Profile something by its stdout line by line.

gistfile1.hs

import Control.Applicative
import Control.Monad.Loops
import Data.Time.Clock.POSIX
import System.IO

main :: IO ()
main = do
    stampedLines <- whileM (not <$> isEOF) $ do
        l <- getLine
        t <- getPOSIXTime
        putStrLn l
        return (t, l)
    tEnd <- getPOSIXTime
    let timedLines = zipWith (\(t0, s0) t1 -> (t1 - t0, s0))
                             stampedLines
                             (tail (fmap fst stampedLines) ++ [tEnd])
    putStrLn "\n-----------------\n"
    mapM_ (\(t, s) -> putStrLn (concat [show t, "\t", s]))
          timedLines