From a4e8456ab5f14a34cb2f79c0946c439a976041f8 Mon Sep 17 00:00:00 2001
From: Aleksander Sadikov <aleksander.sadikov@fri.uni-lj.si>
Date: Mon, 14 Mar 2016 03:44:53 +0100
Subject: Hints for last_elem/2 added.

---
 prolog/problems/lists/last_elem_2/common.py | 17 +++++++++++++++--
 prolog/problems/lists/last_elem_2/sl.py     | 13 +++++++++++++
 2 files changed, 28 insertions(+), 2 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 8c08d61..75cec75 100644
--- a/prolog/problems/lists/last_elem_2/common.py
+++ b/prolog/problems/lists/last_elem_2/common.py
@@ -26,6 +26,9 @@ hint_type = {
     'recursive_case': Hint('recursive_case'),
     'timeout': Hint('timeout'),
     'final_hint': Hint('final_hint'),
+    '[]_should_not_succeed': Hint('[]_should_not_succeed'),
+    'list_returned': Hint('list_returned'),
+    'clumsy_conc_use': Hint('clumsy_conc_use'),
 }
 
 test_cases = [
@@ -74,6 +77,18 @@ 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'}]
+
+        # 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'}]
 
         # missing/failed base case
         if not prolog.engine.ask_truthTO(engine_id, 'last_elem([qQ], qQ)'):
@@ -89,8 +104,6 @@ def hint(code, aux_code):
         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'}]
 
diff --git a/prolog/problems/lists/last_elem_2/sl.py b/prolog/problems/lists/last_elem_2/sl.py
index c0d8082..bcc33f8 100644
--- a/prolog/problems/lists/last_elem_2/sl.py
+++ b/prolog/problems/lists/last_elem_2/sl.py
@@ -36,6 +36,19 @@ implicitno že kar v argumentih predikata (glavi stavka).</p>
 
     'base_case': '''\
 <p>Si pomislil na robni pogoj? Kaj je najbolj enostaven primer? Kaj, če ima seznam samo en element?</p>
+''',
+
+    '[]_should_not_succeed': '''\
+<p>Kako si lahko uspešno našel zadnji element v praznem seznamu? Verjetno potrebuješ drugačen robni pogoj.</p>
+''',
+
+    'list_returned': '''\
+<p>Vračaš seznam namesto elementa.</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>
 ''',
 
     'recursive_case': '''\
-- 
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