[antlr-interest] Lexer strangeness

[Clifford Heath]

New to Antlr, not to parser-generators. Hi all!
I'm using ANTLRWorks downloaded today on a MAC under OS/X.

I have the following snippet which works when I do it this way:

IDENTIFIER: ID;
fragment ID: LETTER ( ( LETTER|DIGIT )* LETTER)? DIGIT?;
// with:
fragment LETTER	:	('_'|'A'..'Z'|'a'..'z');
fragment DIGIT: '0'..'9';

but not when I do it this way:

IDENTIFIER: ID DIGIT?;
fragment ID: LETTER ( ( LETTER|DIGIT )* LETTER)?;

In the latter case it fails to match the IDENTIFIER 'f3', for example.

I have it structured this way because in the full grammar,
I have two similar things:
IDENTIFIER: ID;
VARIABLE: ID DIGIT?;

where IDENTIFIER may not end with a digit, but VARIABLE might.
Use of a VARIABLE always makes the lexer/parser fail. I thought
I might have an greedy/non-greedy problem here, but even without
the similar definitions, the above fails.

What's happening here? Can someone point me in the right direction please?

Clifford Heath.