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

From: Hans Aberg
Subject: Re: A polymorphic YYSTYPE for C++ (instead of the %union)
Date: Fri, 15 Jun 2007 20:08:20 +0200

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

Thanks for the patch that you proposed in
< 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

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