[antlr-interest] Epsilon productions and end of file

[Marcin Rzeznicki]

----- Wiadomosc oryginalna ----- 
Od: "Arnar Birgisson" <arnarb at oddi.is>
Do: <antlr-interest at yahoogroups.com>
Wyslano: 18 grudnia 2003 14:22
Temat: RE: [antlr-interest] Epsilon productions and end of file


> Hello Marcin,
>
> Could you post a portion of your ANTLR grammar?

Of course, this grammar is meant to be well-formed logical formulae grammar.
I have eliminated left recursion, also performed factorization of the
grammar. It is :
F->DF'
F'->ifthen F | epsilon
D->CD'
D'->or CD' | epsilon
C->NC'
C'->and NC' | epsilon
N->not N | P
P->var | (F)

In ANTLR it is like:
formula
 returns [Formula f]
 { f = null; Formula f1; Formula f2; }
  :  f1=disjunction f2=sformula
   {
   if (f2!=null) {
    f = new Formula();
    f.setType(CONDITIONAL);
      f.attachLeft (f1);
    f.attachRight (f2);
   } else
    f = f1;
   }
  ;

sformula
 returns [Formula f]
 { f = null; }
  :  IF_THEN f=formula
                | //epsilon
  ;

disjunction
 returns [Formula f]
 { f = null; Formula f1; Formula f2;}
  :  f1=conjunction f2=sdisjunction
   {
   if (f2!= null) {
    f = new Formula();
    f.setType(DISJUNCTION);
    f.attachLeft (f1);
    f.attachRight (f2);
   } else
    f = f1;
   }
  ;
and so on

>
> Btw: Are you eliminating left-recursion by adding F'? If so it's
> convenient to use ANTLR-specific syntax instead (the ? or + operators).

What do you mean by using ? and + instead eliminating left recursion? I
don't quite catch it. :-)

-- 
Pozdrawiam
Marcin Rzeznicki





 

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