main.hs

import System.Environment (getArgs)

data Dir = U | R deriving(Show)
type Link = [Dir]

shuf :: Link -> Int -> Int -> [Link]
shuf ds 0 0 = [ds]
shuf ds 0 q = shuf (R:ds) 0 (q-1)
shuf ds p 0 = shuf (U:ds) (p-1) 0
shuf ds p q =
    up ++ right
        where
            up    = shuf (U:ds) (p-1) q
            right = shuf (R:ds) p (q-1)

print_permute ylen xlen = do
    sequence_ $ map print $ shuf [] ylen xlen

main = do
    args <- getArgs
    case args of
        [xlen,ylen] -> print_permute (read ylen) (read xlen)
        _ -> putStrLn "need exactly two arguments"