[antlr-interest] Re: native rules?

Alexey Demakov demakov at ispras.ru
Fri Oct 22 02:55:58 PDT 2004


'-' '\n' will be processed incorrectly

Regards,
Alexey

> Wolfgang--
> 
> Why not
> 
> COMMENT
>     :
>     "--"
>     (   ~( '\n' | '-' )
>     |   '-' ~'-'
>     )*
>     ( "--" )?  // NEWLINE or whatever picks up '\n'
>     ;
> 
> The greedy/non-greedy stuff is much overused.
> 
> --Loring
> 
> 
> --- In antlr-interest at yahoogroups.com, "whaefelinger"
> <ora.et.labora at w...> wrote:
> > 
> > Hello,
> > my language allows a comment to start with "--" and end with ither "-
> > -" or with an EOL character ('\n'). So I wrote this two rules:
> > 
> > protected
> > UNTIL_END_OF_COMMENT
> >     : ( options {greedy=false;} : . )* ("--"|"\n")
> >     ;
> > 
> > COMMENT
> >     : "--" UNTIL_END_OF_COMMENT
> >     ; 
> > 
> > ANTLR warns me then (as  written  in the manual)  about  "nongreedy 
> > block may exit incorrectly due to limitations of linear approximate 
> > lookahead [..].
> > 
> > Here's a snippet of what ANTLR generates for rule 
> > UNTIL_END_OF_COMMENT
> > 
> >  _loop53:
> >  do {
> >    // nongreedy exit test
> >    if ( (LA(1)=='\n'||LA(1)=='-') && (true)) 
> >       break _loop53;
> >    // ...
> >  } while (true);
> > 
> > Hmm, that's almost fine. If I just could rewrite this as 
> > 
> >  _loop53:
> >  do {
> >    // nongreedy exit test
> >    if ( LA(1)=='\n' || (LA(1)=='-' && LA(2)=='-') ) 
> >       break _loop53;
> >    // ...
> >  } while (true);
> > 
> > then I would be done (BTW: I do have the feeling that I can attack 
> > the problem with a predicate - but haven't found the right solution 
> > yet).
> > 
> > Now I was wondering whether ANTLR would allow me to tweak in my own 
> > handcraftet rules? What I'm thinking about is something like:
> > 
> > protected UNTIL_END_OF_COMMENT ;
> > 
> > That means: If a  protected  rule with no "body" exists then ANTLR 
> > will not generate a method but will rather assume that such a method 
> > already exists.
> > 
> > This seems trivial to implement but does not exist. Therefore I 
> > assume that there must be specific reasons for not having this 
> > native rule escape. 
> > 
> > Can someone give me a hint on this??
> > 
> > 
> > Thanks,
> > Wolfgang.
> 
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 



 
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