[antlr-interest] Can't figure out the ambiguity leading to this unreachable token def

[Kamil Burzynski]

Hello Dan,

Dan wrote:
> Thanks Kamil.
> But when you look at my grammar, doesn't the "expr" rule make it clear
> that only the "VALUE" rule can match what's inside the single quotes?

Lexer do not look at expr rule. expr is parser rule. In general it works 
like this:

- in case of parser/lexer combined grammar (like your) rule with name 
beginning with small letter is parser rule, while capital letter at 
beginning of rule name indicates lexer rule.

- so, you have expr parser rule and NAME/VALUE lexer rules

- the first thing your generated code does is just to split input 
characters into tokens, using lexer rules. Parser rules will be later 
used to process resulting token stream.

- lexer therefore is not aware of context - it just matches characters,
so such definition of NAME and VALUE is ambiguous for it.

I suggest rewriting VALUE to :

VALUE = '\'' ('a'..'z' | 'A'..'Z')+ '\''

and remove ' from expr.

--
Best regards from
Kamil Burzynski