Strange behavior in GHC-compiled code

[Mark Conway Wirt]

On Fri, May 25, 2012 at 05:53:52PM +0100, Malcolm Wallace wrote:

> Unless you show us the code, any answers will be guesses in the dark.
> Does your program use unsafePerformIO unsafely perhaps?  Or a version
> of a library that happens to have a known bug?

No unsafePerformIO's or IOrefs or the like. The code itself is
straight-forward (I think). It uses no external libraries -- just Data
and System as bundled.

One of the problems is that I don't know where in the code the problem may
be arising -- the code is about 1200 lines, so it's not really practical
to post it!

(I'm starting to think that this issue may not be related to
Haskell, as the problem arises so inconsistently -- sometimes the
code runs, sometimes it bombs out early. I haven't rebooted the
computer in a month or so, maybe it's time.)

I guess what I'm asking is: what strategies should I be employing for
debugging the problem? If the problem is with an array, for example,
"error in array index" doesn't give me much to go on if I don't know
which array may be the problem. Should I be trying to reproduce the 
problem in ghci's debugger, for example? Will that give me more context?

--Mark