antlr4 grammar fails to match initial identifier

Question

I have a grammar that is failing on the first token. I've stripped it down some to reduce the choices, but still have the error:

line 1:0 mismatched input 'main' expecting {, '@', 'def', IDENTIFIER}

I expect the token 'main' to match IDENTIFIER, which has this lexical production:

IDENTIFIER : [a-zA-Z][a-zA-Z0-9]*;

Why would that be failing?

Sam Harwell Sam Harwell · Accepted Answer · 2014-01-27T23:48:45

One of the following is happening:

You have another rule in the grammar located before IDENTIFIER that also matches the input main.
You have a combined grammar (declared as grammar T instead of parser grammar T or lexer grammar T), where one of the parser rules contains the literal 'main' which is causing a separate lexer rule to be implicitly created for this literal.