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scott-fleischman/DeBruijn.hs

Created December 20, 2018 22:34
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DeBruijn Haskell type class
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DeBruijn.hs
-- https://twitter.com/pigworker/status/1068897189227913223
newtype B t = B t
class DeBruijn d where
deBruijn :: Applicative f => (s -> Int -> f t) -> d s -> Int -> f (d t)
instance DeBruijn B where
deBruijn f (B s) i = B <$> f s (i + 1)
deBruijnDefault = ala' Compose traverse
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