From aef533920831d96a4d39271bdbcbcd8e2e76bc4c Mon Sep 17 00:00:00 2001
From: Timotej Lazar <timotej.lazar@fri.uni-lj.si>
Date: Sun, 13 Mar 2016 21:20:00 +0100
Subject: Prolog: add generic style check for ":- false."

---
 prolog/common.py | 17 +++++++++++++----
 prolog/sl.py     |  4 ++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/prolog/common.py b/prolog/common.py
index 5f16364..16f7769 100644
--- a/prolog/common.py
+++ b/prolog/common.py
@@ -2,6 +2,7 @@
 
 import operator
 import prolog.engine
+from prolog.util import tokenize
 from server.hints import Hint, HintPopup
 
 id = 1
@@ -36,7 +37,15 @@ def check_syntax(code, aux_code):
     return []
 
 def hint(code, aux_code):
-    tokens = prolog.util.tokenize(code)
+    tokens = tokenize(code)
+    hints = []
+
+    # rules like a(X) :- fail.
+    for i, t in enumerate(tokens[:-2]):
+        t1 = tokens[i+1]
+        t2 = tokens[i+2]
+        if t.val == ':-' and t1.val in ('fail', 'false') and t2.val == '.':
+            hints += [{'id': 'fail_rule_markup', 'start': t.pos, 'end': t2.pos + len(t2.val)}]
 
     # a,b,c are a bit dangerous when crossing the river exercise is being solved
     # what about potential numbers after letters?
@@ -44,7 +53,7 @@ def hint(code, aux_code):
     targets = {'a', 'b', 'c', 'x', 'y', 'z', 'h', 't', 'l', 's', 'v', 'w'}
     marks = [(t.pos, t.pos + len(t.val)) for t in tokens if t.type == 'NAME' and t.val in targets]
     if marks:
-        return [{'id': 'noncapitalised_variable_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
-               [{'id': 'noncapitalised_variable'}]
+        hints += [{'id': 'noncapitalised_variable_markup', 'start': m[0], 'end': m[1]} for m in marks] + \
+                 [{'id': 'noncapitalised_variable'}]
 
-    return []
+    return hints
diff --git a/prolog/sl.py b/prolog/sl.py
index 095d253..ea15f93 100644
--- a/prolog/sl.py
+++ b/prolog/sl.py
@@ -52,5 +52,9 @@ hint = {
 
     'noncapitalised_variable_markup': '''\
 <p>Je prav, da je to pisano z malo?</p>
+''',
+
+    'fail_rule_markup': '''\
+<p>Pravila, ki nikoli ne drži, nikoli ne potrebuješ.</p>
 ''',
 }
-- 
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