haskell problems 007 -> 010

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diff --git a/haskell/008-largest_product_in_a_series.hs b/haskell/008-largest_product_in_a_series.hs
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+-- Largest product in a series
+
+-- Problem 8
+-- The four adjacent digits in the 1000-digit number that have
+-- the greatest product are 9 × 9 × 8 × 9 = 5832.
+
+-- 73167176531330624919225119674426574742355349194934
+-- 96983520312774506326239578318016984801869478851843
+-- 85861560789112949495459501737958331952853208805511
+-- 12540698747158523863050715693290963295227443043557
+-- 66896648950445244523161731856403098711121722383113
+-- 62229893423380308135336276614282806444486645238749
+-- 30358907296290491560440772390713810515859307960866
+-- 70172427121883998797908792274921901699720888093776
+-- 65727333001053367881220235421809751254540594752243
+-- 52584907711670556013604839586446706324415722155397
+-- 53697817977846174064955149290862569321978468622482
+-- 83972241375657056057490261407972968652414535100474
+-- 82166370484403199890008895243450658541227588666881
+-- 16427171479924442928230863465674813919123162824586
+-- 17866458359124566529476545682848912883142607690042
+-- 24219022671055626321111109370544217506941658960408
+-- 07198403850962455444362981230987879927244284909188
+-- 84580156166097919133875499200524063689912560717606
+-- 05886116467109405077541002256983155200055935729725
+-- 71636269561882670428252483600823257530420752963450
+
+-- Find the thirteen adjacent digits in the 1000-digit number that have
+-- the greatest product. What is the value of this product?
+
+
+import Data.Char
+
+main = do
+    print (largest_adj_product big_nb)
+
+largest_adj_product :: String -> Int
+largest_adj_product str = find_max str 0
+    where find_max s m
+            | length s < 13 = m
+            | (first_prod s) > m = find_max (tail s) (first_prod s)
+            | otherwise = find_max (tail s) m
+          first_prod striped = foldl (\acc x -> acc * (digitToInt x)) 1 (take 13 striped)
+
+big_nb = "73167176531330624919225119674426574742355349194934\
+          \96983520312774506326239578318016984801869478851843\
+          \85861560789112949495459501737958331952853208805511\
+          \12540698747158523863050715693290963295227443043557\
+          \66896648950445244523161731856403098711121722383113\
+          \62229893423380308135336276614282806444486645238749\
+          \30358907296290491560440772390713810515859307960866\
+          \70172427121883998797908792274921901699720888093776\
+          \65727333001053367881220235421809751254540594752243\
+          \52584907711670556013604839586446706324415722155397\
+          \53697817977846174064955149290862569321978468622482\
+          \83972241375657056057490261407972968652414535100474\
+          \82166370484403199890008895243450658541227588666881\
+          \16427171479924442928230863465674813919123162824586\
+          \17866458359124566529476545682848912883142607690042\
+          \24219022671055626321111109370544217506941658960408\
+          \07198403850962455444362981230987879927244284909188\
+          \84580156166097919133875499200524063689912560717606\
+          \05886116467109405077541002256983155200055935729725\
+          \71636269561882670428252483600823257530420752963450"