Memo.hs

{- 
you need the memoize cabal package to use this.
http://hackage.haskell.org/package/memoize-0.3
-}

import System.IO.Unsafe
import System.Posix.Files
import System.Posix.Types
import Data.Function.Memoize
import Debug.Trace

mtime' :: String -> EpochTime
mtime' = (trace "now executing") . modificationTime . unsafePerformIO . getFileStatus

mtime = memoize mtime'

*Main> mtime "Memo.hs"
now executing
1360829955
*Main> mtime "Memo.hs"
1360829955