Your example is ambiguous as well as left recursive. I assume you meant one of the following:
a : a B | A; a : A* B | A; The first can be written as: a : A (B^)*; The second can be written as a : A (A* B^)? | A | B; Sam -----Original Message----- From: antlr-interest-boun...@antlr.org [mailto:antlr-interest-boun...@antlr.org] On Behalf Of Luigi Iannone Sent: Thursday, July 21, 2011 8:00 AM To: ANTLR Subject: [antlr-interest] Left recursive grammar Hi all, I have this simple grammar grammar test; options { language = Java; output = AST; } a : a*B ->^(B a*) | A ; B : '.B' ; A : 'A' ; and I get the following output when I try to generate the parser in ANTRLWorks [13:48:53] error(210): The following sets of rules are mutually left-recursive [a] I read on the Web that there are solutions to solve this, however they will mess up the associativity, which I need to keep instead. So, for instance, for the input A.B.B the AST tree should be ^(B ^(B A)) Is there any way to change the grammar in order to eliminate the left recursion and obtain the above tree. I am afraid I do not get how to do it by just looking at what is there online about left recursive grammars. Thanks a lot for your help, Luigi List: http://www.antlr.org/mailman/listinfo/antlr-interest Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your-email-address List: http://www.antlr.org/mailman/listinfo/antlr-interest Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your-email-address -- You received this message because you are subscribed to the Google Groups "il-antlr-interest" group. To post to this group, send email to il-antlr-inter...@googlegroups.com. To unsubscribe from this group, send email to il-antlr-interest+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/il-antlr-interest?hl=en.
