_instance.function is fun:
         for arg in inp.value.arguments:
             expression(wgn, mod, arg)
 
-        wgn.add_statement('return_call', '${}'.format(inp.value.function.name))
+        wgn.add_statement('return_call', '${}'.format(inp.value.function_instance.function.name))
         return
 
     expression(wgn, mod, inp.value)
diff --git a/phasm/ourlang.py b/phasm/ourlang.py
index ebe8445..c75549e 100644
--- a/phasm/ourlang.py
+++ b/phasm/ourlang.py
@@ -1,11 +1,12 @@
 """
 Contains the syntax tree for ourlang
 """
+from __future__ import annotations
+
 from typing import Dict, Iterable, List, Optional, Union
 
 from .build.base import BuildBase
 from .type3.functions import FunctionSignature, TypeVariableContext
-from .type3.typeclasses import Type3ClassMethod
 from .type3.types import Type3, TypeApplication_Struct
 from .type5 import record as type5record
 from .type5 import typeexpr as type5typeexpr
@@ -164,11 +165,11 @@ class BinaryOp(Expression):
     """
     __slots__ = ('operator', 'left', 'right', )
 
-    operator: Type3ClassMethod
+    operator: FunctionInstance
     left: Expression
     right: Expression
 
-    def __init__(self, operator: Type3ClassMethod, left: Expression, right: Expression, sourceref: SourceRef) -> None:
+    def __init__(self, operator: FunctionInstance, left: Expression, right: Expression, sourceref: SourceRef) -> None:
         super().__init__(sourceref=sourceref)
 
         self.operator = operator
@@ -178,19 +179,33 @@ class BinaryOp(Expression):
     def __repr__(self) -> str:
         return f'BinaryOp({repr(self.operator)}, {repr(self.left)}, {repr(self.right)})'
 
+class FunctionInstance(Expression):
+    """
+    When calling a polymorphic function with concrete arguments, we can generate
+    code for that specific instance of the function.
+    """
+    __slots__ = ('function', )
+
+    function: Union['Function', 'FunctionParam']
+
+    def __init__(self, function: Union['Function', 'FunctionParam'], sourceref: SourceRef) -> None:
+        super().__init__(sourceref=sourceref)
+
+        self.function = function
+
 class FunctionCall(Expression):
     """
     A function call expression within a statement
     """
-    __slots__ = ('function', 'arguments', )
+    __slots__ = ('function_instance', 'arguments', )
 
-    function: Union['Function', 'FunctionParam', Type3ClassMethod]
+    function_instance: FunctionInstance
     arguments: List[Expression]
 
-    def __init__(self, function: Union['Function', 'FunctionParam', Type3ClassMethod], sourceref: SourceRef) -> None:
+    def __init__(self, function_instance: FunctionInstance, sourceref: SourceRef) -> None:
         super().__init__(sourceref=sourceref)
 
-        self.function = function
+        self.function_instance = function_instance
         self.arguments = []
 
 class FunctionReference(Expression):
@@ -349,6 +364,11 @@ class Function:
         self.posonlyargs = []
         self.arg_names = []
 
+class BuiltinFunction(Function):
+    def __init__(self, name: str, type5: type5typeexpr.TypeExpr) -> None:
+        super().__init__(name, SourceRef("/", 0, 0), None)
+        self.type5 = type5
+
 class StructDefinition:
     """
     The definition for a struct
@@ -453,8 +473,8 @@ class Module[G]:
     struct_definitions: Dict[str, StructDefinition]
     constant_defs: Dict[str, ModuleConstantDef]
     functions: Dict[str, Function]
-    methods: Dict[str, Type3ClassMethod]
-    operators: Dict[str, Type3ClassMethod]
+    methods: Dict[str, type5typeexpr.TypeExpr]
+    operators: Dict[str, type5typeexpr.TypeExpr]
     functions_table: dict[Function, int]
 
     def __init__(self, build: BuildBase[G], filename: str) -> None:
diff --git a/phasm/parser.py b/phasm/parser.py
index 3705c85..65ba53e 100644
--- a/phasm/parser.py
+++ b/phasm/parser.py
@@ -10,6 +10,7 @@ from .exceptions import StaticError
 from .ourlang import (
     AccessStructMember,
     BinaryOp,
+    BuiltinFunction,
     ConstantBytes,
     ConstantPrimitive,
     ConstantStruct,
@@ -17,6 +18,7 @@ from .ourlang import (
     Expression,
     Function,
     FunctionCall,
+    FunctionInstance,
     FunctionParam,
     FunctionReference,
     Module,
@@ -100,7 +102,7 @@ class OurVisitor[G]:
     def visit_Module(self, node: ast.Module) -> Module[G]:
         module = Module(self.build, "-")
 
-        module.methods.update(self.build.methods)
+        module.methods.update({k: v[0] for k, v in self.build.methods.items()})
         module.operators.update(self.build.operators)
         module.types.update(self.build.types)
         module.type5s.update(self.build.type5s)
@@ -415,7 +417,7 @@ class OurVisitor[G]:
                 raise NotImplementedError(f'Operator {operator}')
 
             return BinaryOp(
-                module.operators[operator],
+                FunctionInstance(module.operators[operator], srf(module, node)),
                 self.visit_Module_FunctionDef_expr(module, function, our_locals, node.left),
                 self.visit_Module_FunctionDef_expr(module, function, our_locals, node.right),
                 srf(module, node),
@@ -444,7 +446,7 @@ class OurVisitor[G]:
                 raise NotImplementedError(f'Operator {operator}')
 
             return BinaryOp(
-                module.operators[operator],
+                FunctionInstance(module.operators[operator], srf(module, node)),
                 self.visit_Module_FunctionDef_expr(module, function, our_locals, node.left),
                 self.visit_Module_FunctionDef_expr(module, function, our_locals, node.comparators[0]),
                 srf(module, node),
@@ -512,7 +514,7 @@ class OurVisitor[G]:
         func: Union[Function, FunctionParam, Type3ClassMethod]
 
         if node.func.id in module.methods:
-            func = module.methods[node.func.id]
+            func = BuiltinFunction(node.func.id, module.methods[node.func.id])
         elif node.func.id in our_locals:
             func = our_locals[node.func.id]
         else:
@@ -521,7 +523,7 @@ class OurVisitor[G]:
 
             func = module.functions[node.func.id]
 
-        result = FunctionCall(func, sourceref=srf(module, node))
+        result = FunctionCall(FunctionInstance(func, srf(module, node)), sourceref=srf(module, node))
         result.arguments.extend(
             self.visit_Module_FunctionDef_expr(module, function, our_locals, arg_expr)
             for arg_expr in node.args
diff --git a/phasm/type5/constraints.py b/phasm/type5/constraints.py
index 3d88365..d0f80ca 100644
--- a/phasm/type5/constraints.py
+++ b/phasm/type5/constraints.py
@@ -39,8 +39,8 @@ class Context:
         self.build = build
         self.placeholder_update = {}
 
-    def make_placeholder(self, arg: ExpressionProtocol | None = None, kind: KindExpr = Star()) -> TypeVariable:
-        res = TypeVariable(kind, f"p_{len(self.placeholder_update)}")
+    def make_placeholder(self, arg: ExpressionProtocol | None = None, kind: KindExpr = Star(), prefix: str = 'p') -> TypeVariable:
+        res = TypeVariable(kind, f"{prefix}_{len(self.placeholder_update)}")
         self.placeholder_update[res] = arg
         return res
 
@@ -440,18 +440,9 @@ class TypeClassInstanceExistsConstraint(ConstraintBase):
         if len(c_arg_list) != len(self.arg_list):
             return skip_for_now()
 
-        tcls = self.ctx.build.type_classes[self.typeclass]
-
-        # Temporary hack while we are converting from type3 to type5
-        try:
-            targs = tuple(
-                _type5_to_type3_or_type3_const(self.ctx.build, x)
-                for x in self.arg_list
-            )
-        except RecordFoundException:
-            return fail('Missing type class instance')
-
-        if (tcls, targs, ) in self.ctx.build.type_class_instances:
+        key = tuple(c_arg_list)
+        existing_instances = self.ctx.build.type_class_instances[self.typeclass]
+        if key in existing_instances:
             return ok()
 
         return fail('Missing type class instance')
diff --git a/phasm/type5/fromast.py b/phasm/type5/fromast.py
index 20654ca..8d0d8a4 100644
--- a/phasm/type5/fromast.py
+++ b/phasm/type5/fromast.py
@@ -17,7 +17,7 @@ from .constraints import (
     UnifyTypesConstraint,
 )
 from .kindexpr import Star
-from .typeexpr import TypeApplication, TypeExpr, TypeVariable
+from .typeexpr import TypeApplication, TypeExpr, TypeVariable, instantiate
 
 ConstraintGenerator = Generator[ConstraintBase, None, None]
 
@@ -107,17 +107,15 @@ def expression_function_call(ctx: Context, inp: ourlang.FunctionCall, phft: Type
         yield from expression(ctx, arg, arg_tv)
         arg_typ_list.append(arg_tv)
 
-    if isinstance(inp.function, type3classes.Type3ClassMethod):
-        func_type, constraints = _signature_to_type5(ctx, inp.sourceref, inp.function.signature)
-    else:
-        assert isinstance(inp.function.type5, TypeExpr)
-        func_type = inp.function.type5
-        constraints = []
+    assert isinstance(inp.function_instance.function.type5, TypeExpr)
+    inp.function_instance.type5 = ctx.make_placeholder(inp.function_instance)
+    yield UnifyTypesConstraint(ctx, inp.sourceref, instantiate(inp.function_instance.function.type5, {}, lambda x, p: ctx.make_placeholder(kind=x, prefix=p)), inp.function_instance.type5)
+    # constraints = []
 
     expr_type = ctx.build.type5_make_function(arg_typ_list + [phft])
 
-    yield UnifyTypesConstraint(ctx, inp.sourceref, func_type, expr_type)
-    yield from constraints
+    yield UnifyTypesConstraint(ctx, inp.sourceref, inp.function_instance.type5, expr_type)
+    # yield from constraints
 
 def expression_function_reference(ctx: Context, inp: ourlang.FunctionReference, phft: TypeVariable) -> ConstraintGenerator:
     assert inp.function.type5 is not None  # Todo: Make not nullable
diff --git a/phasm/type5/solver.py b/phasm/type5/solver.py
index 291cc8e..48bcc9b 100644
--- a/phasm/type5/solver.py
+++ b/phasm/type5/solver.py
@@ -3,7 +3,7 @@ from typing import Any
 from ..ourlang import Module
 from .constraints import ConstraintBase, Context
 from .fromast import phasm_type5_generate_constraints
-from .typeexpr import TypeExpr, TypeVariable
+from .typeexpr import TypeExpr, TypeVariable, replace_variable
 from .unify import ReplaceVariable
 
 MAX_RESTACK_COUNT = 10 # 100
@@ -47,10 +47,12 @@ def phasm_type5(inp: Module[Any], verbose: bool = False) -> None:
                 if isinstance(action, ReplaceVariable):
                     action_var: TypeExpr = action.var
                     while isinstance(action_var, TypeVariable) and action_var in placeholder_types:
+                        #  TODO: Does this still happen?
                         action_var = placeholder_types[action_var]
 
                     action_typ: TypeExpr = action.typ
                     while isinstance(action_typ, TypeVariable) and action_typ in placeholder_types:
+                        #  TODO: Does this still happen?
                         action_typ = placeholder_types[action_typ]
 
                     # print(inp.build.type5_name(action_var), ':=', inp.build.type5_name(action_typ))
@@ -62,6 +64,11 @@ def phasm_type5(inp: Module[Any], verbose: bool = False) -> None:
                         action_typ, action_var = action_var, action_typ
 
                     if isinstance(action_var, TypeVariable):
+                        # Ensure all existing found types are updated
+                        placeholder_types = {
+                            k: replace_variable(v, action_var, action_typ)
+                            for k, v in placeholder_types.items()
+                        }
                         placeholder_types[action_var] = action_typ
 
                         for oth_const in new_constraint_list + constraint_list:
diff --git a/phasm/type5/typeexpr.py b/phasm/type5/typeexpr.py
index 3ae8e84..33b24ae 100644
--- a/phasm/type5/typeexpr.py
+++ b/phasm/type5/typeexpr.py
@@ -19,6 +19,9 @@ class AtomicType(TypeExpr):
     def __init__(self, name: str) -> None:
         super().__init__(Star(), name)
 
+    def __hash__(self) -> int:
+        return hash((self.kind, self.name))
+
 @dataclass
 class TypeLevelNat(TypeExpr):
     value: int
@@ -42,8 +45,6 @@ class TypeVariable(TypeExpr):
 
 @dataclass
 class TypeConstructor(TypeExpr):
-    name: str
-
     def __init__(self, kind: Arrow, name: str) -> None:
         super().__init__(kind, name)
 
@@ -145,3 +146,33 @@ def replace_variable(expr: TypeExpr, var: TypeVariable, rep_expr: TypeExpr) -> T
         )
 
     raise NotImplementedError
+
+def instantiate(
+        expr: TypeExpr,
+        known_map: dict[TypeVariable, TypeVariable],
+        make_variable: Callable[[KindExpr, str], TypeVariable],
+    ) -> TypeExpr:
+    if isinstance(expr, AtomicType):
+        return expr
+
+    if isinstance(expr, TypeLevelNat):
+        return expr
+
+    if isinstance(expr, TypeVariable):
+        known_map.setdefault(expr, make_variable(expr.kind, expr.name))
+        return known_map[expr]
+
+    if isinstance(expr, TypeConstructor):
+        return expr
+
+    if isinstance(expr, TypeApplication):
+        new_constructor = instantiate(expr.constructor, known_map, make_variable)
+
+        assert isinstance(new_constructor, TypeConstructor | TypeApplication | TypeVariable)  # type hint
+
+        return TypeApplication(
+            constructor=new_constructor,
+            argument=instantiate(expr.argument, known_map, make_variable),
+        )
+
+    raise NotImplementedError(expr)
diff --git a/phasm/typeclass/__init__.py b/phasm/typeclass/__init__.py
new file mode 100644
index 0000000..53dcae9
--- /dev/null
+++ b/phasm/typeclass/__init__.py
@@ -0,0 +1,8 @@
+from dataclasses import dataclass
+
+from ..type5.typeexpr import TypeVariable
+
+@dataclass
+class TypeClass:
+	name: str
+	variables: list[TypeVariable]
diff --git a/tests/integration/runners.py b/tests/integration/runners.py
index 188627e..c58fdbf 100644
--- a/tests/integration/runners.py
+++ b/tests/integration/runners.py
@@ -41,7 +41,6 @@ class RunnerBase:
         """
         self.phasm_ast = phasm_parse(self.phasm_code)
         phasm_type5(self.phasm_ast, verbose=verbose)
-        phasm_type3(self.phasm_ast, verbose=False)
 
     def compile_ast(self) -> None:
         """