On Fri, Oct 19, 2007 at 02:09:01 +1000, Matthew Brecknell wrote: >Magnus Therning: >> Just out of curiosity, how would I go about finding this myself? >> (Ideally it'd be an answer other than "read the source for the libraries >> you are using". :-) > >Well, I can at least try to expand a little on "read the source". :-) > >You'll first need a solid understanding of lazy evaluation in the >context of pure computations. Read about normal evaluation order, WHNF >(weak head normal form), and which contexts force WHNF. Use pen and >paper to manually derive the evaluation order for some pure >computations of your choice (folds over infinite lists would be a good >start). Experiment with "seq". Experiment with the various causes of >stack overflows. Next, understand that while the IO monad is quite >strict about sequencing actions, its "return" is not strict in its >argument. Observe that the combinators in Control.Monad generally do >not force returned computations. Browse the source of GHC's IO library >to understand how it sequences IO actions. Read the source for >unsafePerformIO and unsafeInterleaveIO to understand how and for what >purposes they allow you to break that sequencing. Next, read the source >for hGetContents. After all that, you should be a little better >equipped to diagnose problems with lazy IO!
I'll certainly try to look into all of that. However, I suspect your suggestion doesn't scale very well. On my original code it's easy, it was less than 10 lines, but how do I know where to start looking if it's a program of 100 lines, or 1000 lines? The problem could occur in an updated library that I just use... Well you get the idea :-) I can use profiling to find where time and space is spent. But what about other finite resources that my program uses, such as file handles? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus．therning＠gmail．com http://therning.org/magnus
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