[Haskell-beginners] Forcing output of show

Hello, Apologies for this newbie question. I have a test function: testLearnRules train = do h <- IO.openFile train IO.ReadMode c <- IO.hGetContents h let proposedRules = instRules $ words c let rs = take 10 $ M.assocs proposedRules let _ = show rs -- let _ = length rs return () I realize that nothing is executed due to Haskell's lazy evaluation. How can I force show to print something to the screen? Appreciate any pointers, TIA, Hugo F.