Pascal's triangle.hs

-- This is how Haskell newb (me) writes Pascal's triangle

-- evolution of each row

pascal [1] = [1, 1]
pascal (x:xs) = pascal2 (x:xs) [1]
 
pascal2 (x:y:xs) o | xs == []   = (1:(x+y):o)
		   | otherwise  = pascal2 (y:xs) ((x+y):o)


-- whole triangle

pascaln n = pascaln2 n [] [1]

pascaln2 n t r  | n == 0  = reverse (r:t)
		| n > 0   = pascaln2 (n-1) (r:t) (pascal r)   


-- usage

Main> pascaln 5
[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]