Mark solution predicates as static after loading

This prevents incorrect student solutions from overwriting or adding to
predicates in solution<n> modules.

1 files changed, 11 insertions, 4 deletions

diff --git a/prolog/engine.py b/prolog/engine.py
index 07489df..088948e 100644
--- a/prolog/engine.py
+++ b/prolog/engine.py
@@ -85,6 +85,7 @@ class PrologEngine(object):
             'arg/3': PL_predicate(b'arg', 3, None),
             'assertz/1': PL_predicate(b'assertz', 1, None),
             'call_with_time_limit/2': PL_predicate(b'call_with_time_limit', 2, None),
+            'compile_predicates/1': PL_predicate(b'compile_predicates', 1, 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),
@@ -116,19 +117,25 @@ 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)
+
+        fid = PL_open_foreign_frame()
+        predicates = set()
         for rule in prolog.util.split(code):
             self.call('assertz/1', [Term('{}:({})'.format(module, rule))])
+            predicates.add('{}:{}'.format(module, self.predicate_indicator(rule)))
+        self.call('compile_predicates/1', [Term([Term(p) for p in predicates])])
         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')])
+
+        fid = PL_open_foreign_frame()
+        result = self.call('add_import_module/3', [Term(m_user), Term(m_solution), Term('end')])
         PL_discard_foreign_frame(fid)
+        return result
 
     # 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
@@ -206,7 +213,7 @@ class PrologEngine(object):
                 self.call('assertz/1', [Term('{}:({})'.format(m_user, rule))])
                 predicates.add(self.predicate_indicator(rule))
 
-            for i, query in enumerate(queries):
+            for query in queries:
                 result = self.query(query, m_user)
                 correct &= (len(result) == 1 and result[0]['X'] == self.answers[(pid, query)])
         except Exception as ex: