tifier‘0' if there is not enough space on the environment stack. This function succeeds, even if the referenced predicate is not defined. In this case, running the query using PL_next_solution() will return an existence_error. See PL_exception().

The example below opens a query to the predicate is_a/2 to find the ancestor of‘me'. The reference to the predicate is valid for the duration of the process and may be cached by the client.

char *
ancestor(const char *me)
{ term_t a0 = PL_new_term_refs(2);
  static predicate_t p;

  if ( !p )
    p = PL_predicate("is_a", 2, "database");

  PL_put_atom_chars(a0, me);
  PL_open_query(NULL, PL_Q_NORMAL, p, a0);
  ...
}

int PL_next_solution(qid_t qid)

Generate the first (next) solution for the given query. The return value is TRUE if a solution was found, or FALSE to indicate the query could not be proven. This function may be called repeatedly until it fails to generate all solutions to the query.

int PL_cut_query(qid_t qid)

Discards the query, but does not delete any of the data created by the query. It just invalidates qid, allowing for a new call to PL_open_query() in this context. PL_cut_query() may invoke cleanup handlers (see setup_call_cleanup/3) and therefore may experience exceptions. If an exception occurs the return value is FALSE and the exception is accessible through PL_exception(0).

int PL_close_query(qid_t qid)

As