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Discussion on: Daily Challenge #53 - Faro Shuffle

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Replies for: Haskell: faroShuffle :: [a] -> [a] faroShuffle ls = let mid = (length ls) `div` 2 fst = take mid ls ...

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swizzard profile image
sam • 
import Control.Arrow (arr, (&&&))

faroShuffle :: [a] -> [a]
faroShuffle a = let d = length a `div` 2
                in concat $
                   uncurry (zipWith (\a b -> [a, b])) $
                   (arr (take d)) &&& (arr (drop d)) a

i feel in my bones there's wholly point-free way to do it but can't quite get there right now

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craigmc08 profile image
Craig McIlwrath •

I managed to get it point free!

import Control.Arrow (arr, (&&&))

faroShuffle :: [a] -> [a]
faroShuffle = concat .
              uncurry (zipWith (\a b -> [a, b])) .
              uncurry splitAt .
              ((arr ((`div`2) . length)) &&& (arr id))

I remember looking for the splitAt function when I was writing my first answer, not sure how I missed it in hoogle.

Also, I've never seen Control.Arrow before (I'm pretty new to Haskell). Seems useful.