The learning process

gistfile1.hs

-- Kata http://www.codewars.com/kata/551204b7509063d9ba000b45/haskell

mainDiagonalProduct :: Num a => [[a]] -> a
-- My implementation
mainDiagonalProduct [] = 1
mainDiagonalProduct mat =
	mainDiagonalProduct' mat ((length mat) - 1)
	
	where
		mainDiagonalProduct' mat 0 = (head . head) mat
		mainDiagonalProduct' mat index = 
			((mat !! index) !! index) * (mainDiagonalProduct' mat (index - 1))
			
			
-- Good implementation
mainDiagonalProduct mat = product $ zipWith (!!) mat [1..]