[antlr-interest] Any clue for this internal error?

[Meng Tian]

Hello

I am new to ANTLR, and I try to start with a very simple grammar definition
(as follows).

=======================================
grammar CL;

    fragment INPUTS : 'A' | 'B' | 'C' | 'D' | 'E' | 'F';
    fragment OUTPUTS : 'U' | 'V' | 'X' | 'Y' | 'Z';

    fragment INPUT : 'i';
    fragment OUTPUT : 'o';

    ACTION : ( INPUT INPUTS ) | ( OUTPUT OUTPUTS );
=======================================

I was expecting that strings like "iA" and "oU" should be successfully
recognized and given the "ACTION" token. But when I run "java
org.antlr.Tool CL.g", I had the following error message:

=======================================
error(10):  internal error: CL.g : java.lang.ClassCastException:
org.antlr.runtime.tree.CommonTree cannot be cast to
org.antlr.tool.GrammarAST
org.antlr.grammar.v3.CodeGenTreeWalker.rules(CodeGenTreeWalker.java:1467)
org.antlr.grammar.v3.CodeGenTreeWalker.grammarSpec(CodeGenTreeWalker.java:1441)
org.antlr.grammar.v3.CodeGenTreeWalker.grammar_(CodeGenTreeWalker.java:509)
org.antlr.codegen.CodeGenerator.genRecognizer(CodeGenerator.java:421)
org.antlr.Tool.generateRecognizer(Tool.java:655)
org.antlr.Tool.process(Tool.java:468)
org.antlr.Tool.main(Tool.java:93)
=======================================

I have no idea about this error. Any clue on this?

Thank you.


Regards,
Meng