From 1a602429e86680d82a5ab8064386e66a1126cf36 Mon Sep 17 00:00:00 2001
From: Timotej Lazar <timotej.lazar@fri.uni-lj.si>
Date: Sun, 20 Mar 2016 10:03:51 +0100
Subject: Prolog: add triggers for sum/len hints

---
 prolog/problems/lists_advanced/len_2/common.py | 40 ++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 3 deletions(-)

(limited to 'prolog/problems/lists_advanced/len_2/common.py')

diff --git a/prolog/problems/lists_advanced/len_2/common.py b/prolog/problems/lists_advanced/len_2/common.py
index 501a4f8..6caea98 100644
--- a/prolog/problems/lists_advanced/len_2/common.py
+++ b/prolog/problems/lists_advanced/len_2/common.py
@@ -24,6 +24,12 @@ hint_type = {
     'base_case': Hint('base_case'),
     'recursive_case': Hint('recursive_case'),
     'timeout': Hint('timeout'),
+    'arbitrary_base_case': Hint('arbitrary_base_case'),
+    'args_not_instantiated': Hint('arbitrary_base_case'),
+    '=_instead_of_is': Hint('=_instead_of_is'),
+    '+H_instead_of_+1': Hint('+H_instead_of_+1'),
+    'forcing_result_onto_recursion': Hint('forcing_result_onto_recursion'),
+    'same_var_on_both_sides_of_is': Hint('same_var_on_both_sides_of_is'),
 }
 
 test_cases = [
@@ -68,13 +74,41 @@ def hint(code, aux_code):
             return [{'id': 'eq_instead_of_equ_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
                    [{'id': 'eq_instead_of_equ'}]
 
+        # target predicate seems to always be false
+        if not prolog.engine.ask_truthTO(engine_id, 'len(_, _)'):
+            return [{'id': 'predicate_always_false'}]
+
+        # arbitrary base case: len([], _)
+        if prolog.engine.ask_truthTO(engine_id, 'len([], q), len([], child(Q, q))'):
+            return [{'id': 'arbitrary_base_case'}]
+
         # missing/failed base case
         if not prolog.engine.ask_truthTO(engine_id, 'len([], 0)'):
             return [{'id': 'base_case'}]
 
-        # target predicate seems to always be false
-        if not prolog.engine.ask_truthTO(engine_id, 'len(_, _)'):
-            return [{'id': 'predicate_always_false'}]
+        # arguments not instantiated
+        reply, output = prolog.engine.ask(engine_id, 'len([a, b, c], Len)', timeout=1)
+        if reply.get('code') == 'instantiation_error':
+            return [{'id': 'args_not_instantiated'}]
+
+        # = instead of is
+        if prolog.engine.ask_truthTO(engine_id, 'len([qa, qb, qc, qd], _+_)'):
+            return [{'id': '=_instead_of_is'}]
+
+        # +H instead of +1
+        if prolog.engine.ask_truthTO(engine_id, 'len([1, 3, 9, 27, 81], 121)'):
+            return [{'id': '+H_instead_of_+1'}]
+
+        # forcing result onto recursion
+        if prolog.engine.ask_truthTO(engine_id, '''\
+                asserta(len([9, 81], 2+1)), len([27, 9, 81], 2), retract(len([9, 81], 2+1))
+                ;
+                asserta(len([9, 81], 1+2)), len([27, 9, 81], 2), retract(len([9, 81], 1+2))'''):
+            return [{'id': 'forcing_result_onto_recursion'}]
+
+        # same var on both sides of is
+        if prolog.engine.ask_truth(engine_id, 'len([], 0), \+ len([a, b, c], _)'):
+            return [{'id': 'same_var_on_both_sides_of_is'}]
 
         # base case works, the recursive doesn't (but it doesn't timeout)
         # this may be left as the last, most generic hint
-- 
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