Re: proposal: simplify prologue alternatives into %code

[Paolo Bonzini]

> Then a special directive %typed triggering the Bison type system may not 
> be required, as this if %cast appears, one knows the .y file is typed. 
> Another way would that %cast can appear, but is not used, unless a 
> %typed also appears.

%typed is unnecessary if a <foo> tag is used in the grammar.  While now 
<foo> is always a member name, it will be a type name in Java and it 
would be a type name also in C++ if one wants to expand

%type<some_class>  xyz

to {static,dynamic}_cast<type>(*var).

In fact, something aking to your %typed is already exported to the 
skeletons as b4_tag_seen_flag, where we have

m4_if(b4_tag_seen_flag, 0,
[[typedef int YYSTYPE;
# define YYSTYPE_IS_TRIVIAL 1]]

I'm also against a new directive such as your %cast, since Bison already 
has too many and -- in this particular case -- a simple %define is all 
that is needed.

> The implementation of %typed would be the same as %union

It would be interesting if you took a look at the implementation of 
%union (which is just a "code muscle", equivalent to something like 
"%code stype") before making this imperscrutable statement. :-)

Paolo