gprolog toplevel fails on basic example (fixed upstream?)

[Cedric Ware]

Hello,

In Ubuntu 17.04 (Zesty), with gprolog 1.4.5-4.1, the toplevel interpreter fails to execute valid code, including this basic example copied from the manual:

krakatoa ~ % gprolog
GNU Prolog 1.4.5 (64 bits)
Compiled Feb 5 2017, 10:30:08 with gcc
By Daniel Diaz
Copyright (C) 1999-2016 Daniel Diaz
| ?- [user].
compiling user for byte code...
even(0).
even(s(s(X))) :- even(X).

user compiled, 2 lines read - 326 bytes written, 12353 ms

(3 ms) yes
| ?- even(X).

X = 0 ? ;
uncaught exception: error(existence_error(procedure,even/0),even/0)
| ?-

The same example works with all other versions of gprolog I tested: the older 1.3.0-6.1 in Xenial; the stable version 1.4.4 downloaded from http://www.gprolog.org/ (with commit cc8249 applied manually to fix compilation); as well as a freshly-cloned git repository from https://git.code.sf.net/p/gprolog/code . For instance:

krakatoa ~ % export PATH=/opt/gprolog-1.4.4/bin:$PATH
krakatoa ~ % gprolog
GNU Prolog 1.4.4 (64 bits)
Compiled Aug 17 2017, 12:18:48 with gcc
By Daniel Diaz
Copyright (C) 1999-2013 Daniel Diaz
| ?- [user].
compiling user for byte code...
even(0).
even(s(s(X))) :- even(X).

user compiled, 3 lines read - 321 bytes written, 3627 ms

yes
| ?- even(X).

X = 0 ? ;

X = s(s(0)) ? ;

X = s(s(s(s(0)))) ? ;

X = s(s(s(s(s(s(0)))))) ?

yes
| ?-

I believe the bug was introduced and fixed sometime between 1.4.4 and the current code in git. It looks related to these messages in the users-prolog mailing list. No fix was subsequently announced, but the current code works.
http://<email address hidden>/msg01032.html
http://<email address hidden>/msg01033.html

This bug makes Zesty's gprolog package unusable. Could you please update it?

Thanks in advance,
Cedric Ware.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Ian Lewis (ijl20)]

Just to emphasize, this bug means that the Prolog programming language is realistically unavailable in all Ubuntu versions since 16.04. The 1.4.5-4.1 build of gprolog has this fundamental crippling bug as reported by the OP - even the most basic Prolog programs will not run - and unfortunately the 1.4.4 make from source also throws up a number of compile errors so it is a specialist job to get that code installed.

[Ian Lewis (ijl20)]

Here's the simplest failing test example I could come up with, which is close to 'hello world' for prolog :

$ prolog
GNU Prolog 1.4.5 (64 bits)
Compiled Feb 5 2017, 10:30:08 with gcc
By Daniel Diaz
Copyright (C) 1999-2016 Daniel Diaz
| ?- [user].
compiling user for byte code...
p :- q(a).
q(a).

user compiled, 2 lines read - 294 bytes written, 13418 ms

yes
| ?- p.
uncaught exception: error(existence_error(procedure,q/0),p/0)
| ?-

On the query "?- p." gprolog should return with "yes", not the exception.

[Cedric Ware (cedric.ware)]

Hello,

Thanks for your comment, Ian, and for reminding me again of this bug.

If it can help, I'm attaching a patch that lets the stable gprolog-1.4.4 compile with gcc 6.

OTOH, I'm not sure that this is actually the right place to report bugs, because I suspect Ubuntu uses the Debian package more or less as-is. Correct me if I'm wrong. As it happens, the bug has been reported in Debian (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=861027), and has prevented gprolog to be included in recent stable releases, I guess.

I submitted a follow-up to that bug, wait and see.

Best regards,
Cedric Ware.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "Patch against previous version of gprolog (latest stable)." seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Ian Lewis (ijl20)]

thanks - I can confirm gprolog 1.4.4 compiles from source ok on Ubuntu 18.04, and runs without this bug. I wasn't expecting the 1.4.5 bugfix to appear here but thought it would make sense to package 1.4.4 rather than 1.4.5

[Huan Zhang (victzhang)]

I can confirm this bug still exists on Ubuntu 18.04 as of today.