• Justin Johansson (23/23) Oct 12 2009 I'm working on a mini domain specific language (called say, MyDSL) which...
• Bill Baxter (18/26) Oct 12 2009 compiles to

Justin Johansson <see-body-of-message-for-name adam.com.au> writes:

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

Bill Baxter <wbaxter gmail.com> writes:

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 em=

bed MyDSL statements
 directly in a D source file in manner similar to string mixins. =A0It's u=

se might look something like this:
 void foo()
 {
 =A0 =A0MyDSLResult res =3D mixin( mydsl( `some-mydsl-statement-here`);
 =A0 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=3D1382

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