Re: A polymorphic YYSTYPE for C++ (instead of the %union)

[Hans Aberg]

On 15 Jun 2007, at 18:12, Paul Eggert wrote:

> Thanks for the patch that you proposed in
> <http://lists.gnu.org/archive/html/bison-patches/2007-06/ 
> msg00000.html>.
> I don't use C++, so you'll have to bear with me on some dumb
> questions.  Perhaps some other contributor who knows C++ well can also
> chime in.
>
> * How much is this patch tied to Boost?  Can it be used easily with  
> other
>   C++ libraries?
>
> * What sort of documentation should appear in the Bison manual?
>
> * Why is there a limitation on what types can appear?  (They can't
>   have angle brackets, apparently.)  Can this limitation be removed?

If one cannot use the type system that comes with %union, there is  
not change needed: I have used a standard C++ polymorphic class  
hierarchy for years. The only problem was some code placement, but  
has has been fixed with the extension of %define that Akim fixed.

Akim has been thinking of variants as typed replacement of %union.  
Then I think the problem is with the default actions, which no longer  
can be collected to a single entry in the parser "switch" statement.  
And if this part is being fixed, one can just well just introduce a  
M4 macro, admitting variants as well as a standard C++ polymorphic  
hierarchy, I think.

  Hans Aberg