Implement lambdas.

compiler/expr_visitor.py

@@ -239,6 +239,12 @@ class ExprVisitor(ast.NodeVisitor):
       self.writer.write('{} = {}'.format(result.name, v.expr))
     return result
 
+  def visit_Lambda(self, node):
+    ret = ast.Return(node.body, lineno=node.lineno)
+    func_node = ast.FunctionDef(
+        name='<lambda>', args=node.args, body=[ret])
+    return self.visit_function_inline(func_node)
+
   def visit_List(self, node):
     with self._visit_seq_elts(node.elts) as elems:
       result = self.block.alloc_temp()
@@ -451,5 +457,4 @@ class ExprVisitor(ast.NodeVisitor):
     msg = 'node not yet implemented: ' + type(node).__name__
     raise util.ParseError(node, msg)
 
-  visit_Lambda = _node_not_implemented
   visit_SetComp = _node_not_implemented

compiler/expr_visitor_test.py

@@ -151,6 +151,12 @@ class ExprVisitorTest(unittest.TestCase):
   testIfExprNested = _MakeExprTest(
       '"foo" if "" else "bar" if 0 else "baz"')
 
+  testLambda = _MakeExprTest('(lambda: 123)()')
+  testLambda = _MakeExprTest('(lambda a, b: (a, b))("foo", "bar")')
+  testLambda = _MakeExprTest('(lambda a, b=3: (a, b))("foo")')
+  testLambda = _MakeExprTest('(lambda *args: args)(1, 2, 3)')
+  testLambda = _MakeExprTest('(lambda **kwargs: kwargs)(x="foo", y="bar")')
+
   testListEmpty = _MakeLiteralTest([])
   testListNonEmpty = _MakeLiteralTest([1, 2])