Re: callbacks, #define/typedef tricks

[Hans Aberg]

On 4 Jun 2009, at 15:37, Kynn Jones wrote:

> Hi.  I want to write a "base parser" for JSON that can be easily  
> customized
> to generate objects in any interpreted language (such as Perl or R)  
> whose
> underlying implementation is in C.
...
> Does anyone know of any Bison parser (with a publicly
> accessible source code, and preferably written in C) that attempts  
> this sort
> of pluggable polymorphic callback architecture?

You might inquiry in the Usenet newsgroup comp.compilers.

>  (Yes, I definitely want to
> stay with C, rather than C++.)

Bison is now quite good at C++, see
  http://lists.gnu.org/archive/html/help-bison/2009-05/msg00040.html

> The idea is that I need a good way to plugin callbacks corresponding  
> to the
> various "parser events".  E.g. I want to be able to write rules like
>
> %token <toktext> __INTEGER __FLOAT __STRING __BOOLEAN __NULL
> %type  <THINGIE> value object array
> ...
> value:
>        __INTEGER       { $$ = (CALLBACK_FOR_INTEGER)($1); }
>      | __FLOAT         { $$ = (CALLBACK_FOR_FLOAT)($1); }
>      | __STRING        { $$ = (CALLBACK_FOR_STRING)($1); }
>      | __BOOLEAN       { $$ = (CALLBACK_FOR_BOOLEAN)($1); }
>      | __NULL          { $$ = (CALLBACK_FOR_NULL)(); }
>      | object
>      | array
>      ;
>
> For each target language (R, Perl, Python, etc.), a different set of
> callbacks would be plugged in.  There are two main objstacles, as I  
> see it.
> First, the mechanics of plugging in these callbacks in a way that is
> straightforward and safe.  Second, the fact that the return types  
> for all
> these callbacks will differ from one target language to the next, so  
> THINGIE
> would have different meanings depending on the target language.

From what I can see from <http://en.wikipedia.org/wiki/JSON> you  
somehow want to create these objects in other languages, right? One  
way might be to use the Bison generated top generate an AST. The it is  
not difficult to reverse that to pretty-print that AST into other  
languages. In that example on that page, you might parse the Object  
into C++ std::map. Then print out that object in other languages.

  Hans