[Haskell-cafe] Timing pure functions?

[austin s]

Excerpts from Magnus Therning's message of Wed May 27 03:51:19 -0500 2009:
> Yesterday I spent about 5 minutes trying to time a single function in
> haskell (after having spent about 30 minutes on the timeit module in
> Python).  I found timeit[1] on Hackage but it only times an IO
> computation once, what I'd like to do is time a pure function several
> times.  Timing it once was no problem, passing `return $! myPureFunc`
> to `timeIt` did that[2].  My feeble attempt at collecting several
> timings failed though.
> 
>   import System.CPUTime
>   import qualified Codec.Binary.Base64 as B64
>   import System.IO
>   import qualified Data.ByteString as BS
>   import Control.Monad
> 
> 
>   timeIt times ioa = let
>           timeOnce = do
>               t1 <- getCPUTime
>               a <- ioa
>               t2 <- getCPUTime
>               let t = fromIntegral (t2-t1) * 1e-12
>               return t
>           in sequence $ take times $ repeat timeOnce
> 
>   main = do
>       fh <- openBinaryFile "/dev/urandom" ReadMode
>       d <- liftM BS.unpack $ BS.hGet fh 100000
>       t <- timeIt 10 $ return $! B64.encode d
>       print t
> 
> Running this on my machine produces the output
> [2.3331e-2,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0].  I.e. the first time
> the data is encoded, but the following 9 times it's not.
> 
> I suspect that it all comes from `B64.encode d` being pure, hence the
> encoding happens only once.  Now I _really_ want the encoding to
> happen 10 times, is there some easy way to achieve this?
> 
> /M
> 
> [1]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/timeit
> [2]:

Perhaps benchpress would be more to your liking:

  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/benchpress

Austin