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phadej/Folds.hs

Created May 19, 2022 19:18
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Folds.hs
import Data.Coerce
import Data.Monoid
-- This combinator is based on ala' from Conor McBride's work on Epigram.
alaf :: (Coercible n o, Coercible n' o')
=> (o -> n) -> ((a -> n) -> b -> n') -> (a -> o) -> b -> o'
alaf _ = coerce
myfoldl :: Foldable t => (b -> a -> b) -> b -> t a -> b
myfoldl f z xs = alaf (Dual . Endo) foldMap (flip f) xs z
--
-- >>> myreverse "keep it simple"
-- "elpmis ti peek"
--
myreverse :: [a] -> [a]
myreverse = myfoldl (flip (:)) []
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