Renaming PreImages... functions as PreImages...NC : GAP PR#5073

[cdwensley]

PreImagesRepresetnative, PreImages, PreImagesSet and PreImagesElm can all return incorrect results when the element(s) supplied are not in the range of the map.
This situation has been discussed in GAP issue #4809.
To rectify the situation the plan is to have NC versions of these four operations and to add tests to the non-NC versions.
The procedure to be adopted is as follows.
(1) Rename the four operations by adding 'NC' to their names, and then declare the original operations as synonyms of these. PR #5073 addresses this.
(2) Ask package authors/maintainers to convert all their calls to these functions to the NC versions (unless there is good reason not to do so).
A clause added to init.g ensures the package works in older versions of GAP.
(3) Once all the packages have been updated, add tests to the non-NC versions of the operations.

No progress has been made on this since February, but now seems a good time to continue with stage (2).
No PR is offered to Semigroups at the moment because it is not clear what to do.
In attributes/homomorph.gi there are two methods implemented, and both of these apply tests, so should clearly not be converted to NC.
On the other hand, in attributes/isorms.gi there are two new methods implemented which do not do tests, so perhaps should be converted to NC.
Apart from these methods, there are just a few calls to PreImagesRepresentative.
How would the package authors like to proceed?

[james-d-mitchell]

Thanks @cdwensley I’m happy to fix this thanks for the report!

[cdwensley]

That's great. Tried three PRs today for various packages but suspect I'll hear nothing from the other two! This thing has dragged on far too long, which is entirely my fault, but a good push now might result in some progress. Maybe you can help with my query on Slack?

[cdwensley]

This is clearly nowhere near the top of your TODO list, which is very understandable. So I will make a start on a PR - tell me if you want me to stop!

[cdwensley]

But that's only if I can manage to compile Semigroups! I can get ./configure to work, but not make:
christopherwensley@Christophers-iMac semigroups % ./configure --with-gaproot=/Users/christopherwensley/gap/gap-4.12.2
...
lots of output
...
christopherwensley@Christophers-iMac semigroups % make
make: *** No rule to make target Makefile.am', needed by Makefile.in'. Stop.

This is on an iMac less than two years old, so GCC and clang (whatever they are) should be OK.
And I am working with a version of Semigroups cloned from GitHub.

[james-d-mitchell]

I'll welcome a pr with these changes! You need to ./autogen.sh in the semi groups directory before running configure.

[cdwensley]

Yes, that was done first. The situation today is that 5.2.0 compiles just fine on my system, but not the GitHub version.
So I am wondering if there is something missing from this website.
Anyway, I can make a start on a PR using the 5.2.0 version as a check.
Here is today's log:
christopherwensley@Christophers-iMac semigroups % ./autogen.sh
++ dirname ./autogen.sh

• autoreconf -vif .
  autoreconf: export WARNINGS=
  autoreconf: Entering directory '.'
  autoreconf: configure.ac: not using Gettext
  autoreconf: running: aclocal --force
  autoreconf: configure.ac: tracing
  autoreconf: configure.ac: adding subdirectory libsemigroups to autoreconf
  autoreconf: Entering directory 'libsemigroups'
  autoreconf: configure.ac: not using Gettext
  autoreconf: running: aclocal --force -I m4
  autoreconf: configure.ac: tracing
  autoreconf: running: glibtoolize --copy --force
  glibtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, 'config'.
  glibtoolize: copying file 'config/ltmain.sh'
  glibtoolize: putting macros in AC_CONFIG_MACRO_DIRS, 'm4'.
  glibtoolize: copying file 'm4/libtool.m4'
  glibtoolize: copying file 'm4/ltoptions.m4'
  glibtoolize: copying file 'm4/ltsugar.m4'
  glibtoolize: copying file 'm4/ltversion.m4'
  glibtoolize: copying file 'm4/lt~obsolete.m4'
  autoreconf: configure.ac: not using Intltool
  autoreconf: configure.ac: not using Gtkdoc
  autoreconf: running: aclocal --force -I m4
  autoreconf: running: /opt/homebrew/Cellar/autoconf/2.71/bin/autoconf --force
  autoreconf: running: /opt/homebrew/Cellar/autoconf/2.71/bin/autoheader --force
  autoreconf: running: automake --add-missing --copy --force-missing
  configure.ac:20: installing 'config/compile'
  configure.ac:18: installing 'config/missing'
  Makefile.am: installing 'config/depcomp'
  autoreconf: Leaving directory 'libsemigroups'
  autoreconf: configure.ac: not using Libtool
  autoreconf: configure.ac: not using Intltool
  autoreconf: configure.ac: not using Gtkdoc
  autoreconf: running: /opt/homebrew/Cellar/autoconf/2.71/bin/autoconf --force
  configure.ac:46: error: possibly undefined macro: AC_SUBST
  If this token and others are legitimate, please use m4_pattern_allow.
  See the Autoconf documentation.
  autoreconf: error: /opt/homebrew/Cellar/autoconf/2.71/bin/autoconf failed with exit status: 1
  christopherwensley@Christophers-iMac semigroups % ./configure -with-gaproot=/Users/christopherwensley/gap/gap-4.12.2
  configure: error: cannot find required auxiliary files: config.guess config.sub

[cdwensley]

PR #965 created : approval required to run the tests.