[Haskell-cafe] Timing execution of individual functions in ghci?

Magnus Therning magnus at therning.org
Thu Oct 23 14:04:45 UTC 2014

On Wed, Oct 22, 2014 at 12:48:53PM +0200, Daniel Trstenjak wrote:
> Hi Magnus,
>> When playing around with various implementations of a single
>> function it would be nice to time the execution. Is there some way
>> to do that easily from within GHCi?
> ghci normally only interprets your code, without much optimizations,
> so your timings might be quite misleading.

Well, it might be enough to confirm or disprove intuitions about time
complexity of an implementation; is it O(n) or O(n^2)?  And that's
really what I'd like to see at a first step.

Given that all I'm interested in is relative timings it might even be
enough to do a rough comparison of two implementations too.

>> Or am I forced to look to criterion for that?
> I think so, if you want to trust your timings.

It's just a bit too much ceremony when all I want is to confirm that
"inserting in reversed order followed by a `reverse`" has less time
complexity than "repeated appending."

Of course the only way to get something I can take to the bank is
using criterion.


Magnus Therning                      OpenPGP: 0xAB4DFBA4 
email: magnus at therning.org   jabber: magnus at therning.org
twitter: magthe               http://therning.org/magnus

Heuristic is an algorithm in a clown suit. It’s less predictable, it’s more
fun, and it comes without a 30-day, money-back guarantee.
     -- Steve McConnell, Code Complete 
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