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josephcsible/UglyMap.hs

Created February 4, 2021 20:01
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UglyMap.hs
import Control.Monad.State
import Data.Traversable
{-
>>> uglyMap (,,) "abc"
[('a',0,"abc"),('b',1,"abc"),('c',2,"abc")]
-}
uglyMap :: Traversable t => (a -> Int -> t a -> b) -> t a -> t b
uglyMap f xs = flip evalState 0 $ for xs $ \x -> do
i <- get
modify (+ 1)
pure $ f x i xs
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