gistfile1.hs

module Main where

import System.Environment

import Data.ByteString.Char8 as B
import Data.Map              as M
import Data.List             as L

import Data.Maybe


main = do
  let known = M.fromList [ (B.pack "foo", 0)
                         , (B.pack "bar", 1)
                         ]
  fname <- L.head  `fmap` getArgs
  ls    <- B.lines `fmap` B.readFile fname
  -- find all lines that exist as a key in known
  print $ L.reverse $ L.filter (isJust . (flip M.lookup) known) ls