Re: [PATCH] more on prologue alternatives

[Paolo Bonzini]

> > What if the user doesn't have a %union?
> > You place your %{...%} or %header { ... } block *after the %%*, in the grammar
> > section.
>
> You said that maps to before the header or the beginning of the header, so
> that wouldn't work, right?

No, after %% and after %union is the same.  But I may as well withdraw
my patch, read on.

> > Java will not use %union in fact, but it needs to have "%{...%}"
> > after the %% to declare parser methods.
>
> As I understand it (but I'm not a Java expert), before vs. after and start
> vs. end is pretty much irrelevant in Java.  That is, the compiler figures
> out forward references for you.  So, as far as I can tell, you only need
> to care about header vs. code file, right?

Well, you could say that you need only two instead of three: in my case it
is "outside the parser class" (e.g. for imports) and "inside" (for
methods used in the actions).  But they don't really map to header/code,
so I'm using %{...%} respectively before/after %%.

> > >   %start-header { #include "type1.h" }
> > >   %union { type1 field1; }
> > >   %destructor { type1_destroy ($$); } <type1>
> > >
> > >   %start-header { #include "type2.h" }
> > >   %union { type2 field2; }
> > >   %destructor { type2_destroy ($$); } <type2>
>
> Modularity.  I think the user should have more flexibility in how to
> organize his grammar file.  I don't see the above as scattered.  I see it
> as organized by type.

That's a different point of view.  I can't but accept that there are
other points of view! :-)

> Just out of curiosity, how would the following proposal
> (mentioned somewhere in that thread) work for you?  We would make the
> following changes to the %*-header directives:
>
> 1. Change %after-header{...} to %code{...}.  This is where you put most
> code for the code file.
>
> 2. Change %end-header{...} to %header-code{...}.  This is where you put
> most code for the header file.

So far so good.

> 3. Change %start-header{...} to %type-code{...}.  For C/C++ users, this is
> the right place to put any code that is required by YYSTYPE or YYLTYPE. 
> You probably don't need it in Java, but you could use it if you'd like to
> organize your output.

I don't like the %type-code name (constructive criticism in a couple
of paragraphs!).

> 4. Remove %before-header entirely.  We're not sure it's actually
> necessary.

I would put #include directives for the parser
there in C (e.g. <stdlib.h>), since %before-header IIRC is just good
old %{...%}.  But in the end putting them in %after-header wouldn't be
a problem, right?

For Java I need only one of %start-header and %before-header, and only
one of %end-header and %after-header.  I'd choose the one that is more
language-neutral, so I'm very much okay with just renaming the
directives.

A renaming proposal working for me would be %after-header -> %code, and
%before-header -> %prolog, and likewise %header-code and %header-prolog.
This, plus letting these appear in the grammar section, would be just
perfect.  I think it would keep the "coherency/symmetry" idea of my
patch, and all the flexibility of CVS Bison.

Paolo