I haven’t used Prolog for some years and have just build the most recent version.
I noticed that XPCE was missing and after a quick search I found packages-xpce. README.md tells that instructions for building XPCE can be found in INSTALL.md but that file is missing?
Is XPCE still used or is there an alternative? Where can I find build instructions?
And if you really want to use xpce as such yourself, use
:- use_module(library(pce)).
If you plan to do so it may also be wise to disable xpce from running in its own thread using this before you load the library.
:- set_prolog_flag(xpce_threaded, false).
By default, the IDE tools are using xpce and allow xpce to run in a thread pce. That allows editing, inspecting threads, etc. while your application runs. Keeping xpce in a thread does does require using stuff like in_pce_thread/1 to execute goals in the pce thread.