From ed3c131ca8b58aa976ec9e2401493acdd3c30b85 Mon Sep 17 00:00:00 2001
From: Mike Roberts <mike.roberts.2k10@googlemail.com>
Date: Mon, 18 Nov 2019 09:43:50 +0000
Subject: [PATCH] Allow comments in rule definitions

---
 examples/lark.lark   |  2 +-
 lark/load_grammar.py |  2 +-
 tests/test_parser.py | 10 ++++++++++
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/examples/lark.lark b/examples/lark.lark
index 915cf2e..7373c54 100644
--- a/examples/lark.lark
+++ b/examples/lark.lark
@@ -44,7 +44,7 @@ _NL: /(\r?\n)+\s*/
 %import common.INT -> NUMBER
 %import common.WS_INLINE
 
-COMMENT: "//" /[^\n]/*
+COMMENT: /\s*/ "//" /[^\n]/*
 
 %ignore WS_INLINE
 %ignore COMMENT
diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index a65ca1e..1070f86 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -85,7 +85,7 @@ TERMINALS = {
     'REGEXP': r'/(?!/)(\\/|\\\\|[^/\n])*?/[%s]*' % _RE_FLAGS,
     '_NL': r'(\r?\n)+\s*',
     'WS': r'[ \t]+',
-    'COMMENT': r'//[^\n]*',
+    'COMMENT': r'\s*//[^\n]*',
     '_TO': '->',
     '_IGNORE': r'%ignore',
     '_DECLARE': r'%declare',
diff --git a/tests/test_parser.py b/tests/test_parser.py
index caee80e..8cefcb8 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -94,6 +94,16 @@ class TestParsers(unittest.TestCase):
         r = g.parse('xx')
         self.assertEqual( r.children[0].data, "c" )
 
+    def test_comment_in_rule_definition(self):
+        g = Lark("""start: a
+               a: "a"
+               // A comment
+               // Another
+                | "b"
+            """)
+        r = g.parse('b')
+        self.assertEqual( r.children[0].data, "a" )
+
     def test_visit_tokens(self):
         class T(Transformer):
             def a(self, children):