diff --git a/artiq/compiler/__init__.py b/artiq/compiler/__init__.py
index e69de29bb..8f210ac92 100644
--- a/artiq/compiler/__init__.py
+++ b/artiq/compiler/__init__.py
@@ -0,0 +1 @@
+from .module import Module
diff --git a/artiq/compiler/module.py b/artiq/compiler/module.py
new file mode 100644
index 000000000..82b1ef455
--- /dev/null
+++ b/artiq/compiler/module.py
@@ -0,0 +1,33 @@
+"""
+The :class:`Module` class encapsulates a single Python
+"""
+
+import os
+from pythonparser import source, diagnostic, parse_buffer
+from . import prelude, types, transforms
+
+class Module:
+    def __init__(self, source_buffer, engine=diagnostic.Engine(all_errors_are_fatal=True)):
+        parsetree, comments = parse_buffer(source_buffer, engine=engine)
+        self.name = os.path.basename(source_buffer.name)
+
+        asttyped_rewriter = transforms.ASTTypedRewriter(engine=engine)
+        typedtree = asttyped_rewriter.visit(parsetree)
+        self.globals = asttyped_rewriter.globals
+
+        inferencer = transforms.Inferencer(engine=engine)
+        inferencer.visit(typedtree)
+
+    @classmethod
+    def from_string(klass, source_string, name="input.py", first_line=1):
+        return klass(source.Buffer(source_string + "\n", name, first_line))
+
+    @classmethod
+    def from_filename(klass, filename):
+        with open(filename) as f:
+            return klass(source.Buffer(f.read(), filename, 1))
+
+    def __repr__(self):
+        printer = types.TypePrinter()
+        globals = ["%s: %s" % (var, printer.name(self.globals[var])) for var in self.globals]
+        return "<artiq.compiler.Module %s {\n  %s\n}>" % (repr(self.name), ",\n  ".join(globals))
diff --git a/artiq/compiler/testbench/__init__.py b/artiq/compiler/testbench/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/artiq/compiler/testbench/inferencer.py b/artiq/compiler/testbench/inferencer.py
new file mode 100644
index 000000000..b330bf055
--- /dev/null
+++ b/artiq/compiler/testbench/inferencer.py
@@ -0,0 +1,75 @@
+import sys, fileinput, os
+from pythonparser import source, diagnostic, algorithm, parse_buffer
+from .. import prelude, types
+from ..transforms import ASTTypedRewriter, Inferencer
+
+class Printer(algorithm.Visitor):
+    """
+    :class:`Printer` prints ``:`` and the node type after every typed node,
+    and ``->`` and the node type before the colon in a function definition.
+
+    In almost all cases (except function definition) this does not result
+    in valid Python syntax.
+
+    :ivar rewriter: (:class:`pythonparser.source.Rewriter`) rewriter instance
+    """
+
+    def __init__(self, buf):
+        self.rewriter = source.Rewriter(buf)
+        self.type_printer = types.TypePrinter()
+
+    def rewrite(self):
+        return self.rewriter.rewrite()
+
+    def visit_FunctionDefT(self, node):
+        super().generic_visit(node)
+
+        self.rewriter.insert_before(node.colon_loc,
+                                    "->{}".format(self.type_printer.name(node.return_type)))
+
+    def visit_ExceptHandlerT(self, node):
+        super().generic_visit(node)
+
+        if node.name_loc:
+            self.rewriter.insert_after(node.name_loc,
+                                        ":{}".format(self.type_printer.name(node.name_type)))
+
+    def generic_visit(self, node):
+        super().generic_visit(node)
+
+        if hasattr(node, "type"):
+            self.rewriter.insert_after(node.loc,
+                                       ":{}".format(self.type_printer.name(node.type)))
+
+def main():
+    if len(sys.argv) > 1 and sys.argv[1] == '+diag':
+        del sys.argv[1]
+        def process_diagnostic(diag):
+            print("\n".join(diag.render(only_line=True)))
+            if diag.level == 'fatal':
+                exit()
+    else:
+        def process_diagnostic(diag):
+            print("\n".join(diag.render()))
+            if diag.level in ('fatal', 'error'):
+                exit(1)
+
+    engine = diagnostic.Engine()
+    engine.process = process_diagnostic
+
+    buf = source.Buffer("".join(fileinput.input()).expandtabs(),
+                        os.path.basename(fileinput.filename()))
+    parsed, comments = parse_buffer(buf, engine=engine)
+    typed = ASTTypedRewriter(globals=prelude.globals(), engine=engine).visit(parsed)
+    Inferencer(engine=engine).visit(typed)
+
+    printer = Printer(buf)
+    printer.visit(typed)
+    for comment in comments:
+        if comment.text.find("CHECK") >= 0:
+            printer.rewriter.remove(comment.loc)
+    print(printer.rewrite().source)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/artiq/compiler/transforms/__init__.py b/artiq/compiler/transforms/__init__.py
new file mode 100644
index 000000000..749508a5a
--- /dev/null
+++ b/artiq/compiler/transforms/__init__.py
@@ -0,0 +1,2 @@
+from .asttyped_rewriter import ASTTypedRewriter
+from .inferencer import Inferencer
diff --git a/artiq/compiler/transforms/asttyped_rewriter.py b/artiq/compiler/transforms/asttyped_rewriter.py
new file mode 100644
index 000000000..065c05ee0
--- /dev/null
+++ b/artiq/compiler/transforms/asttyped_rewriter.py
@@ -0,0 +1,377 @@
+from pythonparser import algorithm, diagnostic
+from .. import asttyped, types, builtins, prelude
+
+# This visitor will be called for every node with a scope,
+# i.e.: class, function, comprehension, lambda
+class LocalExtractor(algorithm.Visitor):
+    def __init__(self, env_stack, engine):
+        super().__init__()
+        self.env_stack  = env_stack
+        self.engine     = engine
+
+        self.in_root    = False
+        self.in_assign  = False
+        self.typing_env = {}
+
+        # which names are global have to be recorded in the current scope
+        self.global_    = set()
+
+        # which names are nonlocal only affects whether the current scope
+        # gets a new binding or not, so we throw this away
+        self.nonlocal_  = set()
+
+        # parameters can't be declared as global or nonlocal
+        self.params     = set()
+
+    def visit_in_assign(self, node):
+        try:
+            self.in_assign = True
+            return self.visit(node)
+        finally:
+            self.in_assign = False
+
+    def visit_Assign(self, node):
+        self.visit(node.value)
+        for target in node.targets:
+            self.visit_in_assign(target)
+
+    def visit_For(self, node):
+        self.visit(node.iter)
+        self.visit_in_assign(node.target)
+        self.visit(node.body)
+        self.visit(node.orelse)
+
+    def visit_withitem(self, node):
+        self.visit(node.context_expr)
+        if node.optional_vars is not None:
+            self.visit_in_assign(node.optional_vars)
+
+    def visit_comprehension(self, node):
+        self.visit(node.iter)
+        self.visit_in_assign(node.target)
+        for if_ in node.ifs:
+            self.visit(node.ifs)
+
+    def visit_root(self, node):
+        if self.in_root:
+            return
+        self.in_root = True
+        self.generic_visit(node)
+
+    visit_Module       = visit_root # don't look at inner scopes
+    visit_ClassDef     = visit_root
+    visit_Lambda       = visit_root
+    visit_DictComp     = visit_root
+    visit_ListComp     = visit_root
+    visit_SetComp      = visit_root
+    visit_GeneratorExp = visit_root
+
+    def visit_FunctionDef(self, node):
+        if self.in_root:
+            self._assignable(node.name)
+        self.visit_root(node)
+
+    def _assignable(self, name):
+        if name not in self.typing_env and name not in self.nonlocal_:
+            self.typing_env[name] = types.TVar()
+
+    def visit_arg(self, node):
+        if node.arg in self.params:
+            diag = diagnostic.Diagnostic("error",
+                "duplicate parameter '{name}'", {"name": node.arg},
+                node.loc)
+            self.engine.process(diag)
+            return
+        self._assignable(node.arg)
+        self.params.add(node.arg)
+
+    def visit_Name(self, node):
+        if self.in_assign:
+            # code like:
+            # x = 1
+            # def f():
+            #   x = 1
+            # creates a new binding for x in f's scope
+            self._assignable(node.id)
+
+    def _check_not_in(self, name, names, curkind, newkind, loc):
+        if name in names:
+            diag = diagnostic.Diagnostic("error",
+                "name '{name}' cannot be {curkind} and {newkind} simultaneously",
+                {"name": name, "curkind": curkind, "newkind": newkind}, loc)
+            self.engine.process(diag)
+            return True
+        return False
+
+    def visit_Global(self, node):
+        for name, loc in zip(node.names, node.name_locs):
+            if self._check_not_in(name, self.nonlocal_, "nonlocal", "global", loc) or \
+                    self._check_not_in(name, self.params, "a parameter", "global", loc):
+               continue
+
+            self.global_.add(name)
+            self._assignable(name)
+            self.env_stack[1][name] = self.typing_env[name]
+
+    def visit_Nonlocal(self, node):
+        for name, loc in zip(node.names, node.name_locs):
+            if self._check_not_in(name, self.global_, "global", "nonlocal", loc) or \
+                    self._check_not_in(name, self.params, "a parameter", "nonlocal", loc):
+                continue
+
+            # nonlocal does not search prelude and global scopes
+            found = False
+            for outer_env in reversed(self.env_stack[2:]):
+                if name in outer_env:
+                    found = True
+                    break
+            if not found:
+                diag = diagnostic.Diagnostic("error",
+                    "cannot declare name '{name}' as nonlocal: it is not bound in any outer scope",
+                    {"name": name},
+                    loc, [node.keyword_loc])
+                self.engine.process(diag)
+                continue
+
+            self.nonlocal_.add(name)
+
+    def visit_ExceptHandler(self, node):
+        self.visit(node.type)
+        self._assignable(node.name)
+        for stmt in node.body:
+            self.visit(stmt)
+
+
+class ASTTypedRewriter(algorithm.Transformer):
+    """
+    :class:`ASTTypedRewriter` converts an untyped AST to a typed AST
+    where all type fields of non-literals are filled with fresh type variables,
+    and type fields of literals are filled with corresponding types.
+
+    :class:`ASTTypedRewriter` also discovers the scope of variable bindings
+    via :class:`LocalExtractor`.
+    """
+
+    def __init__(self, engine):
+        self.engine = engine
+        self.globals = None
+        self.env_stack = [prelude.globals()]
+
+    def _find_name(self, name, loc):
+        for typing_env in reversed(self.env_stack):
+            if name in typing_env:
+                return typing_env[name]
+        diag = diagnostic.Diagnostic("fatal",
+            "name '{name}' is not bound to anything", {"name":name}, loc)
+        self.engine.process(diag)
+
+    # Visitors that replace node with a typed node
+    #
+    def visit_Module(self, node):
+        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
+        extractor.visit(node)
+
+        node = asttyped.ModuleT(
+            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
+            body=node.body, loc=node.loc)
+        self.globals = node.typing_env
+
+        try:
+            self.env_stack.append(node.typing_env)
+            return self.generic_visit(node)
+        finally:
+            self.env_stack.pop()
+
+    def visit_FunctionDef(self, node):
+        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
+        extractor.visit(node)
+
+        node = asttyped.FunctionDefT(
+            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
+            signature_type=self._find_name(node.name, node.name_loc), return_type=types.TVar(),
+            name=node.name, args=node.args, returns=node.returns,
+            body=node.body, decorator_list=node.decorator_list,
+            keyword_loc=node.keyword_loc, name_loc=node.name_loc,
+            arrow_loc=node.arrow_loc, colon_loc=node.colon_loc, at_locs=node.at_locs,
+            loc=node.loc)
+
+        try:
+            self.env_stack.append(node.typing_env)
+            return self.generic_visit(node)
+        finally:
+            self.env_stack.pop()
+
+    def visit_arg(self, node):
+        return asttyped.argT(type=self._find_name(node.arg, node.loc),
+                             arg=node.arg, annotation=self.visit(node.annotation),
+                             arg_loc=node.arg_loc, colon_loc=node.colon_loc, loc=node.loc)
+
+    def visit_Num(self, node):
+        if isinstance(node.n, int):
+            typ = builtins.TInt()
+        elif isinstance(node.n, float):
+            typ = builtins.TFloat()
+        else:
+            diag = diagnostic.Diagnostic("fatal",
+                "numeric type {type} is not supported", {"type": node.n.__class__.__name__},
+                node.loc)
+            self.engine.process(diag)
+        return asttyped.NumT(type=typ,
+                             n=node.n, loc=node.loc)
+
+    def visit_Name(self, node):
+        return asttyped.NameT(type=self._find_name(node.id, node.loc),
+                              id=node.id, ctx=node.ctx, loc=node.loc)
+
+    def visit_NameConstant(self, node):
+        if node.value is True or node.value is False:
+            typ = builtins.TBool()
+        elif node.value is None:
+            typ = builtins.TNone()
+        return asttyped.NameConstantT(type=typ, value=node.value, loc=node.loc)
+
+    def visit_Tuple(self, node):
+        node = self.generic_visit(node)
+        return asttyped.TupleT(type=types.TTuple([x.type for x in node.elts]),
+                               elts=node.elts, ctx=node.ctx, loc=node.loc)
+
+    def visit_List(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.ListT(type=builtins.TList(),
+                              elts=node.elts, ctx=node.ctx, loc=node.loc)
+        return self.visit(node)
+
+    def visit_Attribute(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.AttributeT(type=types.TVar(),
+                                   value=node.value, attr=node.attr, ctx=node.ctx,
+                                   dot_loc=node.dot_loc, attr_loc=node.attr_loc, loc=node.loc)
+        return self.visit(node)
+
+    def visit_Subscript(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.SubscriptT(type=types.TVar(),
+                                   value=node.value, slice=node.slice, ctx=node.ctx,
+                                   loc=node.loc)
+        return self.visit(node)
+
+    def visit_BoolOp(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.BoolOpT(type=types.TVar(),
+                                op=node.op, values=node.values,
+                                op_locs=node.op_locs, loc=node.loc)
+        return self.visit(node)
+
+    def visit_UnaryOp(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.UnaryOpT(type=types.TVar(),
+                                 op=node.op, operand=node.operand,
+                                 loc=node.loc)
+        return self.visit(node)
+
+    def visit_BinOp(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.BinOpT(type=types.TVar(),
+                               left=node.left, op=node.op, right=node.right,
+                               loc=node.loc)
+        return self.visit(node)
+
+    def visit_Compare(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.CompareT(type=types.TVar(),
+                                 left=node.left, ops=node.ops, comparators=node.comparators,
+                                 loc=node.loc)
+        return self.visit(node)
+
+    def visit_IfExp(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.IfExpT(type=types.TVar(),
+                               test=node.test, body=node.body, orelse=node.orelse,
+                               if_loc=node.if_loc, else_loc=node.else_loc, loc=node.loc)
+        return self.visit(node)
+
+    def visit_ListComp(self, node):
+        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
+        extractor.visit(node)
+
+        node = asttyped.ListCompT(
+            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
+            type=types.TVar(),
+            elt=node.elt, generators=node.generators,
+            begin_loc=node.begin_loc, end_loc=node.end_loc, loc=node.loc)
+
+        try:
+            self.env_stack.append(node.typing_env)
+            return self.generic_visit(node)
+        finally:
+            self.env_stack.pop()
+
+    def visit_Call(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.CallT(type=types.TVar(),
+                              func=node.func, args=node.args, keywords=node.keywords,
+                              starargs=node.starargs, kwargs=node.kwargs,
+                              star_loc=node.star_loc, dstar_loc=node.dstar_loc,
+                              begin_loc=node.begin_loc, end_loc=node.end_loc, loc=node.loc)
+        return node
+
+    def visit_Lambda(self, node):
+        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
+        extractor.visit(node)
+
+        node = asttyped.LambdaT(
+            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
+            type=types.TVar(),
+            args=node.args, body=node.body,
+            lambda_loc=node.lambda_loc, colon_loc=node.colon_loc, loc=node.loc)
+
+        try:
+            self.env_stack.append(node.typing_env)
+            return self.generic_visit(node)
+        finally:
+            self.env_stack.pop()
+
+    def visit_ExceptHandler(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.ExceptHandlerT(
+            name_type=self._find_name(node.name, node.name_loc),
+            filter=node.type, name=node.name, body=node.body,
+            except_loc=node.except_loc, as_loc=node.as_loc, name_loc=node.name_loc,
+            colon_loc=node.colon_loc, loc=node.loc)
+        return node
+
+    def visit_Raise(self, node):
+        node = self.generic_visit(node)
+        if node.cause:
+            diag = diagnostic.Diagnostic("error",
+                "'raise from' syntax is not supported", {},
+                node.from_loc)
+            self.engine.process(diag)
+        return node
+
+    # Unsupported visitors
+    #
+    def visit_unsupported(self, node):
+        diag = diagnostic.Diagnostic("fatal",
+            "this syntax is not supported", {},
+            node.loc)
+        self.engine.process(diag)
+
+    # expr
+    visit_Dict = visit_unsupported
+    visit_DictComp = visit_unsupported
+    visit_Ellipsis = visit_unsupported
+    visit_GeneratorExp = visit_unsupported
+    visit_Set = visit_unsupported
+    visit_SetComp = visit_unsupported
+    visit_Str = visit_unsupported
+    visit_Starred = visit_unsupported
+    visit_Yield = visit_unsupported
+    visit_YieldFrom = visit_unsupported
+
+    # stmt
+    visit_Assert = visit_unsupported
+    visit_ClassDef = visit_unsupported
+    visit_Delete = visit_unsupported
+    visit_Import = visit_unsupported
+    visit_ImportFrom = visit_unsupported
diff --git a/artiq/compiler/typing.py b/artiq/compiler/transforms/inferencer.py
similarity index 68%
rename from artiq/compiler/typing.py
rename to artiq/compiler/transforms/inferencer.py
index c7ae71327..f78acea22 100644
--- a/artiq/compiler/typing.py
+++ b/artiq/compiler/transforms/inferencer.py
@@ -1,378 +1,6 @@
-from pythonparser import source, ast, algorithm, diagnostic, parse_buffer
 from collections import OrderedDict
-from . import asttyped, types, builtins
-
-# This visitor will be called for every node with a scope,
-# i.e.: class, function, comprehension, lambda
-class LocalExtractor(algorithm.Visitor):
-    def __init__(self, env_stack, engine):
-        super().__init__()
-        self.env_stack  = env_stack
-        self.engine     = engine
-
-        self.in_root    = False
-        self.in_assign  = False
-        self.typing_env = {}
-
-        # which names are global have to be recorded in the current scope
-        self.global_    = set()
-
-        # which names are nonlocal only affects whether the current scope
-        # gets a new binding or not, so we throw this away
-        self.nonlocal_  = set()
-
-        # parameters can't be declared as global or nonlocal
-        self.params     = set()
-
-        if len(self.env_stack) == 1:
-            self.env_stack.append(self.typing_env)
-
-    def visit_in_assign(self, node):
-        try:
-            self.in_assign = True
-            return self.visit(node)
-        finally:
-            self.in_assign = False
-
-    def visit_Assign(self, node):
-        self.visit(node.value)
-        for target in node.targets:
-            self.visit_in_assign(target)
-
-    def visit_For(self, node):
-        self.visit(node.iter)
-        self.visit_in_assign(node.target)
-        self.visit(node.body)
-        self.visit(node.orelse)
-
-    def visit_withitem(self, node):
-        self.visit(node.context_expr)
-        if node.optional_vars is not None:
-            self.visit_in_assign(node.optional_vars)
-
-    def visit_comprehension(self, node):
-        self.visit(node.iter)
-        self.visit_in_assign(node.target)
-        for if_ in node.ifs:
-            self.visit(node.ifs)
-
-    def visit_root(self, node):
-        if self.in_root:
-            return
-        self.in_root = True
-        self.generic_visit(node)
-
-    visit_Module       = visit_root # don't look at inner scopes
-    visit_ClassDef     = visit_root
-    visit_Lambda       = visit_root
-    visit_DictComp     = visit_root
-    visit_ListComp     = visit_root
-    visit_SetComp      = visit_root
-    visit_GeneratorExp = visit_root
-
-    def visit_FunctionDef(self, node):
-        if self.in_root:
-            self._assignable(node.name)
-        self.visit_root(node)
-
-    def _assignable(self, name):
-        if name not in self.typing_env and name not in self.nonlocal_:
-            self.typing_env[name] = types.TVar()
-
-    def visit_arg(self, node):
-        if node.arg in self.params:
-            diag = diagnostic.Diagnostic("error",
-                "duplicate parameter '{name}'", {"name": node.arg},
-                node.loc)
-            self.engine.process(diag)
-            return
-        self._assignable(node.arg)
-        self.params.add(node.arg)
-
-    def visit_Name(self, node):
-        if self.in_assign:
-            # code like:
-            # x = 1
-            # def f():
-            #   x = 1
-            # creates a new binding for x in f's scope
-            self._assignable(node.id)
-
-    def _check_not_in(self, name, names, curkind, newkind, loc):
-        if name in names:
-            diag = diagnostic.Diagnostic("error",
-                "name '{name}' cannot be {curkind} and {newkind} simultaneously",
-                {"name": name, "curkind": curkind, "newkind": newkind}, loc)
-            self.engine.process(diag)
-            return True
-        return False
-
-    def visit_Global(self, node):
-        for name, loc in zip(node.names, node.name_locs):
-            if self._check_not_in(name, self.nonlocal_, "nonlocal", "global", loc) or \
-                    self._check_not_in(name, self.params, "a parameter", "global", loc):
-               continue
-
-            self.global_.add(name)
-            self._assignable(name)
-            self.env_stack[1][name] = self.typing_env[name]
-
-    def visit_Nonlocal(self, node):
-        for name, loc in zip(node.names, node.name_locs):
-            if self._check_not_in(name, self.global_, "global", "nonlocal", loc) or \
-                    self._check_not_in(name, self.params, "a parameter", "nonlocal", loc):
-                continue
-
-            # nonlocal does not search prelude and global scopes
-            found = False
-            for outer_env in reversed(self.env_stack[2:]):
-                if name in outer_env:
-                    found = True
-                    break
-            if not found:
-                diag = diagnostic.Diagnostic("error",
-                    "cannot declare name '{name}' as nonlocal: it is not bound in any outer scope",
-                    {"name": name},
-                    loc, [node.keyword_loc])
-                self.engine.process(diag)
-                continue
-
-            self.nonlocal_.add(name)
-
-    def visit_ExceptHandler(self, node):
-        self.visit(node.type)
-        self._assignable(node.name)
-        for stmt in node.body:
-            self.visit(stmt)
-
-
-class ASTTypedRewriter(algorithm.Transformer):
-    """
-    :class:`ASTTypedRewriter` converts an untyped AST to a typed AST
-    where all type fields of non-literals are filled with fresh type variables,
-    and type fields of literals are filled with corresponding types.
-
-    :class:`ASTTypedRewriter` also discovers the scope of variable bindings
-    via :class:`LocalExtractor`.
-    """
-
-    def __init__(self, engine, globals={}):
-        self.engine = engine
-        self.env_stack = [globals]
-
-    def _find_name(self, name, loc):
-        for typing_env in reversed(self.env_stack):
-            if name in typing_env:
-                return typing_env[name]
-        diag = diagnostic.Diagnostic("fatal",
-            "name '{name}' is not bound to anything", {"name":name}, loc)
-        self.engine.process(diag)
-
-    # Visitors that replace node with a typed node
-    #
-    def visit_Module(self, node):
-        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
-        extractor.visit(node)
-
-        node = asttyped.ModuleT(
-            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
-            body=node.body, loc=node.loc)
-        return self.generic_visit(node)
-
-    def visit_FunctionDef(self, node):
-        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
-        extractor.visit(node)
-
-        node = asttyped.FunctionDefT(
-            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
-            signature_type=self._find_name(node.name, node.name_loc), return_type=types.TVar(),
-            name=node.name, args=node.args, returns=node.returns,
-            body=node.body, decorator_list=node.decorator_list,
-            keyword_loc=node.keyword_loc, name_loc=node.name_loc,
-            arrow_loc=node.arrow_loc, colon_loc=node.colon_loc, at_locs=node.at_locs,
-            loc=node.loc)
-
-        try:
-            self.env_stack.append(node.typing_env)
-            return self.generic_visit(node)
-        finally:
-            self.env_stack.pop()
-
-    def visit_arg(self, node):
-        return asttyped.argT(type=self._find_name(node.arg, node.loc),
-                             arg=node.arg, annotation=self.visit(node.annotation),
-                             arg_loc=node.arg_loc, colon_loc=node.colon_loc, loc=node.loc)
-
-    def visit_Num(self, node):
-        if isinstance(node.n, int):
-            typ = builtins.TInt()
-        elif isinstance(node.n, float):
-            typ = builtins.TFloat()
-        else:
-            diag = diagnostic.Diagnostic("fatal",
-                "numeric type {type} is not supported", {"type": node.n.__class__.__name__},
-                node.loc)
-            self.engine.process(diag)
-        return asttyped.NumT(type=typ,
-                             n=node.n, loc=node.loc)
-
-    def visit_Name(self, node):
-        return asttyped.NameT(type=self._find_name(node.id, node.loc),
-                              id=node.id, ctx=node.ctx, loc=node.loc)
-
-    def visit_NameConstant(self, node):
-        if node.value is True or node.value is False:
-            typ = builtins.TBool()
-        elif node.value is None:
-            typ = builtins.TNone()
-        return asttyped.NameConstantT(type=typ, value=node.value, loc=node.loc)
-
-    def visit_Tuple(self, node):
-        node = self.generic_visit(node)
-        return asttyped.TupleT(type=types.TTuple([x.type for x in node.elts]),
-                               elts=node.elts, ctx=node.ctx, loc=node.loc)
-
-    def visit_List(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.ListT(type=builtins.TList(),
-                              elts=node.elts, ctx=node.ctx, loc=node.loc)
-        return self.visit(node)
-
-    def visit_Attribute(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.AttributeT(type=types.TVar(),
-                                   value=node.value, attr=node.attr, ctx=node.ctx,
-                                   dot_loc=node.dot_loc, attr_loc=node.attr_loc, loc=node.loc)
-        return self.visit(node)
-
-    def visit_Subscript(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.SubscriptT(type=types.TVar(),
-                                   value=node.value, slice=node.slice, ctx=node.ctx,
-                                   loc=node.loc)
-        return self.visit(node)
-
-    def visit_BoolOp(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.BoolOpT(type=types.TVar(),
-                                op=node.op, values=node.values,
-                                op_locs=node.op_locs, loc=node.loc)
-        return self.visit(node)
-
-    def visit_UnaryOp(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.UnaryOpT(type=types.TVar(),
-                                 op=node.op, operand=node.operand,
-                                 loc=node.loc)
-        return self.visit(node)
-
-    def visit_BinOp(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.BinOpT(type=types.TVar(),
-                               left=node.left, op=node.op, right=node.right,
-                               loc=node.loc)
-        return self.visit(node)
-
-    def visit_Compare(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.CompareT(type=types.TVar(),
-                                 left=node.left, ops=node.ops, comparators=node.comparators,
-                                 loc=node.loc)
-        return self.visit(node)
-
-    def visit_IfExp(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.IfExpT(type=types.TVar(),
-                               test=node.test, body=node.body, orelse=node.orelse,
-                               if_loc=node.if_loc, else_loc=node.else_loc, loc=node.loc)
-        return self.visit(node)
-
-    def visit_ListComp(self, node):
-        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
-        extractor.visit(node)
-
-        node = asttyped.ListCompT(
-            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
-            type=types.TVar(),
-            elt=node.elt, generators=node.generators,
-            begin_loc=node.begin_loc, end_loc=node.end_loc, loc=node.loc)
-
-        try:
-            self.env_stack.append(node.typing_env)
-            return self.generic_visit(node)
-        finally:
-            self.env_stack.pop()
-
-    def visit_Call(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.CallT(type=types.TVar(),
-                              func=node.func, args=node.args, keywords=node.keywords,
-                              starargs=node.starargs, kwargs=node.kwargs,
-                              star_loc=node.star_loc, dstar_loc=node.dstar_loc,
-                              begin_loc=node.begin_loc, end_loc=node.end_loc, loc=node.loc)
-        return node
-
-    def visit_Lambda(self, node):
-        extractor = LocalExtractor(env_stack=self.env_stack, engine=self.engine)
-        extractor.visit(node)
-
-        node = asttyped.LambdaT(
-            typing_env=extractor.typing_env, globals_in_scope=extractor.global_,
-            type=types.TVar(),
-            args=node.args, body=node.body,
-            lambda_loc=node.lambda_loc, colon_loc=node.colon_loc, loc=node.loc)
-
-        try:
-            self.env_stack.append(node.typing_env)
-            return self.generic_visit(node)
-        finally:
-            self.env_stack.pop()
-
-    def visit_ExceptHandler(self, node):
-        node = self.generic_visit(node)
-        node = asttyped.ExceptHandlerT(
-            name_type=self._find_name(node.name, node.name_loc),
-            filter=node.type, name=node.name, body=node.body,
-            except_loc=node.except_loc, as_loc=node.as_loc, name_loc=node.name_loc,
-            colon_loc=node.colon_loc, loc=node.loc)
-        return node
-
-    def visit_Raise(self, node):
-        node = self.generic_visit(node)
-        if node.cause:
-            diag = diagnostic.Diagnostic("error",
-                "'raise from' syntax is not supported", {},
-                node.from_loc)
-            self.engine.process(diag)
-        return node
-
-    # Unsupported visitors
-    #
-    def visit_unsupported(self, node):
-        diag = diagnostic.Diagnostic("fatal",
-            "this syntax is not supported", {},
-            node.loc)
-        self.engine.process(diag)
-
-    # expr
-    visit_Dict = visit_unsupported
-    visit_DictComp = visit_unsupported
-    visit_Ellipsis = visit_unsupported
-    visit_GeneratorExp = visit_unsupported
-    visit_Set = visit_unsupported
-    visit_SetComp = visit_unsupported
-    visit_Str = visit_unsupported
-    visit_Starred = visit_unsupported
-    visit_Yield = visit_unsupported
-    visit_YieldFrom = visit_unsupported
-
-    # stmt
-    visit_Assert = visit_unsupported
-    visit_ClassDef = visit_unsupported
-    visit_Delete = visit_unsupported
-    visit_Import = visit_unsupported
-    visit_ImportFrom = visit_unsupported
-
+from pythonparser import algorithm, diagnostic, ast
+from .. import asttyped, types, builtins
 
 class Inferencer(algorithm.Visitor):
     """
@@ -444,7 +72,7 @@ class Inferencer(algorithm.Visitor):
     def visit_ListT(self, node):
         self.generic_visit(node)
         for elt in node.elts:
-            self._unify(node.type, builtins.TList(elt.type),
+            self._unify(node.type["elt"], elt.type,
                         node.loc, elt.loc, self._makenotes_elts(node.elts, "a list element"))
 
     def visit_AttributeT(self, node):
@@ -1173,77 +801,3 @@ class Inferencer(algorithm.Visitor):
         else:
             self._unify(self.function.return_type, node.value.type,
                         self.function.name_loc, node.value.loc, makenotes)
-
-class Printer(algorithm.Visitor):
-    """
-    :class:`Printer` prints ``:`` and the node type after every typed node,
-    and ``->`` and the node type before the colon in a function definition.
-
-    In almost all cases (except function definition) this does not result
-    in valid Python syntax.
-
-    :ivar rewriter: (:class:`pythonparser.source.Rewriter`) rewriter instance
-    """
-
-    def __init__(self, buf):
-        self.rewriter = source.Rewriter(buf)
-        self.type_printer = types.TypePrinter()
-
-    def rewrite(self):
-        return self.rewriter.rewrite()
-
-    def visit_FunctionDefT(self, node):
-        super().generic_visit(node)
-
-        self.rewriter.insert_before(node.colon_loc,
-                                    "->{}".format(self.type_printer.name(node.return_type)))
-
-    def visit_ExceptHandlerT(self, node):
-        super().generic_visit(node)
-
-        if node.name_loc:
-            self.rewriter.insert_after(node.name_loc,
-                                        ":{}".format(self.type_printer.name(node.name_type)))
-
-    def generic_visit(self, node):
-        super().generic_visit(node)
-
-        if hasattr(node, "type"):
-            self.rewriter.insert_after(node.loc,
-                                       ":{}".format(self.type_printer.name(node.type)))
-
-def main():
-    import sys, fileinput, os
-    from . import prelude
-
-    if len(sys.argv) > 1 and sys.argv[1] == '+diag':
-        del sys.argv[1]
-        def process_diagnostic(diag):
-            print("\n".join(diag.render(only_line=True)))
-            if diag.level == 'fatal':
-                exit()
-    else:
-        def process_diagnostic(diag):
-            print("\n".join(diag.render()))
-            if diag.level in ('fatal', 'error'):
-                exit(1)
-
-    engine = diagnostic.Engine()
-    engine.process = process_diagnostic
-
-    buf = source.Buffer("".join(fileinput.input()).expandtabs(),
-                        os.path.basename(fileinput.filename()))
-    parsed, comments = parse_buffer(buf, engine=engine)
-    typed = ASTTypedRewriter(globals=prelude.globals(), engine=engine).visit(parsed)
-    Inferencer(engine=engine).visit(typed)
-
-    printer = Printer(buf)
-    printer.visit(typed)
-    for comment in comments:
-        if comment.text.find("CHECK") >= 0:
-            printer.rewriter.remove(comment.loc)
-    print(printer.rewrite().source)
-
-
-if __name__ == "__main__":
-    main()
diff --git a/lit-test/compiler/typing/builtin_calls.py b/lit-test/compiler/inferencer/builtin_calls.py
similarity index 92%
rename from lit-test/compiler/typing/builtin_calls.py
rename to lit-test/compiler/inferencer/builtin_calls.py
index 82c750bf1..50597151f 100644
--- a/lit-test/compiler/typing/builtin_calls.py
+++ b/lit-test/compiler/inferencer/builtin_calls.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: bool:<constructor bool>():bool
diff --git a/lit-test/compiler/typing/coerce.py b/lit-test/compiler/inferencer/coerce.py
similarity index 95%
rename from lit-test/compiler/typing/coerce.py
rename to lit-test/compiler/inferencer/coerce.py
index 5b161ab30..3b0190c49 100644
--- a/lit-test/compiler/typing/coerce.py
+++ b/lit-test/compiler/inferencer/coerce.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 1 | 2
diff --git a/lit-test/compiler/typing/error_builtin_calls.py b/lit-test/compiler/inferencer/error_builtin_calls.py
similarity index 86%
rename from lit-test/compiler/typing/error_builtin_calls.py
rename to lit-test/compiler/inferencer/error_builtin_calls.py
index 858df6d4a..32ce8b294 100644
--- a/lit-test/compiler/typing/error_builtin_calls.py
+++ b/lit-test/compiler/inferencer/error_builtin_calls.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 a = 1
diff --git a/lit-test/compiler/typing/error_call.py b/lit-test/compiler/inferencer/error_call.py
similarity index 86%
rename from lit-test/compiler/typing/error_call.py
rename to lit-test/compiler/inferencer/error_call.py
index 2ff169faf..21ba5bdf6 100644
--- a/lit-test/compiler/typing/error_call.py
+++ b/lit-test/compiler/inferencer/error_call.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+1}: error: cannot call this expression of type int
diff --git a/lit-test/compiler/typing/error_coerce.py b/lit-test/compiler/inferencer/error_coerce.py
similarity index 96%
rename from lit-test/compiler/typing/error_coerce.py
rename to lit-test/compiler/inferencer/error_coerce.py
index feb7447b8..bf4a5dd36 100644
--- a/lit-test/compiler/typing/error_coerce.py
+++ b/lit-test/compiler/inferencer/error_coerce.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+1}: error: expected '<<' operand to be of integer type, not float
diff --git a/lit-test/compiler/typing/error_control_flow.py b/lit-test/compiler/inferencer/error_control_flow.py
similarity index 87%
rename from lit-test/compiler/typing/error_control_flow.py
rename to lit-test/compiler/inferencer/error_control_flow.py
index c5a913bdd..65e300511 100644
--- a/lit-test/compiler/typing/error_control_flow.py
+++ b/lit-test/compiler/inferencer/error_control_flow.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+1}: error: return statement outside of a function
diff --git a/lit-test/compiler/typing/error_exception.py b/lit-test/compiler/inferencer/error_exception.py
similarity index 80%
rename from lit-test/compiler/typing/error_exception.py
rename to lit-test/compiler/inferencer/error_exception.py
index 4172f7bde..4e4b340b5 100644
--- a/lit-test/compiler/typing/error_exception.py
+++ b/lit-test/compiler/inferencer/error_exception.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 try:
diff --git a/lit-test/compiler/typing/error_iterable.py b/lit-test/compiler/inferencer/error_iterable.py
similarity index 64%
rename from lit-test/compiler/typing/error_iterable.py
rename to lit-test/compiler/inferencer/error_iterable.py
index d3334a616..68ed1b002 100644
--- a/lit-test/compiler/typing/error_iterable.py
+++ b/lit-test/compiler/inferencer/error_iterable.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+1}: error: type int(width='a) is not iterable
diff --git a/lit-test/compiler/typing/error_local_unbound.py b/lit-test/compiler/inferencer/error_local_unbound.py
similarity index 61%
rename from lit-test/compiler/typing/error_local_unbound.py
rename to lit-test/compiler/inferencer/error_local_unbound.py
index fdf1b3047..6b4350157 100644
--- a/lit-test/compiler/typing/error_local_unbound.py
+++ b/lit-test/compiler/inferencer/error_local_unbound.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+1}: fatal: name 'x' is not bound to anything
diff --git a/lit-test/compiler/typing/error_locals.py b/lit-test/compiler/inferencer/error_locals.py
similarity index 93%
rename from lit-test/compiler/typing/error_locals.py
rename to lit-test/compiler/inferencer/error_locals.py
index 048295d2c..3a5185ca8 100644
--- a/lit-test/compiler/typing/error_locals.py
+++ b/lit-test/compiler/inferencer/error_locals.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 x = 1
diff --git a/lit-test/compiler/typing/error_return.py b/lit-test/compiler/inferencer/error_return.py
similarity index 88%
rename from lit-test/compiler/typing/error_return.py
rename to lit-test/compiler/inferencer/error_return.py
index fff45ed0b..ba4ddc2b3 100644
--- a/lit-test/compiler/typing/error_return.py
+++ b/lit-test/compiler/inferencer/error_return.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: ${LINE:+2}: error: cannot unify int(width='a) with NoneType
diff --git a/lit-test/compiler/typing/error_unify.py b/lit-test/compiler/inferencer/error_unify.py
similarity index 92%
rename from lit-test/compiler/typing/error_unify.py
rename to lit-test/compiler/inferencer/error_unify.py
index 076be96f4..e81537d29 100644
--- a/lit-test/compiler/typing/error_unify.py
+++ b/lit-test/compiler/inferencer/error_unify.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing +diag %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 a = 1
diff --git a/lit-test/compiler/typing/exception.py b/lit-test/compiler/inferencer/exception.py
similarity index 76%
rename from lit-test/compiler/typing/exception.py
rename to lit-test/compiler/inferencer/exception.py
index 32046157f..bfdbbfb7c 100644
--- a/lit-test/compiler/typing/exception.py
+++ b/lit-test/compiler/inferencer/exception.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: Exception:<constructor Exception>
diff --git a/lit-test/compiler/typing/gcd.py b/lit-test/compiler/inferencer/gcd.py
similarity index 80%
rename from lit-test/compiler/typing/gcd.py
rename to lit-test/compiler/inferencer/gcd.py
index c79052d89..e2d4b4779 100644
--- a/lit-test/compiler/typing/gcd.py
+++ b/lit-test/compiler/inferencer/gcd.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 
 def _gcd(a, b):
     if a < 0:
diff --git a/lit-test/compiler/typing/prelude.py b/lit-test/compiler/inferencer/prelude.py
similarity index 71%
rename from lit-test/compiler/typing/prelude.py
rename to lit-test/compiler/inferencer/prelude.py
index 1b70be299..643895e4a 100644
--- a/lit-test/compiler/typing/prelude.py
+++ b/lit-test/compiler/inferencer/prelude.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 # CHECK-L: x:<function len>
diff --git a/lit-test/compiler/typing/scoping.py b/lit-test/compiler/inferencer/scoping.py
similarity index 63%
rename from lit-test/compiler/typing/scoping.py
rename to lit-test/compiler/inferencer/scoping.py
index 1d1da612c..595daecf6 100644
--- a/lit-test/compiler/typing/scoping.py
+++ b/lit-test/compiler/inferencer/scoping.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 def f():
diff --git a/lit-test/compiler/typing/unify.py b/lit-test/compiler/inferencer/unify.py
similarity index 94%
rename from lit-test/compiler/typing/unify.py
rename to lit-test/compiler/inferencer/unify.py
index 9621c5b59..04c8aecbd 100644
--- a/lit-test/compiler/typing/unify.py
+++ b/lit-test/compiler/inferencer/unify.py
@@ -1,4 +1,4 @@
-# RUN: %python -m artiq.compiler.typing %s >%t
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
 a = 1