Warning: dumb (& dumber)

Euler_11.hs

greatestProduct :: [[Int]] -> Int
greatestProduct mat = _greatestProduct (0,0) mat 0

_greatestProduct :: (Int,Int) -> [[Int]] -> Int -> Int
_greatestProduct (20,y) mat prev = prev
_greatestProduct coord mat prev
	| current > prev = _greatestProduct nextC mat current
	| otherwise = _greatestProduct nextC mat prev
	where 	nextC = (nextCoord coord)
		maxVert = 	(max (up coord mat) (down coord mat))
		maxHor = 	(max (left coord mat) (right coord mat))
		max1 = 		(max maxVert maxHor)
		maxDiagUp = 	(max (upLeft coord mat) (upRight coord mat))
		maxDiagDown = 	(max (downLeft coord mat) (downRight coord mat))
		max2 = 		(max maxDiagUp maxDiagDown)
		current = 	(max max1 max2)

up :: (Int,Int) -> [[Int]] -> Int
up (x,y) mat
	| x < 3 = 0
	| otherwise = (mat !! x !! y) * (mat !! (x-1) !! y) * (mat !! (x-2) !! y) * (mat !! (x-3) !! y)

down :: (Int,Int) -> [[Int]] -> Int
down (x,y) mat
	| x > 16 = 0
	| otherwise = (mat !! x !! y) * (mat !! (x+1) !! y) * (mat !! (x+2) !! y) * (mat !! (x+3) !! y)

right :: (Int,Int) -> [[Int]] -> Int
right (x,y) mat
        | (y > 16) = 0
        | otherwise = (x0 !! y) * (x0 !! (y+1)) * (x0 !! (y+2)) * (x0 !! (y+3))
	where x0 = head mat

left :: (Int,Int) -> [[Int]] -> Int
left (x,y) mat
        | (y < 3) = 0
        | otherwise = (x0 !! y) * (x0 !! (y-1)) * (x0 !! (y-2)) * (x0 !! (y-3))
	where x0 = head mat

upLeft :: (Int,Int) -> [[Int]] -> Int
upLeft (x,y) mat
	| (x < 3) || (y < 3) = 0
	| otherwise = (mat !! x !! y) * (mat !! (x-1) !! (y-1)) * (mat !! (x-2) !! (y-2)) * (mat !! (x-3) !! (y-3))

upRight :: (Int,Int) -> [[Int]] -> Int
upRight (x,y) mat
	| (x < 3) || (y > 16) = 0
	| otherwise = (mat !! x !! y) * (mat !! (x-1) !! (y+1)) * (mat !! (x-2) !! (y+2)) * (mat !! (x-3) !! (y+3))


downLeft :: (Int,Int) -> [[Int]] -> Int
downLeft (x,y) mat
	| (x > 16) || (y < 3)  = 0
	| otherwise = (mat !! x !! y) * (mat !! (x+1) !! (y-1)) * (mat !! (x+2) !! (y-2)) * (mat !! (x+3) !! (y-3))	


downRight :: (Int,Int) -> [[Int]] -> Int
downRight (x,y) mat
        | (x > 16) || (y > 16)  = 0
        | otherwise = (mat !! x !! y) * (mat !! (x+1) !! (y+1)) * (mat !! (x+2) !! (y+2)) * (mat !! (x+3) !! (y+3))


nextCoord :: (Int,Int) -> (Int,Int)
nextCoord coord = let 	y' = (snd coord) + 1
			x = (fst coord)
			newx = (if (y' < 20) then x else (x+1))
			newy = (y' `mod` 20) in (newx,newy)