-- greatest product of 13 adjacent digits in a large number

main = print getProblem8Value

getProblem8Value :: Integer
getProblem8Value = getLargestProductOf13Digits largeNum

getLargestProductOf13Digits :: [Integer] -> Integer
getLargestProductOf13Digits list@(a:b:c:d:e:f:g:h:i:j:k:l:m:rest) = max (a*b*c*d*e*f*g*h*i*j*k*l*m) (getLargestProductOf13Digits next)
    where (_:next) = list
getLargestProductOf13Digits _ = 0

largeNum :: [Integer]
largeNum = map (read . (\x -> [x])) (concat [
    "73167176531330624919225119674426574742355349194934",
    "96983520312774506326239578318016984801869478851843",
    "85861560789112949495459501737958331952853208805511",
    "12540698747158523863050715693290963295227443043557",
    "66896648950445244523161731856403098711121722383113",
    "62229893423380308135336276614282806444486645238749",
    "30358907296290491560440772390713810515859307960866",
    "70172427121883998797908792274921901699720888093776",
    "65727333001053367881220235421809751254540594752243",
    "52584907711670556013604839586446706324415722155397",
    "53697817977846174064955149290862569321978468622482",
    "83972241375657056057490261407972968652414535100474",
    "82166370484403199890008895243450658541227588666881",
    "16427171479924442928230863465674813919123162824586",
    "17866458359124566529476545682848912883142607690042",
    "24219022671055626321111109370544217506941658960408",
    "07198403850962455444362981230987879927244284909188",
    "84580156166097919133875499200524063689912560717606",
    "05886116467109405077541002256983155200055935729725",
    "71636269561882670428252483600823257530420752963450" ])