Actually, this is better (and no less clear): import Data.List queens n = q [] [0..n-1] where q s [] = [[]] q s as = concatMap (\a -> q (a:s) (delete

Actually, this is better (and no less clear): import Data.List queens n = q [] [0..n-1] where q s [] = [[]] q s as = concatMap (\a -> q (a:s) (delete a as)) (filter (f 1 s) as) f _ [] a = True f n (b:s) a = a /= b+n && a /= b-n && f (n+1) s a main = print $ length (queens 8) Undoubtedly functional, the question is whether it is improved eg. by using folds instead of explicit recursion, or replacing concatMap with monadic join.