How to get a program's running time in Haskell

Question

How can I go about getting a program's running time through system time functions in Haskell? I would like to measure the execution time of a whole program and/or an individual function.

Answer 1

1) If you want to benchmark something, use the criterion package.

2) If you want to time a function and are positive you have controlled for laziness as needed, then just use Data.Time.getCurrentTime from the time package.:

import Data.Time
...
   start <- getCurrentTime
   runOperation
   stop <- getCurrentTime
   print $ diffUTCTime stop start

A slicker packaging of the above pattern can be found in the timeit package.

3) If you actually want the running time of a program that just happens to be written in Haskell then use your systems time utility. For most POSIX systems (Mac, Linux) just run:

$ time ./SomeProgram

And it will report user, wall, and system time.

Answer 2

Assuming you don't just want to measure the total running time of your program, like so:

 $ time ./A

Then you can time a computation a number of ways in Haskell:

• Basic timing (e.g. as in the timeit package)
• Timing in cycles

For more statistically sound measurement, consider

• The Criterion package.

Finally, in all cases, you need to think about lazy evaluation: do you want to measure the cost of fully evaluating whatever data you produce, or just to its outermost constructor?

Answer 3

:set +s is really neat if use ghci, otherwise you can use Criterion.Measurement, see my answer to another question with example.

Answer 4

I'm not sure how accurate it is, but using :set +s in ghci will show the time and space used for subsequent computations.