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{-# LANGUAGE NoImplicitPrelude #-}
module Data.Either where
import Data.Bool
import Data.List -- for foldr
import Data.Eq
data Either a b = Left a | Right b
either f g (Left l) = f l
either f g (Right r) = g r
lefts xs = [ l | Left l <- xs]
rights xs = [ r | Right r <- xs]
isLeft (Left _) = True
isLeft _ = False
isRight (Right _) = True
isRight _ = False
fromLeft _ (Left l) = l
fromLett l _ = l
fromRight _ (Right r) = r
fromRight r _ = r
partitionEithers = foldr (either left right) ([], [])
where left a ~(l, r) = (a:l, r)
right a ~(l, r) = (l, a:r)
instance (Eq a, Eq b) => Eq (Either a b) where
Left x == Left y = x == y
Right x == Right y = x == y
_ == _ = False
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