-- Copyright 2022 United States Government as represented by the Administrator
-- of the National Aeronautics and Space Administration. All Rights Reserved.
--
-- Disclaimers
--
-- Licensed under the Apache License, Version 2.0 (the "License"); you may
-- not use this file except in compliance with the License. You may obtain a
-- copy of the License at
--
--      https://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-- License for the specific language governing permissions and limitations
-- under the License.
--
-- | Auxiliary functions for working with values of type 'Either'.
module Data.Either.Extra
    ( makeLeft
    , mapLeft
    )
  where

-- | Replace the left value in an @Either@.
makeLeft :: c -> Either a b -> Either c b
makeLeft :: forall c a b. c -> Either a b -> Either c b
makeLeft c
c (Left a
_)  = c -> Either c b
forall a b. a -> Either a b
Left c
c
makeLeft c
_ (Right b
x) = b -> Either c b
forall a b. b -> Either a b
Right b
x

-- | Apply a transformation only to the 'Left' values of an 'Either'.
--
-- Left counterpart of 'fmap'.
mapLeft :: (a -> c) -> Either a b -> Either c b
mapLeft :: forall a c b. (a -> c) -> Either a b -> Either c b
mapLeft a -> c
f (Left a
x)  = c -> Either c b
forall a b. a -> Either a b
Left (a -> c
f a
x)
mapLeft a -> c
_ (Right b
x) = b -> Either c b
forall a b. b -> Either a b
Right b
x