Swi Prolog, unloading source files

Question

Is there a built-in predicate or a easy way to remove from the knowledge database of prolog a source files that has already been consulted? I've gone through the reference manual and didn't find any thing that could do that.

Answer 1

You can do it with these procedures which use source_file/1 and source_file/2:

unload_last_source:-
  findall(Source, source_file(Source), LSource),
  reverse(LSource, [Source|_]),
  unload_source(Source).

unload_source(Source):-
  ground(Source),
  source_file(Pred, Source),
  functor(Pred, Functor, Arity),
  abolish(Functor/Arity),
  fail.
unload_source(_).

unload_source/1 abolishes all predicates defined by the input Source file name. Be warned that it needs to be an absolute path.

unload_last_source/0 will retrieve the last consulted file name and unload it.

Answer 2

After a file has been consulted, it become 'irrelevant' to Prolog. So I think that generally to answer should be no. But SWI-Prolog has a rich set of builtins that allows you to control your prolgram. For instance

?- [stackoverflow].

?- predicate_property(P, file('/home/carlo/prolog/stackoverflow.pl')).
P = yield(_G297, _G298) ;
P = now _G297 ;
P = x(_G297) ;
...

?- abolish(yield/2).
true.

?- predicate_property(P, file('/home/carlo/prolog/stackoverflow.pl')).
P = now _G297 ;
P = x(_G297) ;
...

Note that abolish doesn't require the file name to work, you could delete predicates loaded from other sources files.

clause, clause_property and erase should give more control, but I get an error I don't understand (it's undocumented) when attempting to use erase:

?- clause(strip_spaces(_G297, _G298),X,Y),erase(Y).
ERROR: erase/1: No permission to clause erase `<clause>(0x29acc30)'