[antlr-interest] Gramar without semicolon

[Joan Pujol]

Thanks a lot. Is exactly what I need.

Cheers,

On Wed, 28 Jul 2004 14:43:43 -0400, jbb at acm.org <jbb at acm.org> wrote:
> Greetings!
> 
> You wrote:
> ......snip....
> >I make a simple case with only two instructions an if
> >and an assignament:
> >
> >instructions: (instruction)+;
> >instruction: inst_if | inst_assig;
> >inst_if: IF expr THEN (NL)* instructions (ELSE (NL)*
> >instructions)? ENDIF ((NL)+ |SEMICOLON instruction);
> >inst_assig: IDENT ASSIG expr ((NL)+ |SEMICOLON
> >instruction);
> >
> >This I think that works quite well and recognizes
> >thinks like
> >
> >IF expr THEN inst1;inst2
> >ELSE  inst1
> >END IF
> >
> >But it can't recognize
> >IF expr THEN inst1 ELSE inst2 END IF
> >
> >And I don't know how to manage this, I think that I've
> >to use semantic predicates but I am a little confused.
> 
> The (NL)+ phrase near the end of both the inst_if and the inst_assig
> rules mean that a NL is always required to terminate an instruction
> phrase.
> 
> But you want the NL to be optional sometimes (e.g. at the end of the
> then phrase and at the end of the else phrase).
> 
> Here is a grammar fragment that makes the NL optional - and maybe
> making it optional in too many places in the rest of your grammar...
> 
> program :
>         instruction_block EOF
>     ;
> 
> instruction_block :
>         single_line ( (NL)+ ( instruction_block )? )?
>     ;
> 
> single_line :
>         instruction ( SEMICOLON instruction )*
>     ;
> 
> instruction :
>         inst_if | inst_assig
>     ;
> 
> inst_if :
>         IF expr THEN (NL)* instruction_block
>         ( ELSE (NL)* instruction_block )?
>         ENDIF
>     ;
> 
> inst_assig :
>         IDENT ASSIG expr
>     ;
> 
> Hope this helps....
>         John B. Brodie (jbb at acm.org)
-- 
Joan Jesús Pujol Espinar


 
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