Suite de Conway en Haskell

Conway.hs

module Conway where

-- https://fr.wikipedia.org/wiki/Suite_de_Conway

-- 1211
-- Il y a trois éléments :
-- - la liste déjà traitée,
-- - le chiffre en cours de comptage,
-- - la liste restant à traiter

-- ([],[],[1,2,1,1])
-- ([],[1,1][2,1,1])
-- ([1,1],[1,2],[1,1])
-- ([1,1,1,2],[1,1][1])
-- ([1,1,1,2],[2,1][])
-- ([1,1,1,2,2,1],[][])

type Processed = [Int]
type ToProcess = [Int]

conway :: ToProcess -> Processed
conway ns = recur [] ns

recur :: Processed -> ToProcess -> Processed
recur ps [] = ps
recur ps ts = recur (ps++counted) rest
  where (counted, rest) = countSameNumbers ts

countSameNumbers :: ToProcess -> (Processed,ToProcess)
countSameNumbers ns@(n:_) = ([length sameNs, n], rest)
  where sameNs = takeWhile (== n) ns
        rest = dropWhile (== n) ns
countSameNumbers _ = error "wrong state"