gistfile1.hs

import Data.List (inits)
  
rest :: String -> String -> [(Char, String)]
rest [] _ = []
rest (x:xs) ys = (x, xs ++ ys) : rest xs (x:ys)


permutations :: String -> [String]
permutations [x] = [[x]]
permutations xs = do (x, xs) <- rest xs ""
                     p <- permutations xs
                     return (x : p)

checkNumber :: String -> Bool
checkNumber = all (\(i, num) -> read num `mod` i == 0) . zip [1..] . tail . inits

findNumbers = filter checkNumber (permutations "123456789")

LIST MONAD