Use abolish/1 instead of erase/1 to remove clauses

Using erase/1 keeps the dynamic property for all defined predicates in
the testing module. This overrides the clauses in solution modules. For
example, if the user defines conc/3 in the solution for the dup/2
problem, the correct conc/3 would not get used even after unloading all
user's clauses.

This commit also plugs a couple of memory leaks by opening (and later
discarding) a new Prolog frame in functions test, load_solution and
mark_solved.

1 files changed, 37 insertions, 9 deletions

diff --git a/prolog/engine.py b/prolog/engine.py
index 7c90d1a..d15704a 100644
--- a/prolog/engine.py
+++ b/prolog/engine.py
@@ -80,12 +80,13 @@ class PrologEngine(object):
 
         # Construct some predicates.
         self.p = {
+            'abolish/1': PL_predicate(b'abolish', 1, None),
             'add_import_module/3': PL_predicate(b'add_import_module', 3, None),
+            'arg/3': PL_predicate(b'arg', 3, None),
             'assertz/1': PL_predicate(b'assertz', 1, None),
-            'assertz/2': PL_predicate(b'assertz', 2, None),
-            'erase/1': PL_predicate(b'erase', 1, None),
             'call_with_time_limit/2': PL_predicate(b'call_with_time_limit', 2, None),
             'consult/1': PL_predicate(b'consult', 1, None),
+            'functor/3': PL_predicate(b'functor', 3, None),
             'message_to_string/2': PL_predicate(b'message_to_string', 2, None),
             'read_term_from_atom/3': PL_predicate(b'read_term_from_atom', 3, None),
             'safe_goal/1': PL_predicate(b'safe_goal', 1, None),
@@ -131,7 +132,8 @@ class PrologEngine(object):
 
         return error_str
 
-    # Call the Prolog predicate [name]. Raise an exception on error.
+    # Call the Prolog predicate [name]. Raise an exception on error. Since this
+    # creates a Termv object, it should be called within an open foreign frame.
     def call(self, name, args):
         qid = PL_open_query(None, self.err_flags, self.p[name], Termv(args).ref)
         try:
@@ -199,15 +201,40 @@ class PrologEngine(object):
     # Loads the correct solution [code] to problem [pid].
     # TODO handle library loading.
     def load_solution(self, pid, code):
+        fid = PL_open_foreign_frame()
         module = 'solution{}'.format(pid)
         for rule in prolog.util.split(code):
             self.call('assertz/1', [Term('{}:({})'.format(module, rule))])
+        PL_discard_foreign_frame(fid)
 
     # Import the correct solution for problem [pid] into module for user [uid].
     def mark_solved(self, uid, pid):
+        fid = PL_open_foreign_frame()
         m_user = 'user{}'.format(uid)
         m_solution = 'solution{}'.format(pid)
         return self.call('add_import_module/3', [Term(m_user), Term(m_solution), Term('end')])
+        PL_discard_foreign_frame(fid)
+
+    # Return the main functor defined by [clause], e.g. dup/2.
+    def predicate_indicator(self, clause):
+        # Return the main functor for [term].
+        def main_functor(term):
+            name = Term()
+            arity = Term()
+            self.call('functor/3', [term, name, arity])
+            return '{}/{}'.format(name, arity)
+
+        fid = PL_open_foreign_frame()
+        clause = Term(clause)
+        functor = main_functor(clause)
+        # Check whether [clause] is a rule or a fact.
+        if functor == ':-/2':
+            # [clause] is a rule, return the main functor for the head.
+            head = Term()
+            self.call('arg/3', [Term(1), clause, head])
+            functor = main_functor(head)
+        PL_discard_foreign_frame(fid)
+        return functor
 
     # Test whether [code] gives the same answer to [query] as the correct
     # solution. The solution for problem [pid] should be loaded beforehand.
@@ -216,6 +243,7 @@ class PrologEngine(object):
         m_user = 'user{}'.format(uid)
         m_solution = 'solution{}'.format(pid)
 
+        fid = PL_open_foreign_frame()
         # Find the correct answers if not already known.
         for query in queries:
             if (pid, query) not in self.answers:
@@ -225,13 +253,12 @@ class PrologEngine(object):
                 self.answers[(pid, query)] = result[0]['X']  # TODO maybe we could check all vars?
 
         correct = True
-        refs = []
+        predicates = set()
         try:
             # Load the user program [code].
             for rule in prolog.util.split(code):
-                ref = Term()
-                if self.call('assertz/2', [Term('{}:({})'.format(m_user, rule)), ref]):
-                    refs.append(ref)
+                self.call('assertz/1', [Term('{}:({})'.format(m_user, rule))])
+                predicates.add(self.predicate_indicator(rule))
 
             for i, query in enumerate(queries):
                 result = self.query(query, m_user)
@@ -240,8 +267,9 @@ class PrologEngine(object):
             correct = False
 
         # Unload all loaded rules.
-        for ref in refs:
-            self.call('erase/1', [ref])
+        for predicate in predicates:
+            self.call('abolish/1', [Term(m_user + ':' + predicate)])
+        PL_discard_foreign_frame(fid)
 
         return correct