Re: %union ... {

[Hans Aberg]

On 19 Jun 2006, at 07:49, Paul Eggert wrote:

> In this particular case, since it's not too much trouble, let's worry
> it, since we want Bison to be a drop-in replacement for BSD Yacc (even
> for careless users :-).
>
> > If we want to set the user really free, then let's extend the grammar
> > with more than just ID, for instance a STRING, or even BRACED_CODE.
>
> I don't see why that would be useful, and in the case of BRACED_CODE
> it might even lead to weird behavior by Bison if the user forgets the
> second % in "%union { ... } %{ .... %}".  Since this is purely for
> compatibility I think that all we really need to support is what's
> used by BSD Yacc + C grammars, or perhaps BSD Yacc + C++ if some
> people actually use that combination.  If you think it unlikely that
> C++ programers use "%union foo::bar {...}" then let's just support
> single identifiers; that should be enough.

First, if the question is of just giving the implemented C++ 'union'  
a name, I think that, when using the C++ 'namespace' construction,  
one has to write:
  namespace <name1> {
    ...
    union <name2> {....};
    ...
  }
to get the name1::name2 name. Thus, it is not needed as a part of % 
union.

Second, as a preparation for other languages, it suffices that
  %union <label> {...};
defines a M4 macro name derived from <label>, because then, when the  
code placemenety version of %define becomes ready, one can write
  %define <label> {<code>}
Or, if Bison always defines a macro say UNION_NAME, one can write:
  %union {...};
  %define UNION_NAME {<code>}
This simplifies the implementation of the Bison .y grammr.

  Hans Aberg