Re: Trying to add facts during runtime in VC++

[Vic Bancroft]

On Mon, 17 Feb 2003 address@hidden wrote:

> Lindsey Spratt said:
> >
> > On Monday, February 17, 2003, at 04:30  PM, Joseph N. Fiore wrote:
> >
> >> Now.  While the C program is running, it learns from an outside
> >> source, that John has a son named Joe.  How do I tell GNU-Prolog from
> >> the C program, the new fact?  parent(john,joe).
> >
> > Make sure that you have declared parent/2 dynamic.

This can be done in gprolog with a directive in you prolog,

  :- dynamic( parent/2 ).

> > Then I think you want to evaluate a gprolog query using the builtin
> > assert/1:
> >
> > assert(parent(john, joe)).

Well actually, you need assertz/1.  For porting convenience assert/1 can be
easily added.  

> Maybe I wasn't clear.  How do an assert from a C program at runtime?
> The only C source code examples I've seen are for queries with a Pl_Query.

Perhaps after reading gprolog/examples/ExamplesC/new_main_c. Lindsey's
answer will make more sense.  If you make modifications, such as,

  int func, assert, parent;

  WamWord arg[10], trm[10];

  char str[100];
  char *sol[100];
  int i, nb_sol = 0;
  Bool res;

  Start_Prolog(argc, argv);

  func = Find_Atom("anc");

  assert = Find_Atom("assertz");
  parent = Find_Atom("parent");
  arg[0] = Mk_String("john");
  arg[1] = Mk_String("joe");
  trm[0] = Mk_Compound( parent, 2, arg);
  Pl_Query_Begin(TRUE);
  res = Pl_Query_Call(assert, 1, trm);
  Pl_Query_End(PL_RECOVER);
    
You will notice that now joe has ancestors,

  $ ./new_main 

  Enter a name (or 'end' to finish): joe
    solution: john
    solution: bob
    solution: jane
    solution: mary
    solution: paul
    solution: peter
  6 solution(s)

more,
l8r,

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