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mstksg/init-last.hs

Created June 6, 2018 07:34
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Init and Last
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init-last.hs
import Data.Bifunctor (first)
import Data.List (foldl')
type Diff a = [a] -> [a]
match :: [a] -> Either () ([a], a)
match = (fmap . first) ($[]) -- extract the Diff list
. foldl' go (Left ())
where
go :: Either () (Diff a, a)
-> a
-> Either () (Diff a, a)
go (Left _ ) x = Right (id , x)
go (Right (ys, y)) x = Right (ys . (y:), x)
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