# 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.
#
--fold Readme3.maybe
===
 module Readme3 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. case x of
-            Nothing -> Nothing
-            Just x1 -> Just x1 = x #-}
+{-# RULES "myRule" forall x. maybe Nothing Just x = x #-}

 foo :: MyMaybe
-foo = case Just 5 of
-  Nothing -> Nothing
-  Just x -> Just x
+foo = maybe Nothing Just (Just 5)