関数型プログラミング言語Haskell Part30 [無断転載禁止]©2ch.net

[995 デフォルトの名無しさん 2017/09/26(火) 10:46:10.91 ID:cHfS1yYI]

inter :: a -> [[a]] -> [[[a]]]
inter x = go
 where
   go [] = []
   go (y:ys) = ((x:y):ys) : map (y:) (go ys)

part :: Int -> [a] ->[[[a]]]
part _ [] = []
part 1 xs = [[xs]]
part k (x:xs) = map ([x]:) prev_ks ++ concatMap (inter x) ks
 where
   prev_ks = part (k-1) xs
   ks = part k xs

main = print $ part 3 [1..4]