-- 8 Queens in Haskell
-- by Harold Lee
-- harold at hotelling dot net

queens :: [[[Int]]] -- hugs needs this, but ghc does not
queens = map return [1..4] : map next queens
    where next qs = [a:b | a <- [1..8], b <- qs, safe a b 1]

safe x (y:ys) n = notElem x [y, y+n, y-n] && safe x ys (n+1)
safe x _ _ = True

draw n = (take (n-1) (repeat '.')) ++ "Q" ++ (take (8-n) (repeat '.')) ++ "\n"

main = do putStr $ concat $ map draw $ head $ queens !! 7