3 files changed, 75 insertions, 0 deletions
diff --git a/prolog/problems/lists_advanced/len_2/common.py b/prolog/problems/lists_advanced/len_2/common.py
new file mode 100644
index 0000000..93a1faa
--- /dev/null
+++ b/prolog/problems/lists_advanced/len_2/common.py
@@ -0,0 +1,49 @@
+# coding=utf-8
+
+from operator import itemgetter
+import prolog.engine
+import server.problems
+
+id = 119
+number = 26
+visible = False
+facts = None
+
+solution = '''\
+len([], 0).
+len([_|T], Len) :-
+  len(T, LenT),
+  Len is LenT + 1.
+'''
+
+test_cases = [
+    ('len([8, 3, 5, 1], X)',
+        [{'X': '4'}]),
+    ('len([2, -3, 5, 0, 3], X)',
+        [{'X': '5'}]),
+    ('len([], X)',
+        [{'X': '0'}]),
+]
+
+def test(code, aux_code):
+    n_correct = 0
+    engine_id = None
+    try:
+        engine_id, output = prolog.engine.create(code=code+aux_code, timeout=1.0)
+        if engine_id is not None and 'error' not in map(itemgetter(0), output):
+            # Engine successfully created, and no syntax error in program.
+            for query, answers in test_cases:
+                if prolog.engine.check_answers(engine_id, query=query, answers=answers, timeout=1.0):
+                    n_correct += 1
+    except socket.timeout:
+        pass
+    finally:
+        if engine_id:
+            prolog.engine.destroy(engine_id)
+
+    hints = [{'id': 'test_results', 'args': {'passed': n_correct, 'total': len(test_cases)}}]
+    return n_correct, len(test_cases), hints
+
+def hint(code, aux_code):
+    # TODO
+    return []
diff --git a/prolog/problems/lists_advanced/len_2/en.py b/prolog/problems/lists_advanced/len_2/en.py
new file mode 100644
index 0000000..3ca963e
--- /dev/null
+++ b/prolog/problems/lists_advanced/len_2/en.py
@@ -0,0 +1,13 @@
+# coding=utf-8
+
+name = 'len/2'
+slug = 'find the length of a list'
+
+description = '''\
+<p><code>len(L, Len)</code>: <code>Len</code> is the length of the list <code>L</code>.</p>
+<pre>
+?- len([1,2,3], Len).
+  Len = 3.
+</pre>'''
+
+hint = {}
diff --git a/prolog/problems/lists_advanced/len_2/sl.py b/prolog/problems/lists_advanced/len_2/sl.py
new file mode 100644
index 0000000..0e98272
--- /dev/null
+++ b/prolog/problems/lists_advanced/len_2/sl.py
@@ -0,0 +1,13 @@
+# coding=utf-8
+
+name = 'len/2'
+slug = 'Izračunaj dolžino danega seznama'
+
+description = '''\
+<p><code>len(L, Len)</code>: <code>Len</code> je dolžina seznama <code>L</code>.</p>
+<pre>
+?- len([1,2,3], Len).
+  Len = 3.
+</pre>'''
+
+hint = {}