I'd like to use the PceEmacs editor but whenever I use the command emacs., I'm met with the error code
ERROR: Undefined procedure: emacs/0 (DWIM could not correct goal). The normal built in commands seem to work as normal so I don't know if I'm just using the emacs command wrong.
You have probably not installed everything. You need to tell us what operating system you are using, how you installed SWI-Prolog, and stuff like that.
For example, in an installation without PCE, you won't have PceEmacs. On a machine on which I purposefully don't have PCE, I see the exact same thing as you do:
$ swipl
Welcome to SWI-Prolog (threaded, 64 bits, version 8.1.8-43-gb0168ea4a-DIRTY)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.
For online help and background, visit http://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).
?- emacs.
ERROR: Unknown procedure: emacs/0 (DWIM could not correct goal)
This is because I have, in my build script:
cmake -G Ninja -DSWIPL_PACKAGES_X=OFF ...