Project Euler, Problem #11, Haskell

-- The task: find four adjacent numbers with the maximum product. The
-- numbers should form a line: horizontal, vertical, or diagonal.
-- Calculate the product.

m :: [[Integer]]
m = [[8,   2, 22, 97, 38, 15,  0, 40,  0, 75,  4,  5,  7, 78, 52, 12, 50, 77, 91,  8],
     [49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48,  4, 56, 62,  0],
     [81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30,  3, 49, 13, 36, 65],
     [52, 70, 95, 23,  4, 60, 11, 42, 69, 24, 68, 56,  1, 32, 56, 71, 37,  2, 36, 91],
     [22, 31, 16, 71, 51, 67, 63, 89, 41, 92, 36, 54, 22, 40, 40, 28, 66, 33, 13, 80],
     [24, 47, 32, 60, 99,  3, 45,  2, 44, 75, 33, 53, 78, 36, 84, 20, 35, 17, 12, 50],
     [32, 98, 81, 28, 64, 23, 67, 10, 26, 38, 40, 67, 59, 54, 70, 66, 18, 38, 64, 70],
     [67, 26, 20, 68,  2, 62, 12, 20, 95, 63, 94, 39, 63,  8, 40, 91, 66, 49, 94, 21],
     [24, 55, 58,  5, 66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72],
     [21, 36, 23,  9, 75,  0, 76, 44, 20, 45, 35, 14,  0, 61, 33, 97, 34, 31, 33, 95],
     [78, 17, 53, 28, 22, 75, 31, 67, 15, 94,  3, 80,  4, 62, 16, 14,  9, 53, 56, 92],
     [16, 39,  5, 42, 96, 35, 31, 47, 55, 58, 88, 24,  0, 17, 54, 24, 36, 29, 85, 57],
     [86, 56,  0, 48, 35, 71, 89,  7,  5, 44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58],
     [19, 80, 81, 68,  5, 94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77,  4, 89, 55, 40],
     [4,  52,  8, 83, 97, 35, 99, 16,  7, 97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66],
     [88, 36, 68, 87, 57, 62, 20, 72,  3, 46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69],
     [4,  42, 16, 73, 38, 25, 39, 11, 24, 94, 72, 18,  8, 46, 29, 32, 40, 62, 76, 36],
     [20, 69, 36, 41, 72, 30, 23, 88, 34, 62, 99, 69, 82, 67, 59, 85, 74,  4, 36, 16],
     [20, 73, 35, 29, 78, 31, 90,  1, 74, 31, 49, 71, 48, 86, 81, 16, 23, 57,  5, 54],
     [1,  70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52,  1, 89, 19, 67, 48]]

hm :: Integer
hm =
  maximum
    [ m !! x !! y * m !! x !! (y + 1) * m !! x !! (y + 2) * m !! x !! (y + 3)
    | x <- [0 .. 19]
    , y <- [0 .. 16]
    ]

vm :: Integer
vm =
  maximum
    [ m !! x !! y * m !! (x + 1) !! y * m !! (x + 2) !! y * m !! (x + 3) !! y
    | x <- [0 .. 16]
    , y <- [0 .. 19]
    ]

dr :: Integer
dr =
  maximum
    [ m !! x !! y * m !! (x + 1) !! (y + 1) * m !! (x + 2) !! (y + 2) *
    m !! (x + 3) !! (y + 3)
    | x <- [0 .. 16]
    , y <- [0 .. 16]
    ]

dl :: Integer
dl =
  maximum
    [ m !! (x + 3) !! y * m !! (x + 2) !! (y + 1) * m !! (x + 1) !! (y + 2) *
    m !! x !! (y + 3)
    | x <- [0 .. 16]
    , y <- [0 .. 16]
    ]

main :: IO ()
main = print $ maximum [hm, vm, dr, dl]


-- 70600674

-- real 0m0,009s
-- user 0m0,003s
-- sys  0m0,005s