From 71772851de61a77598bd5ffc2e729a82d5da6416 Mon Sep 17 00:00:00 2001
From: Aleksander Sadikov <aleksander.sadikov@fri.uni-lj.si>
Date: Mon, 14 Mar 2016 04:06:03 +0100
Subject: Hints for last_elem/2 updated.

---
 prolog/problems/lists/last_elem_2/common.py | 14 ++++++++++----
 prolog/problems/lists/last_elem_2/sl.py     |  5 +++++
 2 files changed, 15 insertions(+), 4 deletions(-)

(limited to 'prolog/problems/lists')

diff --git a/prolog/problems/lists/last_elem_2/common.py b/prolog/problems/lists/last_elem_2/common.py
index 75cec75..9c44231 100644
--- a/prolog/problems/lists/last_elem_2/common.py
+++ b/prolog/problems/lists/last_elem_2/common.py
@@ -29,6 +29,7 @@ hint_type = {
     '[]_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 = [
@@ -77,15 +78,20 @@ def hint(code, aux_code):
 
         # recursion is getting bigger and bigger
 
-        # 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'}]
-
         # 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_truthTO(engine_id, 'last_elem([q], X), is_list(X)'):
             return [{'id': 'list_returned'}]
diff --git a/prolog/problems/lists/last_elem_2/sl.py b/prolog/problems/lists/last_elem_2/sl.py
index bcc33f8..7ab8ddc 100644
--- a/prolog/problems/lists/last_elem_2/sl.py
+++ b/prolog/problems/lists/last_elem_2/sl.py
@@ -49,6 +49,11 @@ implicitno že kar v argumentih predikata (glavi stavka).</p>
     'clumsy_conc_use': '''\
 <p>Uporabljaš <code>conc/3</code>? Zanimiva ideja. Ne pozabi, da mora drugi seznam, ki ga konkateniraš
 biti dolžine ena, če hočeš doseči to kar želiš. Torej vzorec oblike <code>[X]</code>, kajne?</p>
+''',
+
+    'unsuccessful_conc_use': '''\
+<p>Uporabljaš <code>conc/3</code>? Zanimiva ideja, da se rešiti tudi tako. Vendar boš moral še malo premisliti.
+Ne pozabi, <code>conc/3</code> ima tri argumente, vsi so seznami. Premisli, kakšen vzorec potrebuješ...</p>
 ''',
 
     'recursive_case': '''\
-- 
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