[antlr-interest] Re: Calc example LPAREN/RPAREN

[kemmerzehl]

--- In antlr-interest at y..., "kemmerzehl" <malitrait at s...> wrote:
> Hi,
>   This is my first exposure to parsing etc. so please excuse my 
> ignorance. As an excersize in trying and figure this stuff out i 
set 
> myself the task of modifying the calc example to support input such 
> as "(5+4)*3;" but i cannot figure out what im supposed to do. I 
know 
> you guys probably hate these messages but im having trouble getting 
> my head around this and i havent been able to find "The Complete 
> Idiots Guide to ANTLR" or "ANTLR for Dummies" anywhere. Any help 
> would be greatly appreciated.
>   I've also noticed that you have the lexer creating the tokens 
> LPAREN and RPAREN yet these tokens are not being referenced by the 
> parser, and the example doesn't accept them as valid input - if 
they 
> are not being used why are the there?
> 
> Thanks,
> -Kemmerzehl

Ignore previous message, after some sleep i conquered it. I must say 
it was alot easier than i thought. my parser now looks like this:

class CalcParser extends Parser;
options {
    buildAST = true;   // uses CommonAST by default
}
formula: expr SEMI!
    ;
expr:   mexpr (PLUS^ mexpr)*
    ;
mexpr
    :   atom (STAR^ atom)*
    ;
atom:   (INT|pexpr)
    ;
pexpr: LPAREN! expr RPAREN!
    ;

..simple!
Although, i am still a little confused as to why the LPAREN and 
RPAREN tokens were there in the first place, but that is beside the 
point.

Sorry to be a bother and thanks Terence this is really quite cool!
-Kemmerzehl


 

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