Re: How to implement optional semicolon rules

[Matthias Simon]

Thank you for all your answers. The language I am trying to implement 
is quite complex, unfortunately. It has various --and also optional-- 
block-like structures. Hence I personally would prefer setting the 
context variable for the lexer, over rearranging the whole grammar just 
for this nagging semicolon-rule. What I tried was following:

Block
    : '{' Statements '}'
    ;

Statements
    :            Statement Semicolon
    | Statements Statement Semicolon
    ;

Semicolon
    : { driver.expect_semicolon = 1; } ';'
    ;

If expect_semicolon is set and the lexer reads a '}', it then will 
unput this character and return a ';' instead. My problem is, 
expect_semicolon is set _after_ the next is already read and the 
';'-injection is too late. What am I missing?