Example of parsing Get calls and resolving their product/subject ty…

…pes.

yields.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python2.7
+
+import ast
+import inspect
+
+
+class Get(object):
+  def __init__(self, *args):
+    pass
+
+
+def rule():
+  class RuleVisitor(ast.NodeVisitor):
+    def __init__(self, parent_function):
+      super(RuleVisitor, self).__init__()
+      self._parent_function = parent_function
+
+    def visit_Call(self, node):
+      if node.func.id != Get.__name__:
+        return
+
+      # TODO: Validation.
+      if len(node.args) == 2:
+        product_type, subject_constructor = node.args
+        self._parent_function._requests.append((product_type.id, subject_constructor.func.id))
+      elif len(node.args) == 3:
+        product_type, subject_type, _ = node.args
+        self._parent_function._requests.append((product_type.id, subject_type.id))
+      else:
+        raise Exception('Invalid {}: {}'.format(Get.__name__, node.args))
+
+  module_asts = {}
+  def wrapper(f):
+    print 'Creating @rule: `{}`'.format(f.__name__)
+
+    f._requests = []
+
+    caller_frame = inspect.stack()[1][0]
+    caller_filename = inspect.getframeinfo(caller_frame).filename
+
+    module_ast = module_asts.get(caller_filename)
+    if module_ast is None:
+      with open(caller_filename) as caller_file:
+        module_asts[caller_filename] = module_ast = ast.parse(caller_file.read())
+
+    for node in ast.iter_child_nodes(module_ast):
+      if isinstance(node, ast.FunctionDef) and node.name == f.__name__:
+        RuleVisitor(f).visit(node)
+
+    def resolve(name):
+      return caller_frame.f_globals.get(name) or caller_frame.f_builtins.get(name)
+
+    for product_type, subject_type in f._requests:
+      print '  found Get: {}, {}'.format(resolve(product_type), resolve(subject_type))
+    return f
+  return wrapper
+
+
+@rule()
+def do_this_one():
+  x = yield Get(int, str("thing"))
+  yield "other_thing"
+
+
+def but_not_this_one():
+  yield Get(int, str, "thing")
+
+
+@rule()
+def and_dont_get_confused_by():
+  def a_nested_thing():
+    return Get(int, str, "bottom")
+  yield a_nested_thing()
+
+
+@rule()
+def with_a_loop_even():
+  while True:
+    yield Get(int, str("this will not end... well"))