diff options
| -rw-r--r-- | prolog/engine.py | 103 |
1 files changed, 58 insertions, 45 deletions
diff --git a/prolog/engine.py b/prolog/engine.py index 26215f8..7c90d1a 100644 --- a/prolog/engine.py +++ b/prolog/engine.py @@ -112,74 +112,87 @@ class PrologEngine(object): # Dictionary of correct answers; keys are (pid, query). self.answers = {} - def exception(self, qid): - ref = PL_exception(qid) - if not ref: - return False - try: - ex = Term(ref=ref) - msg = Term() - if PL_call_predicate(None, self.err_flags, - self.p['message_to_string/2'], Termv([ex, msg]).ref): - raise Exception(str(msg)) - raise Exception('Unknown error') - finally: - PL_clear_exception() - return False + # Return a description of the last exception, or None if no error occurred. + def error(self, qid): + error_ref = PL_exception(qid) + if not error_ref: + return None + PL_clear_exception() + + # Get the Prolog error message. + fid = PL_open_foreign_frame() + msg = Term() + if PL_call_predicate(None, self.err_flags, self.p['message_to_string/2'], + Termv([Term(ref=error_ref), msg]).ref): + error_str = str(msg) + else: + error_str = 'Unknown error' + PL_discard_foreign_frame(fid) + + return error_str + # Call the Prolog predicate [name]. Raise an exception on error. def call(self, name, args): qid = PL_open_query(None, self.err_flags, self.p[name], Termv(args).ref) try: if not PL_next_solution(qid): - if not self.exception(qid): - return False + error_msg = self.error(qid) + if error_msg: + raise Exception(error_msg) + return False finally: PL_cut_query(qid) return True - # Get up to [n] solutions to query [q]. + # Get up to [n] solutions to query [q]. If there are no solutions, return + # an empty list. Raise an exception on error (either from self.call, or due + # to malformed/unsafe query or a timeout). def query(self, q, module=None, n=1): if module is not None: q = '{}:({})'.format(module, q) fid = PL_open_foreign_frame() - - var_names = Term() - options = Term([Term('variable_names', [var_names])]) - goal = Term() + qid = None try: - # Parse term and store variable names. + # Parse the query and store variable names. + goal = Term() + var_names = Term() + options = Term([Term('variable_names', [var_names])]) if not self.call('read_term_from_atom/3', [Term(Atom(q)), goal, options]): raise Exception('Warning: Could not read term from {}\n'.format(q)) + # Check if goal is safe with currently loaded rules. if not self.call('safe_goal/1', [goal]): raise Exception('Warning: Unsafe goal: {}\n'.format(goal)) - except Exception as ex: - raise - solutions = Term() - goal_aux = Term('findnsols', [Term(n), goal, goal, solutions]) - qid = PL_open_query(None, self.err_flags, self.p['call_with_time_limit/2'], - Termv([Term(0.01), goal_aux]).ref) + solutions = Term() + goal_aux = Term('findnsols', [Term(n), goal, goal, solutions]) + qid = PL_open_query(None, self.err_flags, self.p['call_with_time_limit/2'], + Termv([Term(0.01), goal_aux]).ref) - result = [] - if PL_next_solution(qid): - for solution in solutions: + result = [] + if PL_next_solution(qid): fid_solution = PL_open_foreign_frame() - PL_unify(goal.ref, solution.ref) - variables = {} - for var in var_names: - name, value = Term(), Term() - PL_get_arg(1, var.ref, name.ref) - PL_get_arg(2, var.ref, value.ref) - variables[str(name)] = str(value) - result.append(variables) - PL_rewind_foreign_frame(fid_solution) - else: - self.exception(qid) - - PL_close_query(qid) - PL_discard_foreign_frame(fid) + for solution in solutions: + PL_unify(goal.ref, solution.ref) + variables = {} + for var in var_names: + name, value = Term(), Term() + PL_get_arg(1, var.ref, name.ref) + PL_get_arg(2, var.ref, value.ref) + variables[str(name)] = str(value) + result.append(variables) + PL_rewind_foreign_frame(fid_solution) + PL_discard_foreign_frame(fid_solution) + else: + # Check for exceptions. + error_msg = self.error(qid) + if error_msg: + raise Exception(error_msg) + finally: + if qid: + PL_close_query(qid) + PL_discard_foreign_frame(fid) return result |