haskell problems 001 -> 006

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diff --git a/haskell/004-largest_palindrome_product.hs b/haskell/004-largest_palindrome_product.hs
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+-- Largest palindrome product
+
+-- Problem 4
+-- A palindromic number reads the same both ways.
+-- The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
+
+-- Find the largest palindrome made from the product of two 3-digit numbers.
+
+
+main = do
+    print (maximum [x * y | x <- [0..999], y <- [0..999], is_palindrome (x * y)])
+
+is_palindrome :: Int -> Bool
+is_palindrome x = all (\(y, z) -> y == z) $ zip (show x) (rev' $ show x)
+
+rev' :: [a] -> [a]
+rev' [] = []
+rev' (x:xs) = (rev' xs) ++ [x]