I would like to be able to retract and assert facts dynamically for the procedure location:
location(egg, duck_pen).
Based on advice online (including No permission to modify static procedure), I've tried adding each of the following to my source code, which otherwise contains only the above assertion:
dynamic location/2.
dynamic(location/2).
dynamic(location)/2.
The first two versions give me this error at compile-time (when loaded into SWI-Prolog):
No permission to redefine built-in predicate `(dynamic)/1'
Use :- redefine_system_predicate(+Head) if redefinition is intended
The last version does not give me an error at compile-time, but, whether I put it at the beginning or end of the file, I get an error when I try retracting my fact:
?- retract(location(egg,duck_pen)).
ERROR: retract/1: No permission to modify static procedure `location/2'
I am using SWI-Prolog version 6.6.5.
