main :: IO ()
main =
  do putStr "pocet radku: "                                  -- prompt
     n <- getLine >>= return . read                          -- nacteni cisla
     if n > 0
        then do putStr (unlines (map showLine (take n pt)))  -- vypis trojuhelnika
                main                                         --   a opakovani
        else return ()                                       -- ukonceni

pt :: [[Integer]]                               -- Pascaluv trojuhelnik
pt  = iterate (\r -> zipWith (+) ([0]++r) (r++[0])) [1]

showLine   :: [Integer] -> String                        -- vypis radku
showLine r = replicate m ' ' ++ concat (map showBox r)
             where m = abs (ll - length r * bwi) `div` 2

showBox  :: Integer -> String                            -- vypis prvku
showBox k = replicate p ' ' ++ sk ++ replicate r ' '
            where  sk = show k
                   l  = bwi - length sk
                   r = l `div` 2
                   p = l - r

bwi, ll :: Int
bwi = 5        -- max sirka cisla
ll = 80        -- delka radku na vystupu