Range quantifier syntax in ANTLR Regex

Question

This should be fairly simple. I'm working on a lexer grammar using ANTLR, and want to limit the maximum length of variable identifiers to 30 characters. I attempted to accomplish this with this line(following normal regex - except for the '' thing - syntax):

ID  :   ('a'..'z'|'A'..'Z') ('a'..'z'|'A'..'Z'|'0'..'9'|'_'){0,29}  {System.out.println("IDENTIFIER FOUND.");}
    ;

No errors in code generation, but compilation failed due to a line in the generated code that was simply:

0,29

Obviously antlr is taking the section of text between the brackets and placing it in the accept state area along with the print line. I searched the ANTLR site, and I found no example or reference to an equivalent expression. What should the syntax of this expression be?

Answer 1

ANTLR does not support the {m,n} quantifier syntax. ANTLR sees the {} of your quantifier and can't tell them apart from the {} that surround your actions.

Workarounds:

1. Enforce the limit semantically. Let it gather an unlimited size ID and then complain/truncate it as part of your action code or later in the compiler.
2. Create the quantification rules manually.

This is an example of a manual rule that limits IDs to 8.

SUBID : ('a'..'z'|'A'..'Z'|'0'..'9'|'_')
      ;
ID : ('a'..'z'|'A'..'Z')
     (SUBID (SUBID (SUBID (SUBID (SUBID (SUBID SUBID?)?)?)?)?)?)?
   ;

Personally, I'd go with the semantic solution (#1). There is very little reason these days to limit the identifiers in a language, and even less reason to cause a syntax error (early abort of the compile) when such a rule is violated.