# A new bug in my old code? **URL:** \ **Category:** Help!\ **Tags:** bug\ **Created:** [August 30, 2026, 2:13pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804 "2026-08-30T14:13:27Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [August 30, 2026, 2:13pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/1 "2026-08-30T14:13:27Z")
I’m using: SWI-Prolog version 10.0.2. I want the code to: retract all dynamic predicates that are not built-in. But what I’m getting after cleanup each time I consult a file is: ERROR: Domain error: `file_type’ expected, found `prolog’. My code looks like this: ```prolog cleanup :- forall(dynamic_not_built_in(X),retractall(X)). dynamic_not_built_in(X) :- predicate_property(X,dynamic), \+predicate_property(X,built_in). ``` Call the above program mwe.pl, consult it and run cleanup. Then consult it again and get the ERROR above. Code like this has never given any problem in versions \< 9. From 9 on I get this behaviour. I suspect cleanup now retracts too much, perhaps an essential dynamic predicate which is not a built-in. Any help is highly appreciated! Marc ---
**Author:** ![Olopierpa](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/olopierpa/32/6855_2.png) [@Olopierpa](https://swi-prolog.discourse.group/u/Olopierpa)\ **Post date:** [August 30, 2026, 3:27pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/2 "2026-08-30T15:27:49Z")
> I suspect cleanup now retracts too much, You can easily check this hypotesis. In cleanup change retractall to writeln, and check whether the result looks reasonable. ---
**Author:** ![brebs](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@brebs](https://swi-prolog.discourse.group/u/brebs)\ **Post date:** [August 30, 2026, 4:20pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/3 "2026-08-30T16:20:54Z")
> [@Marc](#): > > ```prolog > predicate_property(X,dynamic), > \+predicate_property(X,built_in) > > ``` There is no overlap, so that will not filter as intended: ```prolog Welcome to SWI-Prolog (threaded, 64 bits, version 10.0.2) 101 ?- predicate_property(X, dynamic), predicate_property(X, built_in). false. ``` ---
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [August 30, 2026, 4:32pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/4 "2026-08-30T16:32:12Z")
Good suggestion, see the list below. I would have expected all of these are built-in. I guess the last one is the culprit. 61 ?- cleanup. prolog\_load\_file(\_7456,\_7458) portray(\_7456) expand\_answer(\_7456,\_7458) resource(\_7456,\_7458) exception(\_7456,\_7458,\_7460) term\_expansion(\_7456,\_7458) goal\_expansion(\_7456,\_7458,\_7460,\_7462) term\_expansion(\_7456,\_7458,\_7460,\_7462) resource(\_7456,\_7458,\_7460) file\_search\_path(\_7456,\_7458) goal\_expansion(\_7456,\_7458) expand\_query(\_7456,\_7458,\_7460,\_7462) message\_hook(\_7456,\_7458,\_7460) thread\_message\_hook(\_7456,\_7458,\_7460) library\_directory(\_7456) prolog\_file\_type(\_7456,\_7458) true. ---
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [August 30, 2026, 4:47pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/5 "2026-08-30T16:47:00Z")
But something must have changed. I seem to remember (but the program is 20y old) that it was necessary to exclude built-in predicates in those days: ````prolog ```Welcome to SWI-Prolog (threaded, 64 bits, version 8.0.3) 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). ?- cleanup. prolog_exception_hook(_7210,_7212,_7214,_7216) thread_message_hook(_7210,_7212,_7214) true. ?- [mwe]. true. ```` All these were built-in in version 8: ````prolog ``` ?- predicate_property(X,dynamic),predicate_property(X,built_in). X = prolog_event_hook(_7564) ; X = file_search_path(_7564, _7566) ; X = term_expansion(_7564, _7566) ; X = resource(_7564, _7566, _7568) ; X = prolog_file_type(_7564, _7566) ; X = goal_expansion(_7564, _7566) ; X = goal_expansion(_7564, _7566, _7568, _7570) ; X = portray(_7564) ; X = term_expansion(_7564, _7566, _7568, _7570) ; X = expand_query(_7564, _7566, _7568, _7570) ; X = expand_answer(_7564, _7566) ; X = message_hook(_7564, _7566, _7568) ; X = library_directory(_7564) ; X = prolog_load_file(_7564, _7566) ; X = resource(_7564, _7566) ;X = exception(_7564, _7566, _7568) ; false. ```` ---
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [August 30, 2026, 4:56pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/6 "2026-08-30T16:56:44Z")
In conclusion: from version 8 to version 10 the number of system-like predicates that are dynamic (but not built-in) increased substantially. My problem is now: how to discriminate in a robust way between user-defined dynamic predicates and all other dynamic predicates? ---
**Author:** ![Olopierpa](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/olopierpa/32/6855_2.png) [@Olopierpa](https://swi-prolog.discourse.group/u/Olopierpa)\ **Post date:** [August 30, 2026, 5:45pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/7 "2026-08-30T17:45:13Z")
maybe you can discriminate based on file of origin: > ```prolog > predicate_property(P,dynamic), > predicate_property(P,file(F)), > \+ sub_atom(F,_,_,_,'/swipl/library/'), > \+ sub_atom(F,_,_,_,'/swipl/boot/'). > > ``` if it has these in the name probably is not a user defined one. Not 100% safe, but may be a stopgap. ---
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [August 31, 2026, 1:58pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/8 "2026-08-31T13:58:56Z")
Appreciated the help, and tried it. However, on my platform (LM22.3) the substring /swipl/ should be /swi-prolog/, so I’m afraid it’s very fragile. For the moment I’m just going to exclude `prolog_file_type` from the retract of dynamic predicates. Hopefully a little more robust, but again a stop-gap. The better solution would be to change the input format. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [September 1, 2026, 9:03am UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/9 "2026-09-01T09:03:11Z")
For historic reasons, many _hooks_ live in the `user` module and are dynamic. Just wiping these seems a bad idea (as you noted). As you will also wipe term/goal expansion, you are likely to kill far too much. You might get closer to what you want by not wiping predicates marked as `multifile` or not wiping predicates that have a source location, i.e., (part of) their clauses result from loading a file rather than assert/1. The real question is of course what you want to achieve. Quite likely there is a more elegant solution 🙂 ---
**Author:** ![Marc](https://avatars.discourse-cdn.com/v4/letter/m/8dc957/32.png) [@Marc](https://swi-prolog.discourse.group/u/Marc)\ **Post date:** [September 2, 2026, 6:21am UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/10 "2026-09-02T06:21:38Z")
A good, robust solution would be to include the signature of the logical theory in the input data. If only I had understood that 20 years ago … Another solution (which I have chosen for the moment) is a small reduction of the functionality of the code. I want to thank everybody for their responses. One last question: what was the reason that more than a dozen system-like predicates have lost the property “built-in” in between version 8 and version 10? (I hopped over v9 after a long break). I feel that “historical reasons” cannot explain this. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [September 2, 2026, 6:12pm UTC](https://swi-prolog.discourse.group/t/a-new-bug-in-my-old-code/9804/11 "2026-09-02T18:12:18Z")
> [@Marc](#): > > One last question: what was the reason that more than a dozen system-like predicates have lost the property “built-in” in between version 8 and version 10? I don’t know … Built-in predicate detection typically serve a role in meta-interpreters (do not meta-interpret this). I have no clue when this was changed and whether or not this was on purpose. Ideally, the `user` module should be empty and all _hooks_ should live in `prolog` or the module using the hook. History blocks doing so. Net result is that the `user` module contains stuff to keep the system going ☹