This is a simplified version of an issue I'm running into when timing some functions. In this example, the first putStr inside the replicateM_ takes far longer than subsequent putStrs. If I add in a putStr at the top (the commented line), each iteration takes the same. (Though I presume I just shifted the long execution to the putStr on top). The same thing happens on the first iterations of a function when I need to evaluate some state, or deepseq some value. putStr was just a simpler version that still showed the same issue. Relevant code: http://lpaste.net/136250 What's going on here? Thanks! import Control.Monadimport Data.Time.Clock main :: IO ()main = do -- putStr "" replicateM_ 5 $ do t1 <- getCurrentTime putStr "" t2 <- getCurrentTime print . round $ 1000 * 1000 * diffUTCTime t2 t1 {- Sample output: 49 1 1 1 2 -}