Either.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# OPTIONS_GHC -Wall #-}

module Papa.Base.Data.Either (
  module P,
  lefts,
  rights,
  fromLeft,
  fromRight,
) where

import Control.Applicative ( Applicative(pure) )
import Control.Category ( Category((.), id) )
import Control.Lens ( _Left, _Right, Traversal )
import Data.Either as P (
  Either (Left, Right),
  either,
  partitionEithers,
 )
import Data.Traversable ( Traversable(traverse) )

{-# INLINE lefts #-}
lefts :: Traversable f => Traversal (f (Either a b)) (f (Either a' b)) a a'
lefts = traverse . _Left

{-# INLINE rights #-}
rights :: Traversable f => Traversal (f (Either a b)) (f (Either a b')) b b'
rights = traverse . _Right

{-# INLINE fromLeft #-}
fromLeft :: a -> Either a b -> a
fromLeft x = either id (pure x)

{-# INLINE fromRight #-}
fromRight :: b -> Either a b -> b
fromRight x = either (pure x) id