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MaybeBoth is a Crosswalk.

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This commit is contained in:
Rob Rix 2016-03-11 16:49:24 -05:00
parent eaf8228932
commit f8afe6208a
1 changed files with 4 additions and 0 deletions
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src/Data/Functor/Both.hs
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@ -1,6 +1,7 @@
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Data.Functor.Both where
import Data.Align
import Data.Bifunctor
import Data.Bifunctor.These
import Prelude hiding (zipWith, fst, snd)
@ -53,3 +54,6 @@ newtype MaybeBoth a = MaybeBoth { runMaybeBoth :: Both (Maybe a) }
instance Applicative MaybeBoth where
pure = MaybeBoth . pure . Just
MaybeBoth (Both (f, g)) <*> MaybeBoth (Both (a, b)) = MaybeBoth (both (f <*> a) (g <*> b))
instance Crosswalk MaybeBoth where
crosswalk f (MaybeBoth ab) = runBothWith (alignWith (MaybeBoth . maybeBothOfThese)) (maybe nil f <$> ab)