gistfile1.hs

import Data.List (sort)

problem_four :: Int
problem_four =
    head . reverse . sort $
         filter (>0) $ concat $ map (\x ->
                                         map( \y -> fix x y ) nx
                                    ) nx
 where
   nx :: [ Int ]
   nx = [ 100 .. 999 ]

   is_pal :: Int -> Int
   is_pal x =
     case ( show x ) == ( reverse $ show x ) of
       True ->
         x
       _ -> 0
   fix :: Int -> Int -> Int
   fix x y =
     is_pal $ x * y