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prologpersistence

Persistence of facts in Prolog

I'm kinda new in Prolog and I'm using SWI-Prolog v6.6 to storage asserts in a *.pl file.

:- dynamic fact/2.

assert(fact(fact1,fact2)).

With the code above I can make asserts and it works fine, but the problem is when I close SWI-Prolog and I open the *.pl file again, the asserts I've made are gone...

Is there a way to make asserts and those get stored even if I exit the Prolog process?

Sorry about my bad english and Thanks! (:

Solution

  • Saving state has certain limitations, also see the recent discussion on the SWI-Prolog mailing list.

    I think the easiest way to persistently store facts on SWI-Prolog is to use the persistency library. For that I would rewrite your code in the following way:

    :- use_module(library(persistency)).

:- persistent fact(fact1:any, fact2:any).

:- initialization(init).

init:-
  absolute_file_name('fact.db', File, [access(write)]),
  db_attach(File, []).

    You can now add/remove facts using assert_fact/2, retract_fact/2, and retractall_fact/2.

    Upon exiting Prolog the asserted facts are automatically saved to fact.db.

    Example usage:

    $ swipl my_facts.pl
?- assert_fact(some(fact), some(other,fact)).
true.
?- halt.
$ swipl my_facts.pl
?- fact(X, Y).
X = some(fact),
Y = some(other, fact).