Dealing with Calling nb_current with undefined global invokes user:exception hook · Issue #868 · SWI-Prolog/swipl-devel · GitHub, I decided to have a special no value in global variables. This would also allow us that backtracking which takes us back to before the first b_setval/2 to delete the variable rather than binding it to
I’ve implemented this and, except for having to adjust the tests that verify resetting to
 this doesn’t seem to have any consequences for any of the other tests.
Deleting is obviously cleaner than resetting to
. Is it worth the incompatibilities that may result from it?