diff --git a/py2wasm/python.py b/py2wasm/python.py
index 853fd25..9710051 100644
--- a/py2wasm/python.py
+++ b/py2wasm/python.py
@@ -2,7 +2,7 @@
 Code for parsing the source (python-alike) code
 """
 
-from typing import List, Optional, Union, Tuple
+from typing import Dict, Generator, List, Optional, Union, Tuple
 
 import ast
 
@@ -10,6 +10,10 @@ from . import wasm
 
 # pylint: disable=C0103,R0201
 
+StatementGenerator = Generator[wasm.Statement, None, None]
+
+WLocals = Dict[str, str]
+
 class Visitor:
     """
     Class to visit a Python syntax tree
@@ -27,7 +31,7 @@ class Visitor:
 
         for stmt in node.body:
             if isinstance(stmt, ast.FunctionDef):
-                wnode = self.visit_FunctionDef(stmt)
+                wnode = self.visit_FunctionDef(module, stmt)
 
                 if isinstance(wnode, wasm.Import):
                     module.imports.append(wnode)
@@ -39,13 +43,18 @@ class Visitor:
 
         return module
 
-    def visit_FunctionDef(self, node: ast.FunctionDef) -> Union[wasm.Import, wasm.Function]:
+    def visit_FunctionDef(
+            self,
+            module: wasm.Module,
+            node: ast.FunctionDef,
+        ) -> Union[wasm.Import, wasm.Function]:
         """
         A Python function definition with the @external decorator is returned as import.
 
         Other functions are returned as (exported) functions.
-        """
 
+        Nested / dynamicly created functions are not yet supported
+        """
         exported = False
 
         if node.decorator_list:
@@ -68,40 +77,197 @@ class Visitor:
 
                 assert not call.keywords
 
-                module, name, intname = _parse_import_decorator(node.name, call.args)
+                mod, name, intname = _parse_import_decorator(node.name, call.args)
 
-                return wasm.Import(module, name, intname, _parse_import_args(node.args))
+                return wasm.Import(mod, name, intname, _parse_import_args(node.args))
+            else:
+                raise NotImplementedError
 
-        result = _parse_annotation(node.returns)
+        result = None if node.returns is None else _parse_annotation(node.returns)
 
-        statements = [
-            self.visit_stmt(node, stmt)
-            for stmt in node.body
+        assert not node.args.vararg
+        assert not node.args.kwonlyargs
+        assert not node.args.kw_defaults
+        assert not node.args.kwarg
+        assert not node.args.defaults
+
+        params = [
+            (a.arg, _parse_annotation(a.annotation), )
+            for a in [
+                *node.args.posonlyargs,
+                *node.args.args,
+            ]
         ]
 
-        return wasm.Function(node.name, exported, result, statements)
+        wlocals: WLocals = dict(params)
 
-    def visit_stmt(self, func: ast.FunctionDef, stmt: ast.stmt) -> wasm.Statement:
+        statements: List[wasm.Statement] = []
+        for py_stmt in node.body:
+            statements.extend(
+                self.visit_stmt(module, node, wlocals, py_stmt)
+            )
+
+        return wasm.Function(node.name, exported, params, result, statements)
+
+    def visit_stmt(
+            self,
+            module: wasm.Module,
+            func: ast.FunctionDef,
+            wlocals: WLocals,
+            stmt: ast.stmt,
+        ) -> StatementGenerator:
         """
-        Visits a statement node
+        Visits a statement node within a function
         """
         if isinstance(stmt, ast.Return):
-            return self.visit_Return(func, stmt)
+            return self.visit_Return(module, func, wlocals, stmt)
 
-        raise NotImplementedError
+        if isinstance(stmt, ast.Expr):
+            assert isinstance(stmt.value, ast.Call)
 
-    def visit_Return(self, func: ast.FunctionDef, stmt: ast.Return) -> wasm.Statement:
+            return self.visit_Call(module, wlocals, "None", stmt.value)
+
+        raise NotImplementedError(stmt)
+
+    def visit_Return(
+            self,
+            module: wasm.Module,
+            func: ast.FunctionDef,
+            wlocals: WLocals,
+            stmt: ast.Return,
+        ) -> StatementGenerator:
         """
         Visits a statement node
         """
-        assert isinstance(stmt.value, ast.Constant)
-        assert isinstance(stmt.value.value, int)
+
+        assert stmt.value is not None
 
         return_type = _parse_annotation(func.returns)
 
-        return wasm.Statement(
-            '{}.const'.format(return_type),
-            str(stmt.value.value)
+        return self.visit_expr(module, wlocals, return_type, stmt.value)
+
+    def visit_expr(
+            self,
+            module: wasm.Module,
+            wlocals: WLocals,
+            exp_type: str,
+            node: ast.expr,
+        ) -> StatementGenerator:
+        """
+        Visit an expression node
+        """
+        if isinstance(node, ast.BinOp):
+            return self.visit_BinOp(module, wlocals, exp_type, node)
+
+        if isinstance(node, ast.Call):
+            return self.visit_Call(module, wlocals, exp_type, node)
+
+        if isinstance(node, ast.Constant):
+            return self.visit_Constant(exp_type, node)
+
+        if isinstance(node, ast.Name):
+            return self.visit_Name(wlocals, exp_type, node)
+
+        raise NotImplementedError(node)
+
+    def visit_BinOp(
+            self,
+            module: wasm.Module,
+            wlocals: WLocals,
+            exp_type: str,
+            node: ast.BinOp,
+        ) -> StatementGenerator:
+        """
+        Visits a BinOp node as (part of) an expression
+        """
+        yield from self.visit_expr(module, wlocals, exp_type, node.left)
+        yield from self.visit_expr(module, wlocals, exp_type, node.right)
+
+        if isinstance(node.op, ast.Add):
+            yield wasm.Statement('{}.add'.format(exp_type))
+            return
+
+        raise NotImplementedError(node.op)
+
+    def visit_Call(
+            self,
+            module: wasm.Module,
+            wlocals: WLocals,
+            exp_type: str,
+            node: ast.Call,
+        ) -> StatementGenerator:
+        """
+        Visits a Call node as (part of) an expression
+        """
+        assert isinstance(node.func, ast.Name)
+        assert not node.keywords
+
+        called_name = node.func.id
+
+        called_func_list = [
+            x
+            for x in module.functions
+            if x.name == called_name
+        ]
+        if called_func_list:
+            assert len(called_func_list) == 1
+            called_params = called_func_list[0].params
+            called_result = called_func_list[0].result
+        else:
+            called_import_list = [
+                x
+                for x in module.imports
+                if x.name == node.func.id
+            ]
+            if called_import_list:
+                assert len(called_import_list) == 1
+                called_params = called_import_list[0].params
+                called_result = called_import_list[0].result
+            else:
+                assert 1 == len(called_func_list), \
+                    'Could not find function {}'.format(node.func.id)
+
+        assert exp_type == called_result
+
+        assert len(called_params) == len(node.args), \
+            '{}:{} Function {} requires {} arguments, but {} are supplied'.format(
+                node.lineno, node.col_offset,
+                called_name, len(called_params), len(node.args),
+            )
+
+        for (_, exp_expr_type), expr in zip(called_params, node.args):
+            yield from self.visit_expr(module, wlocals, exp_expr_type, expr)
+
+        yield wasm.Statement(
+            'call',
+            '${}'.format(called_name),
+        )
+
+    def visit_Constant(self, exp_type: str, node: ast.Constant) -> StatementGenerator:
+        """
+        Visits a Constant node as (part of) an expression
+        """
+        if 'i32' == exp_type:
+            assert isinstance(node.value, int)
+            assert -2147483648 <= node.value <= 2147483647
+
+            yield wasm.Statement(
+                '{}.const'.format(exp_type),
+                str(node.value)
+            )
+            return
+
+        raise NotImplementedError(exp_type)
+
+    def visit_Name(self, wlocals: WLocals, exp_type: str, node: ast.Name) -> StatementGenerator:
+        """
+        Visits a Name node as (part of) an expression
+        """
+        assert node.id in wlocals
+        assert exp_type == wlocals[node.id]
+        yield wasm.Statement(
+            'local.get',
+            '${}'.format(node.id),
         )
 
 def _parse_import_decorator(func_name: str, args: List[ast.expr]) -> Tuple[str, str, str]:
@@ -156,99 +322,3 @@ def _parse_annotation(ann: Optional[ast.expr]) -> str:
     result = ann.id
     assert result in ['i32']
     return result
-
-
-
-
-    # def visit_ImportFrom(self, node):
-    #     for alias in node.names:
-    #         self.imports.append(Import(
-    #             node.module,
-    #             alias.name,
-    #             alias.asname,
-    #         ))
-    #
-    # def generic_visit(self, node: Any) -> None:
-    #     print(node)
-    #     super().generic_visit(node)
-    #
-    # def visit_FunctionDef(self, node: ast.FunctionDef) -> None:
-    #     is_export = False
-    #
-    #     if node.decorator_list:
-    #         assert 1 == len(node.decorator_list)
-    #
-    #         call = node.decorator_list[0]
-    #         if not isinstance(call, ast.Name):
-    #             assert isinstance(call, ast.Call)
-    #
-    #             assert 'external' == call.func.id
-    #             assert 1 == len(call.args)
-    #             assert isinstance(call.args[0].value, str)
-    #
-    #             import_ = Import(
-    #                 call.args[0].value,
-    #                 node.name,
-    #                 node.name,
-    #             )
-    #
-    #             import_.params = [
-    #                 arg.annotation.id
-    #                 for arg in node.args.args
-    #             ]
-    #
-    #             self.module.imports.append(import_)
-    #             return
-    #
-    #         assert call.id == 'export'
-    #         is_export = True
-    #
-    #     func = Function(
-    #         node.name,
-    #         is_export,
-    #     )
-    #
-    #     for arg in node.args.args:
-    #         func.params.append(
-    #             (arg.arg, arg.annotation.id)
-    #         )
-    #     func.result = node.returns
-    #
-    #     self._stack.append(func)
-    #     self.generic_visit(node)
-    #     self._stack.pop()
-    #
-    #     self.module.functions.append(func)
-    #
-    # def visit_Call(self, node: ast.Call) -> None:
-    #     self.generic_visit(node)
-    #
-    #     func = self._stack[-1]
-    #     func.statements.append(
-    #         Statement('call', '$' + node.func.id)
-    #     )
-    #
-    # def visit_BinOp(self, node: ast.BinOp) -> None:
-    #     self.generic_visit(node)
-    #
-    #     func = self._stack[-1]
-    #
-    #     if 'Add' == node.op.__class__.__name__:
-    #         func.statements.append(
-    #             Statement('i32.add')
-    #         )
-    #     elif 'Mult' == node.op.__class__.__name__:
-    #         func.statements.append(
-    #             Statement('i32.mul')
-    #         )
-    #     else:
-    #         raise NotImplementedError
-    #
-    # def visit_Constant(self, node: ast.Constant) -> None:
-    #     func = self._stack[-1]
-    #     if isinstance(node.value, int):
-    #         func.statements.append(
-    #             Statement('i32.const', str(node.value))
-    #         )
-    #
-    #     self.generic_visit(node)
diff --git a/py2wasm/wasm.py b/py2wasm/wasm.py
index fd1b43a..24d1f46 100644
--- a/py2wasm/wasm.py
+++ b/py2wasm/wasm.py
@@ -4,6 +4,8 @@ Python classes for storing the representation of Web Assembly code
 
 from typing import Iterable, List, Optional, Tuple
 
+Param = Tuple[str, str]
+
 class Import:
     """
     Represents a Web Assembly import
@@ -13,12 +15,13 @@ class Import:
             module: str,
             name: str,
             intname: str,
-            params: Iterable[Tuple[str, str]],
+            params: Iterable[Param],
         ) -> None:
         self.module = module
         self.name = name
         self.intname = intname
         self.params = [*params]
+        self.result: str = 'None'
 
     def generate(self) -> str:
         """
@@ -53,12 +56,13 @@ class Function:
             self,
             name: str,
             exported: bool,
+            params: Iterable[Param],
             result: Optional[str],
             statements: Iterable[Statement],
         ) -> None:
         self.name = name
         self.exported = exported
-        self.params: List[Tuple[str, str]] = []
+        self.params = [*params]
         self.result = result
         self.statements = [*statements]
 
diff --git a/pylintrc b/pylintrc
index 72d74db..eb6abcb 100644
--- a/pylintrc
+++ b/pylintrc
@@ -1,2 +1,2 @@
 [MASTER]
-disable=C0122,R0903
+disable=C0122,R0903,R0913
diff --git a/tests/integration/test_fib.py b/tests/integration/test_fib.py
index fa1eaf9..ff00b05 100644
--- a/tests/integration/test_fib.py
+++ b/tests/integration/test_fib.py
@@ -2,19 +2,26 @@ from .helpers import Suite
 
 def test_fib():
     code_py = """
-@imported('console')
-def logInt32(value: i32) -> None:
-    ...
+def helper(n: i32, a: i32, b: i32) -> i32:
+    if n < 1:
+        return a + b
 
-def helper(value: i32) -> i32:
-    return value + 1
+    return helper(n - 1, a + b, a)
+
+def fib(n: i32) -> i32:
+    if n == 0:
+        return 0
+
+    if n == 1:
+        return 1
+
+    return helper(n - 1, 0, 1)
 
 @exported
 def testEntry():
-    logInt32(13 + 13 * helper(122))
+    return fib(40)
 """
 
     result = Suite(code_py, 'test_fib').run_code()
 
-    assert None is result.returned_value
-    assert [1612] == result.log_int32_list
+    assert 102334155 == result.returned_value
diff --git a/tests/integration/test_simple.py b/tests/integration/test_simple.py
index 99ce3ce..0d015b4 100644
--- a/tests/integration/test_simple.py
+++ b/tests/integration/test_simple.py
@@ -9,5 +9,32 @@ def testEntry() -> i32:
 
     result = Suite(code_py, 'test_fib').run_code()
 
-    assert 13 is result.returned_value
+    assert 13 == result.returned_value
+    assert [] == result.log_int32_list
+
+def test_addition():
+    code_py = """
+@exported
+def testEntry() -> i32:
+    return 10 + 3
+"""
+
+    result = Suite(code_py, 'test_fib').run_code()
+
+    assert 13 == result.returned_value
+    assert [] == result.log_int32_list
+
+def test_call():
+    code_py = """
+def helper(left: i32, right: i32) -> i32:
+    return left + right
+
+@exported
+def testEntry() -> i32:
+    return helper(10, 3)
+"""
+
+    result = Suite(code_py, 'test_fib').run_code()
+
+    assert 13 == result.returned_value
     assert [] == result.log_int32_list