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Re: Programmatically consulting a prolog file

From: Daniel Diaz
Subject: Re: Programmatically consulting a prolog file
Date: Mon, 12 Apr 2010 16:47:45 +0200
User-agent: Thunderbird (X11/20100317)


looking at your portion of code I think the problem comes from your first query calling absolute_file_name/2. When you close this query you use PL_RECOVER which means that all Prolog stacks are restored, in particular the Prolog heap. So you should not trust any Prolog term computed by the query because maybe it is in the heap (this portion of the heap will be reused in the next query). Here are possible solutions:
  • don't call absolute_file_name/2 (consult/1 does it for you !). See extract below:
  • in your first query replace Pl_Query_End(PL_RECOVER) by Pl_Query_End(PL_CUT)
  • in your first query replace Pl_Query_Begin(PL_TRUE) by Pl_Query_Begin(PL_FALSE)
  • in your first query replace  arg[0] = arg[1];   by   arg[0] = Pl_Mk_Atom(Pl_Rd_Atom(arg[1]));
All these solutions should work.

About Pl_Write_Simple(): you can use it to display a Prolog term like this:

  arg[0] = Pl_Mk_String("");

  printf("consulting "); Pl_Write_Simple(arg[0]); printf("...\n");

  func = Pl_Find_Atom("consult");

  res = Pl_Query_Call(func, 1, arg);
  if (res == PL_EXCEPTION) {
    printf("exception "); Pl_Write_Simple(
Pl_Get_Exception()); printf("\n");


josh b a écrit :

pl2wam was not in my path, so I added it. Didn't make any difference.

I could not find any function called Pl_Write_Simple(), however, I did try various things like Pl_Rd_String() and Pl_Exec_Continuation(Pl_Find_Atom("throw"), 1, &except);    (Where except was the variable returned from Pl_Get_Exception()).

However, doing anything with except produces an access violation error. In fact, doing anything with any term after trying to consult causes access violations, even with terms that were available and working before hand and were unmodified. Additionally, using Pl_Exec_Continuation anywhere in the code seems to cause a violation.

Initially to get it to work, I had to recompile Prolog, using the instructions (Followed exactly, save for directory locations) found at Just wondering if that could be causing all these violations.


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