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Add an Align instance for lists.

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This commit is contained in:
Rob Rix 2016-03-07 09:42:53 -05:00
parent 05fa8a6aa5
commit 63782505af
1 changed files with 6 additions and 0 deletions
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6
src/Data/Align.hs
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@ -6,3 +6,9 @@ class Functor f => Align f where
align a b = alignWith id a b
alignWith :: (These a b -> c) -> f a -> f b -> f c
alignWith f a b = f <$> align a b
instance Align [] where
nil = []
alignWith f as [] = f . This <$> as
alignWith f [] bs = f . That <$> bs
alignWith f (a : as) (b : bs) = f (These a b) : alignWith f as bs