I want to add a new predicate (<--)/2 similar to (-->)/2 or (:-)/2.
I use it in this library with the term_expansion/2.
Unfortunately, the built-in prolog editor does not treat this predicate as a built-in (-->)/2.
The (<--)/2 predicate is colored red, the left atom is not bold and the targets on the right have no automatic indentation (screenshot below).
How to fix it?
To get the highlighting to work you need to add rules for the multifile hooks of library(prolog_colour). The indentation requires probably changes to the prolog mode in the builtin editor. Fire it up and run ?- edit(prolog_mode). It is all possible. Requires a bit of work though. For the indentation it may require adding hooks to the defined Prolog mode such that user code can be added to support alternative clause definitions.