Re: optional nonterminal symbols

[Arkadius Nowakowski]

Thank you! 

I've pulled the optional nonterminal to the same lvl 
as the optional terminal tag2 and modified the grammar.

Best regards.
Ting

On Mon, Nov 21, 2005 at 06:42:19PM +0100, Hans Aberg wrote:
> 
> On 21 Nov 2005, at 12:49, Arkadius Nowakowski wrote:
> 
> >Hi,
> >
> >I've got a gramar like this:
> >
> >%{
> >%}
> >
> >%start start
> >
> >%token START END TAG1_1 TAG1_2 TAG2
> >
> >%%
> >
> >start: START tag1 END
> >     | START tag1 tag2 END
> >;
> >
> >tag1: tag1_1 {}
> >     | tag1_1 tag1_2 {}
> >;
> >
> >tag1_1: TAG1_1 {}
> >;
> >
> >tag1_2: /*empty*/ {}
> >     | TAG1_2 {}
> >;
> >
> >tag2: TAG2 {}
> >;
> >
> >%%
> >
> >As you can see, the nonterminal symbols "tag2" and the sub symbol
> >"tag1_2" are optional. Of course bison tells me, that there is a
> >reduce/reduce conflict. Is there a way to change the bison source
> >achieving the same goal?
> 
> You need to somehow merge together the two empties, if you want to  
> avoid the conflict. Strictly speaking, this is not a grammar problem,  
> but an action problem (of the parse tree). Think of a product that  
> you expand: (A | epsilon)(B | epsilon) = A B | A | B | epsilon. Here,  
> on the RHS, there is only one empty (= epsilon) grammar symbol.
> 
>   Hans Aberg
> 
> 

-- 

Arkadius Nowakowski

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