eval() (Was: One more update on d-programming-language.org)

[Nick Sabalausky]

"Philippe Sigaud" <philippe.sigaud at gmail.com> wrote in message 
news:mailman.214.1284496545.858.digitalmars-d at puremagic.com...
> On Tue, Sep 14, 2010 at 17:01, Andrei Alexandrescu <
> SeeWebsiteForEmail at erdani.org> wrote:
>>
>>  I think we'll move forward with that one. I'll start working on the
> content. Ideas for good tutorial examples?
>>
>
> Maybe more examples of what's interesting me right now than tutorials, but
> who knows?
>
> * executing command-lines instructions from a D program. Theme: file I/O, 
> OS
> interaction.
> An interesting example is having a script that loads a D file, modifies 
> its
> source, asks for DMD to compile it and then runs it and get its result. It
> could be the first brick to get a REPL / idmd (interactive dmd). Maybe 
> more
> a [challenge] subject than a tutorial example?
>

One thing that could be used for that is the eval() function I've recently 
added to my SemiTwist D Tools library:

http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/util/process.d

Example:
-----------------------------
import semitwist.util.all;
void main()
{
    auto x = eval!int(q{ return 21 * 2; }); // String can be 
runtime-generated
    assert(x == 42);

    eval!void( q{ writeln("Hello World"); }, q{ import std.stdio; } );
}
-----------------------------

It does require dmd and rdmd to be on the path.

I hadn't posted anything about it before because it's still 
rough-around-the-edges and needs polish. For instance, most of the useful 
phobos modules aren't imported by default, and it doesn't yet support 
returning string/wstring/dstring - you have to return char[]/wchar[]/dchar[] 
instead and then convert back to string/wstring/dstring (but that shouldn't 
be too hard to fix). Also, on Windows it requires a patched version of rdmd, 
which is included with the library ( 
http://www.dsource.org/projects/semitwist/browser/trunk/rdmdAlt.d ) but eval 
doesn't yet compile it if it isn't already compiled, and it assumes it's on 
the path (I've already solved both of these in the included stbuild program, 
I just need to move the solution over into the general library). My ultimate 
goal with this is to hack up DMD just enough to make it work at compile-time 
(so that *any* arbitrary code can be run at compile-time, albiet more 
awkwardly and with much more overhead than ordinary CTFE).