I'm working on a mini domain specific language (called say, MyDSL) which compiles to
(generates) D code and am thinking that it might be nice to be able to embed MyDSL statements
directly in a D source file in manner similar to string mixins.  It's use might look something like this:

void foo()
{
    MyDSLResult res = mixin( mydsl( `some-mydsl-statement-here`);
   now_do_something_with( res);
}

There was a question similar to this somewhere around DM newsgroups a while back
(regarding embedding Scheme I think?), but as I recall there wasn't any definitive
feedback on the idea.  Also, being still relatively new to D, there are a number of possibly
related threads on the NGs that have gone over my head, so please bear with me if this
has been dealt with before.

My specific question is:

What would be the best way of embedding some DSL code into D source code?
Is there some cool feature of D (that I don't yet know about) that lets you employ
string mixins for this purpose, or would one need to write a preprocessor to grok D
source code in order to compile in the embedded DSL code?

The alternative is just to compile/translate MyDSL code into a standalone D source module and just run with that .. though the idea of actually embedding directly into D does have some real appeal (at least to me).

Hope this makes sense and, as usual, thanks for all help,

-- Justin Johansson

On Mon, Oct 12, 2009 at 8:24 AM, Justin Johansson <see-body-of-message-for-name@adam.com.au> wrote:
> I'm working on a mini domain specific language (called say, MyDSL) which compiles to
> (generates) D code and am thinking that it might be nice to be able to embed MyDSL statements
> directly in a D source file in manner similar to string mixins.  It's use might look something like this:
>
> void foo()
> {
>    MyDSLResult res = mixin( mydsl( `some-mydsl-statement-here`);
>   now_do_something_with( res);
> }

In theory that can work, and I think there have been some proofs of
concept along those lines.
But the problem is that you have to manage to write a translator for
your DSL using only the subset of D that works at compile time.

And I believe there are still memory leaks in D's CTFE engine.  So if CTFE expressions get too complex the compiler will slow to a crawl and eventually crash.  Ah yes, here it is: http://d.puremagic.com/issues/show_bug.cgi?id=1382

I don't know of any other way of implementing a DSL in D, other than using a standard run-time parser tool, which is probably the more sane way to go here.  Unless your DSL is really simple or you just love a challenge.

--bb