Prolog: add generic recursion hints for lists_advanced problems

TODO modify texts in */sl.py where appropriate.

1 files changed, 46 insertions, 4 deletions

diff --git a/prolog/problems/lists_advanced/evenlen_1_+_oddlen_1/common.py b/prolog/problems/lists_advanced/evenlen_1_+_oddlen_1/common.py
index 1236551..256b090 100644
--- a/prolog/problems/lists_advanced/evenlen_1_+_oddlen_1/common.py
+++ b/prolog/problems/lists_advanced/evenlen_1_+_oddlen_1/common.py
@@ -1,8 +1,9 @@
-# coding=utf-8
-
 from operator import itemgetter
+import socket
+
 import prolog.engine
-import server.problems
+import prolog.util
+from server.hints import Hint, HintPopup
 
 id = 116
 number = 23
@@ -19,6 +20,15 @@ oddlen([_,_|T]) :-
   oddlen(T).
 '''
 
+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'),
+}
+
 test_cases = [
     ('evenlen([])',
         [{}]),
@@ -52,5 +62,37 @@ 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'}]
+
+        # missing/failed base case
+        if not prolog.engine.ask_truthTO(engine_id, 'evenlen([]), oddlen([a])'):
+            return [{'id': 'base_case'}]
+
+        # target predicate seems to always be false
+        if not prolog.engine.ask_truthTO(engine_id, 'evenlen(_) ; oddlen(_)'):
+            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, 'evenlen([2, 41, -22, 13])'):
+            return [{'id': 'recursive_case'}]
+
+    except socket.timeout as ex:
+        return [{'id': 'timeout'}]
+
+    finally:
+        if engine_id:
+            prolog.engine.destroy(engine_id)
+
     return []