How to get a program's running time in Haskell

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.

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?

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: