[Haskell-cafe] Trouble finding exception source

[gwern0 at gmail.com]

On 2008.02.26 23:13:59 -0500, Denis Bueno <dbueno at gmail.com> scribbled 7.4K characters:
> Hi all,
>
> I've got some code crashing with "Prelude.foldr1: empty list".  In
> GHCi, the code uses too much memory (I kill it after it consumes 1GB)
> to be able to use :trace and :history, but I just found out about the
> -xc RTS option.  I tried that, and I get the following:
>
>     <GHC.List.CAF>dsat: Prelude.foldr1: empty list
>
> Now, manually going through GHC.List
> (http://haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-List.html)
> I only found one CAF, namely prel_list_str, at the bottom of the file.
>  However, it is late and I quite possibly missed something.  This CAF,
> of course, doesn't seem a likely culprit.  I also stumbled on some
> discussion of the explicit call stack
> (http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack/StackTraceExperience)
> which exemplifies the behavior I've found, but doesn't seem to suggest
> a way to fix it.
>
> I'm developing on GHC 6.8.2.  I've attached my code, the output of a
> cabal sdist, which requires parse-dimacs [0] and bitset [1] (both
> cabalised) to build.  If you build the executable (with profiling),
> you should see my behavior by running:
>
>     ./dist/build/dsat/dsat -verify +RTS -xc
>
> I know that the problem is somewhere in the "Backtracking" section, in
> the backJump function.  But I don't know where.
>
> Any help is appreciated.
>
> --
>                               Denis

Fortuitously, I recently came across a bunch of bioinformatics software in Haskell. One of the libraries was called 'interlude', and it claims to be able to give line locations for errors in the Prelude. I was intending to upload them all as a group once I'd finished, but you might be able to make use of it here.

You can find it here: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/interlude-0.1.1>.

If it does work out for you, be sure to let me know. I haven't run across any Prelude errors in my code since I installed it, so I haven't really tried it out.

--
gwern
brigand Investigation Firewalls Galil NTIS TDYC Yukon Morse Jazeera INR
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