Ellery Newcomer wrote:
On 04/20/2010 10:17 AM, Don wrote:
I don't see anything particularly ugly or hacky about CTFE code, like
the code below:
int greater(int a, int b) {
if (a>b) return a;
else return b;
}
int [ greater(short.max/3, 515) ] foo;
It isn't. Things don't get ugly until you hit the relatively low ceiling
of what ctfe can handle. I don't pay much attention to where that
ceiling is, but I am aware that the situation has been improving mostly
due to your efforts, and I appreciate that.
So far, all my ctfe code is code generation for string mixins, and it's
fairly modest stuff, to the point where a simple string formatting
function could probably take care of a fair portion of the problem. It's
just that I don't know of any. (I'm in D1/Tango land)
The other half of the problem is parsing input strings for simple dsls.
Having to write out a lexer/parser from scratch just sucks regardless,
and writing it in ctfe code, which isn't allowed composite data
structures (last I checked) is really not worth doing.
Now that it can do struct member functions and delegates, it's possible
to do fairly sophisticated things in CTFE. Unfortunately the two killer
bugs (bug 1330 and 1382) still aren't fixed, so the frustration level is
still pretty bad. We're still a few releases away from getting a fix for
those ones.
I think D fails
on its promise here, where it says "with string mixins you can create
your own dsls", but then provides no additional support.
Yes, the two CTFE bugs I mention are blockers. Once they're fixed, it
will be fairly simple to add support for classes, exceptions, and nearly
everything else.
As ctfe support matures, I dream of a full-fledged parser generator that
can be evaluated at compile time, although that's way more heavy duty
than what most people will need.
Another idea is something more on the lines of haskell's parsec, which
provides building blocks for common tokens, etc. I don't know much about
it, though.
Even compile time regular expressions would be better than nothing..
And whatever it is, it needs to be in the standard library.
Exactly.
