# Timing computations

Revision as of 03:14, 27 January 2010 by DonStewart (talk | contribs)

Timing an IO computation -- very basic approach. For a full featured, statistically sound benchmarking system, see the criterion package.

```
import Text.Printf
import Control.Exception
import System.CPUTime
time :: IO t -> IO t
time a = do
start <- getCPUTime
v <- a
end <- getCPUTime
let diff = (fromIntegral (end - start)) / (10^12)
printf "Computation time: %0.3f sec\n" (diff :: Double)
return v
main = do
putStrLn "Starting..."
time $ product [1..10000] `seq` return ()
putStrLn "Done."
```

And running this.

```
$ runhaskell A.hs
Starting...
Computation time: 1.141 sec
Done.
```

See also Timing out computations and Timing computation in cycles.

Timing a pure computation:

```
import Text.Printf
import Control.Exception
import System.CPUTime
import Control.Parallel.Strategies
import Control.Monad
import System.Environment
lim :: Int
lim = 10^6
time :: (Num t, NFData t) => t -> IO ()
time y = do
start <- getCPUTime
replicateM_ lim $ do
x <- evaluate $ 1 + y
rnf x `seq` return ()
end <- getCPUTime
let diff = (fromIntegral (end - start)) / (10^12)
printf "Computation time: %0.9f sec\n" (diff :: Double)
printf "Individual time: %0.9f sec\n" (diff / fromIntegral lim :: Double)
return ()
main = do
[n] <- getArgs
let y = read n
putStrLn "Starting..."
time (y :: Int)
putStrLn "Done."
```