Thanks for the info, very interesting. Yes, I'm using GHCi, and I'm using forkOS, and I'm using OpenGL...

Since I'm used to write heavily multi-threaded/multi-core code in imperative languages, I would like to understand more about the existing execution models, and those "black holes"... Understanding the low-level details helps a lot for me.

Actually the problem was caused by (yet another) strict pattern match in my code, which should have been lazy. I find it strange that this would cause 0% CPU time... But then again I don't understand the details of how GHCi/GHC works. I did read the book "Modern Compiler Design" (http://www.cs.vu.nl/~dick/MCD.html) which implements a basic Haskell interpreter & compiler, so I got an introduction.

Anyway, it's a very good learning experience for me to "redo" FRP from scratch, as I encounter all pitfalls (such as the need for memoization when using recursive streams, the need for lazy pattern matching, the space leaks sneaking up on you, etc). Once I get to understand these in detail, I'll try to re-read the existing papers on FRP, which I hardly understood initially :-)

Thanks,
Peter

Stefan O'Rear wrote:

On Wed, Sep 19, 2007 at 10:24:24PM +0100, Neil Mitchell wrote:

Hi Peter,

 So I grabbed ghc-6.7.20070824 (=the latest one for Windows I could find)
and the "extra-libs", compiled and installed the GLUT package (which I
needed), but when I compile my library, I get

     Could not find module `Data.Map':
       it is a member of package containers-0.1, which is hidden

All dependencies etc. have changed when going to 6.7/6.8 - you are
probably better off using 6.6.1 for now.

I also don't think that the debugger will help you track down infinite
loop style errors. You might be better off posting the code and asking
for help.


You said 0% CPU.  That's *very* important.  It means that you are using
the threaded runtime (GHCi?), and that you triggered a blackhole.  You
should be able to handle this by compiling your program with -prof (do
*not* use -threaded!), and running with +RTS -xc.  With luck, that will
give you a backtrace to the infinite loop.

PS. blackholes are a serious dark corner of GHC's execution model,
chances are better than even that if you try to use the debugger for
this you will discover a new and (for you) crippling bug.  I wouldn't
recommend it.

Stefan