[Haskell-cafe] Obscure weirdness

Andrew Coppin andrewcoppin at btinternet.com
Sat Jun 20 13:34:12 EDT 2009

Alexander Dunlap wrote:
> On Sat, Jun 20, 2009 at 8:29 AM, Andrew Coppin
> <andrewcoppin at btinternet.com> wrote:
>> OK, so here's an interesting problem...
>> I've been coding away all day, but now my program is doing something slightly weird. For a specific input, it summarily terminates. The registered exception handler does not fire. There is no output to stdout or stderr indicating what the problem is. It just *stops* half way through the printout.
>> Weirder: If I run it in GHCi, then GHCi itself terminates. (I didn't think you could *do* that!)
> I think you'll need to provide a bit more detail about what you're
> doing in order for anyone to have anything to go off of. If you can
> link to the source, that would help, or even give a summary of what
> you're trying to do.

The program takes some text, parses it as a lambda calculus expression, 
and prints it out again. Except, somewhere during the variable 
uniqueness pass, the program just halts. For no defined reason.

As you can see, nothing remotely unusual for a Haskell program to be 
doing. And yet, the result is very unusual. (I.e., halting part-way 
through some pure code without throwing an exception.)

Given that it doesn't appear to be a known bug (presumably somebody 
would have said something by now if it was...), I think I'm going to try 
upgrading GHC anyway, just for arguments' sake, and see if that fixes it.

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