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| author | Dylan Meysmans <contact@mettekou.com> | 2016-07-20 09:54:55 +0200 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2016-07-20 15:17:50 +0200 |
| commit | a0f83a628cc6a00f948662f88e711c2a37bfda60 (patch) | |
| tree | 0e69761cd0e5735a1704dd2f8c08cca1ab81fec5 | |
| parent | cac3fb06f4b282eee21159c364c4d08e8fdedce9 (diff) | |
| download | haskell-a0f83a628cc6a00f948662f88e711c2a37bfda60.tar.gz | |
Data.Either: Add fromLeft and fromRight (#12402)
Reviewers: austin, hvr, RyanGlScott, bgamari
Reviewed By: RyanGlScott, bgamari
Subscribers: RyanGlScott, thomie
Differential Revision: https://phabricator.haskell.org/D2403
GHC Trac Issues: #12402
| -rw-r--r-- | docs/users_guide/8.2.1-notes.rst | 2 | ||||
| -rw-r--r-- | libraries/base/Data/Either.hs | 36 | ||||
| -rw-r--r-- | libraries/base/changelog.md | 2 |
3 files changed, 40 insertions, 0 deletions
diff --git a/docs/users_guide/8.2.1-notes.rst b/docs/users_guide/8.2.1-notes.rst index 5f45bf1002..27b49efa7e 100644 --- a/docs/users_guide/8.2.1-notes.rst +++ b/docs/users_guide/8.2.1-notes.rst @@ -98,6 +98,8 @@ See ``changelog.md`` in the ``base`` package for full release notes. - Version number 4.10.0.0 (was 4.9.0.0) +- ``Data.Either`` now provides ``fromLeft`` and ``fromRight`` + binary ~~~~~~ diff --git a/libraries/base/Data/Either.hs b/libraries/base/Data/Either.hs index 8bef30be9c..437d87cb5e 100644 --- a/libraries/base/Data/Either.hs +++ b/libraries/base/Data/Either.hs @@ -24,6 +24,8 @@ module Data.Either ( rights, isLeft, isRight, + fromLeft, + fromRight, partitionEithers, ) where @@ -280,6 +282,40 @@ isRight :: Either a b -> Bool isRight (Left _) = False isRight (Right _) = True +-- | Return the contents of a 'Left'-value or a default value otherwise. +-- +-- @since 4.10.0.0 +-- +-- ==== __Examples__ +-- +-- Basic usage: +-- +-- >>> fromLeft 1 (Left 3) +-- 3 +-- >>> fromLeft 1 (Right "foo") +-- 1 +-- +fromLeft :: a -> Either a b -> a +fromLeft _ (Left a) = a +fromLeft a _ = a + +-- | Return the contents of a 'Right'-value or a default value otherwise. +-- +-- @since 4.10.0.0 +-- +-- ==== __Examples__ +-- +-- Basic usage: +-- +-- >>> fromRight 1 (Right 3) +-- 3 +-- >>> fromRight 1 (Left "foo") +-- 1 +-- +fromRight :: b -> Either a b -> b +fromRight _ (Right b) = b +fromRight b _ = b + -- instance for the == Boolean type-level equality operator type family EqEither a b where EqEither ('Left x) ('Left y) = x == y diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md index ecf6a82df6..996456f0e6 100644 --- a/libraries/base/changelog.md +++ b/libraries/base/changelog.md @@ -14,6 +14,8 @@ * `New modules `Data.Bifoldable` and `Data.Bitraversable` (previously defined in the `bifunctors` package) (#10448) + * `Data.Either` now provides `fromLeft` and `fromRight` (#12402) + ## 4.9.0.0 *May 2016* * Bundled with GHC 8.0 |