Demonstrate the () ==> constant can not be parsed

src/__Private/codegen/data/LambdaBody.SyntaxExample.hack

@@ -0,0 +1,15 @@
+/*
+ *  Copyright (c) 2017-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ */
+namespace Facebook\HHAST\__Private\SyntaxExamples;
+
+function lambda_body(): void {
+  () ==> Qualified\CONSTANT;
+  () ==> CONSTANT;
+  () ==> 1 + CONSTANT;
+}