Readme1.test

# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
#
--type-backward Readme1.MyMaybe
===
 module Readme1 where

 maybe :: b -> (a -> b) -> Maybe a -> b
 maybe d f mb = case mb of
   Nothing -> d
   Just x -> f x

 type MyMaybe = Maybe Int

 {-# RULES "myRule" forall x. maybe Nothing Just x = x #-}

-foo :: Maybe Int
+foo :: MyMaybe
 foo = maybe Nothing Just (Just 5)