fix

1 files changed, 2 insertions, 1 deletions

diff --git a/grammar.rb b/grammar.rb
index ea16425..0b2bc61 100644
--- a/grammar.rb
+++ b/grammar.rb
@@ -33,7 +33,8 @@ class NT
   end
 
   def to_s
-    "NT<#{@symbol},#{@index}>"
+    return "NT<#{@symbol},#{@index}>" if @index>=0
+    return "NT<#{@symbol}>"
   end
 end