Give all possible permutations given a list of lists such that each list defines the set of characters for that particular index of the key. Whereby the top level list is the same length as the overall key.

constraint_permutations.hs

-- The following holds true permuteAll [ [ 'a','b' ], [ 'c','d' ] ] => [ ['a','c'],['a','d'], ['b','c'], ['b','d'] ]

permuteAll :: [[a]] -> [[a]]
permuteAll []     = []
permuteAll (x:[]) = splitEvery 1 x
permuteAll (x:xs) = foldr (++) [] $ map f x
    where
        f :: a -> [[a]]
        f x' = map ( \y -> (x':y) ) (permuteAll xs)