1 files changed, 55 insertions, 1 deletions
diff --git a/prolog/problems/lists/last_elem_2/common.py b/prolog/problems/lists/last_elem_2/common.py
index b18243d..4014b13 100644
--- a/prolog/problems/lists/last_elem_2/common.py
+++ b/prolog/problems/lists/last_elem_2/common.py
@@ -1,3 +1,5 @@
+# coding=utf-8
+
 from operator import itemgetter
 import prolog.engine
 import prolog.util
@@ -6,14 +8,24 @@ from server.hints import Hint, HintPopup
 import server.problems
 
 id = 10000
-number = 2
+number = 6
 visible = True
 facts = None
 
 solution = '''\
+last_elem([X], X).
+last_elem([_|T], X) :-
+  last_elem(T, X).
 '''
 
 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'),
+    'final_hint': Hint('final_hint'),
 }
 
 test_cases = [
@@ -40,7 +52,49 @@ def test(code, aux_code):
             prolog.engine.destroy(engine_id)
 
     hints = [{'id': 'test_results', 'args': {'passed': n_correct, 'total': len(test_cases)}}]
+    if n_correct == len(test_cases):
+        tokens = prolog.util.tokenize(code)
+        if prolog.util.Token('NAME', 'conc') not in tokens or prolog.util.Token('NAME', 'append') not in tokens:
+            hints += [{'id': 'final_hint'}]
     return n_correct, len(test_cases), hints
 
 def hint(code, aux_code):
+    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
+
+
+        # missing/failed base case
+        if not prolog.engine.ask_truthTO(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([_,_,_,_,_,_], _)'):
+            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'}]
+
+        # TODO: Tim, can we include 'fail'-used as a general hint?
+
+    except socket.timeout as ex:
+        return [{'id': 'timeout'}]
+
+    finally:
+        if engine_id:
+            prolog.engine.destroy(engine_id)
+
     return []