Expose fromLeft and fromRight

CHANGES.md

@@ -1,3 +1,8 @@
+0.2.3
+=====
+
+* Expose `fromLeft` and `fromRight`.
+
 0.2.2
 =====
 

src/Protolude/Either.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE Safe #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 
@@ -8,12 +9,27 @@ module Protolude.Either (
 , rightToMaybe
 , maybeEmpty
 , maybeToEither
+, fromLeft
+, fromRight
 ) where
 
 import Data.Function (const)
 import Data.Monoid (Monoid, mempty)
 import Data.Maybe (Maybe(..), maybe)
 import Data.Either (Either(..), either)
+#if MIN_VERSION_base(4,10,0)
+import Data.Either (fromLeft, fromRight)
+#else
+-- | Return the contents of a 'Right'-value or a default value otherwise.
+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.
+fromRight :: b -> Either a b -> b
+fromRight _ (Right b) = b
+fromRight b _         = b
+#endif
 
 leftToMaybe :: Either l r -> Maybe l
 leftToMaybe = either Just (const Nothing)