1 files changed, 70 insertions, 1 deletions
diff --git a/prolog/problems/lists/divide_3/common.py b/prolog/problems/lists/divide_3/common.py
index 969cdec..2d20f12 100644
--- a/prolog/problems/lists/divide_3/common.py
+++ b/prolog/problems/lists/divide_3/common.py
@@ -2,6 +2,9 @@
 
 from operator import itemgetter
 import prolog.engine
+import prolog.util
+import socket
+from server.hints import Hint, HintPopup
 import server.problems
 
 id = 115
@@ -16,6 +19,19 @@ divide([H1,H2|T], [H1|L1], [H2|L2]) :-
   divide(T, L1, L2).
 '''
 
+hint_type = {
+    'eq_instead_of_equ_markup': HintPopup('eq_instead_of_equ_markup'),
+    'eq_instead_of_equ': Hint('eq_instead_of_equ'),
+    'predicate_always_false': Hint('predicate_always_false'),
+    'base_case': Hint('base_case'),
+    'recursive_case': Hint('recursive_case'),
+    'timeout': Hint('timeout'),
+    '[]_should_not_succeed': Hint('[]_should_not_succeed'),
+    'list_returned': Hint('list_returned'),
+    'clumsy_conc_use': Hint('clumsy_conc_use'),
+    'unsuccessful_conc_use': Hint('unsuccessful_conc_use'),
+}
+
 test_cases = [
     ('divide([], A, B)',
         [{'A': '[]', 'B': '[]'}]),
@@ -49,5 +65,58 @@ def test(code, aux_code):
     return n_correct, len(test_cases), hints
 
 def hint(code, aux_code):
-    # TODO
+    tokens = prolog.util.tokenize(code)
+
+    try:
+        engine_id, output = prolog.engine.create(code=code+aux_code, timeout=1.0)
+
+        # strict equality testing instead of simple matching
+        # this is usually (but not necessarily) wrong
+        targets = [prolog.util.Token('EQ', '==')]
+        marks = [(t.pos, t.pos + len(t.val)) for t in tokens if t in targets]
+        if marks:
+            return [{'id': 'eq_instead_of_equ_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
+                   [{'id': 'eq_instead_of_equ'}]
+
+        # recursion is getting bigger and bigger
+
+        # using conc, but clumsily: conc(_, X, L) instead of conc(_, [X], L)
+        if prolog.util.Token('NAME', 'conc') in tokens and \
+           prolog.engine.ask_truthTO(engine_id, 'last_elem([q,a,b,c], [q,a,b,c])'):
+            return [{'id': 'clumsy_conc_use'}]
+
+        # general unsuccessful use of conc, but not specifically detected
+        # return general_conc hint, not to confuse/force the student into a non-conc solution
+        if prolog.util.Token('NAME', 'conc') in tokens:
+            return [{'id': 'unsuccessful_conc_use'}]
+
+        # succeeds when asked to return the last element of an empty list
+        if prolog.engine.ask_truthTO(engine_id, 'last_elem([], _)'):
+            return [{'id': '[]_should_not_succeed'}]
+
+        # returns a list, not an element as required
+        if prolog.engine.ask_one(engine_id, 'last_elem([qQ], [qQ])'):  # 'last_elem([qQ], X), is_list(X)' with ask_one?
+            return [{'id': 'list_returned'}]
+
+        # missing/failed base case
+        if not prolog.engine.ask_one(engine_id, 'last_elem([qQ], qQ)'):
+            return [{'id': 'base_case'}]
+
+        # target predicate seems to always be false
+        if not prolog.engine.ask_truthTO(engine_id, 'last_elem(_, _)') and \
+           not prolog.engine.ask_truthTO(engine_id, 'last_elem([_,_,_,_,_,_], _)'):
+            return [{'id': 'predicate_always_false'}]
+
+        # base case works, the recursive doesn't (but it doesn't timeout)
+        # this may be left as the last, most generic hint
+        if not prolog.engine.ask_truth(engine_id, 'last_elem([qa,qb,qQ,qc], qc)'):
+            return [{'id': 'recursive_case'}]
+
+    except socket.timeout as ex:
+        return [{'id': 'timeout'}]
+
+    finally:
+        if engine_id:
+            prolog.engine.destroy(engine_id)
+
     return []