Re: [PATCH] more on prologue alternatives

[Joel E. Denny]

On Tue, 3 Oct 2006, Paolo Bonzini wrote:

> 3) %{...%} maps to before header if it is seen before %union or after the
> first %%, otherwise it maps to after header.
> 
> 4) %header { ... } maps to beginning of header if it is seen before %union or
> after the first %%, otherwise it maps to after header.

But the dependence on the %union position is one of the key problems I was 
trying to eliminate.  I don't have time to examine your patch right now, 
but, if I understand the explanation above, the only way to do the 
equivalent of %end-header or %after-header is to have a %union.  What if 
the user doesn't have a %union?  It doesn't make sense that %union should 
matter.

Also, I'd like to see this kind of grammar organization work:

  %start-header { #include "type1.h" }
  %union { type1 field1; }
  %destructor { type1_destroy ($$); } <type1>

  %start-header { #include "type2.h" }
  %union { type2 field2; }
  %destructor { type2_destroy ($$); } <type2>

This should be allowed in the definitions or rules section.  If you change 
%start-header to %header under your proposal, it won't work.

Thanks for your interest in this problem.  Maybe you'd like to catch up 
with our latest discussion starting here:

  http://lists.gnu.org/archive/html/bison-patches/2006-09/msg00048.html