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The Align instance for List pads from the start.

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This commit is contained in:
Rob Rix 2016-03-10 20:05:46 -05:00
parent c750a98f4b
commit 37865cc509
1 changed files with 4 additions and 3 deletions
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7
src/Data/Align.hs
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@ -12,9 +12,10 @@ class Functor f => Align f where
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
align as bs | la < lb = (That <$> take (lb - la) bs) ++ align as (drop (lb - la) bs)
| la > lb = (This <$> take (la - lb) as) ++ align (drop (la - lb) as) bs
| otherwise = zipWith These as bs
where (la, lb) = (length as, length bs)
instance Align Maybe where
nil = Nothing