Re: how do i implement double-dispatching?

[Stephen Leake <stephen_leake@acm.org>]

cl1motorsports <cwlambert76@yahoo.com> writes:

> On Sat, 20 Dec 2003 10:56:07 +0100, Martin Krischik wrote:
> 
> > Have you considered to send the C file thrue the C preprocessors
> > and convert the output? #if #define etc. pp. will be cone by then.
> 
> What's the fun in that? Seriously though, the most common preprocessor is
> the one that comes with gcc, and it puts alot of non standard C stuff in
> its output. 

Hmm. I never noticed anything that was not in the ANSI C standard. Are
you sure it is truly not in that standard? Or is it just something you
are not familiar with? In any case, you can disable any non-standard
stuff by specifying -ansi.

> That is one reason I didn't want to do that. Another reason is
> because some people may want to convert a whole project and want to
> keep the preprocessed code. 

I think you mean "translate the preprocessor statements into Ada, to
preserve structure". That is a good idea.

> I already have some ideas on this
> 
> #define FOO
> Foo : constant Boolean := True
> 
> #define FOO "i'm a string"
> Foo : constant String(1..12") := "i'm a string";
> 
> #define FOO 12
> Foo : constant := 12;
> 
> #define MAX(a,b) (a < b) b ? a;
> generic
> 	type blah is <>;
> function Max(a : blah; b : blah) return blah is
> begin
> 	if (a < b) then
> 		return b;
> 	else
> 		return a;
> 	end if;
> end Max;
> function 
> 
> that's just a few examples. 

This will work for many common uses of the preprocessor. Of course, it
will not be possible for _all_ uses of the preprocessor. But then your
translator can either run the C preprocessor and use the output, or
issue an error about untranslatable code.

> I also want to use the define statements to be able to produce
> generic packages. I've got a direct conversion for most types of
> #define statements (i think) except ones with the stringize and
> concatination operators, and the ones that are just down right messy
> (garbage in garbage out). 

Right. Those should be re-written anyway :).

-- 
-- Stephe