Path: utzoo!mnetor!tmsoft!torsqnt!hybrid!scifi!bywater!uunet!cs.utexas.edu!bradley
From: bradley@cs.utexas.edu (Bradley L. Richards)
Newsgroups: comp.lang.prolog
Subject: Quintus Prolog problem
Message-ID: <310@thunderbird.cs.utexas.edu>
Date: 10 Feb 91 21:08:22 GMT
Organization: Dept of Computer Sciences, UTexas, Austin
Lines: 43

I've run into a very odd problem with Quintus Prolog--perhaps someone else has
run into this problem and determined the cause of it.  My program is generating
an endless stream of segmentation fault messages, for no apparent reason.  An
editted excerpt from a trace follows:

.
.
.
   (154052) 10 Call: ifoil:ifoil_find_best_ante(...) ? s
 > (154052) 10 Exit: ifoil:ifoil_find_best_ante(...) ?
   (156657) 10 Call (built_in): retract(data:ifoil_ante(_12868, ...)) ?
   (156657) 10 Exit (built_in): retract(data:ifoil_ante(-1, ...)) ?
   (156660) 10 Call (built_in): -1>=0 ?
   (156660) 10 Fail (built_in): -1>=0 ?
   (156657) 10 Redo (built_in): retract(data:ifoil_ante(-1, ...)) ?
[ Internal error (signal): Segmentation fault ]
[ Internal error (signal): Segmentation fault ]
[ Internal error (signal): Segmentation fault ]
.
.
.
ad infinitum

The redo of the retract should fail, since there are no more matching clauses.
In fact, it *used* to fail (and this problem did not arise), until I made some
changes in what should have been unrelated parts of the program.

The only recourse at this point is to interrupt with ^C and exit Prolog.  Even
an abort doesn't help--the error messages just keep coming.  The idea that
Prolog is out of memory turns out not to be the case--at this point it is
using about 1.5M out of a 15M limit (on a machine with much more than that
available).

Any ideas on causes or cures?

Bradley

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 Bradley L. Richards             "The abandonment of formal mathematics
 bradley@cs.utexas.edu           is an extremely popular thing to do in
 uucp:  cs.utexas.edu!bradley    computer science."
                                                    Dr. Robert Boyer, NACLP-90
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