Haskell Quiz/PP Pascal/Solution Ltriant

module Main where
 
import System.Environment ( getArgs )
 
fac n = product [1..n]
nck n k = (fac n) `div` ((fac $ n - k) * (fac k))
space_len n = mylength $ show $ (n-1) `nck` ((n-1) `div` 2)
mylength = toInteger . length
 
indent n t =
    (concat $ replicate (fromInteger $ (n-p) * space_len n)  " "):t
    where p = mylength t
 
space_out n t =
    map (\x -> show x ++ (concat $ replicate (num_spaces x) " ")) t
    where num_spaces x = fromInteger $ (2 * space_len n) - (mylength $ show x)
 
pp_pascal n =
    map (concat . indent n . space_out n) $ f 0 n
    where f acc n | acc == n  = []
                  | otherwise = (map (nck acc) [0..acc]):(f (acc+1) n)
 
main =
    do args <- getArgs
       case args of
         [v] -> mapM_ putStrLn $ pp_pascal (read v :: Integer)
         _   -> error "No argument specified."