04-Dec-2013 20:22, Andrei Alexandrescu пишет:
On 12/4/13 7:06 AM, H. S. Teoh wrote:
On Wed, Dec 04, 2013 at 04:23:59AM +0100, bearophile wrote:
Joshua Niehus:
This would make for a good blog post/wiki article. Does one
already exist?
If you have a AST macros like in Julia language, I think you can
write something like:
@setExpr(a ∪ (b ∩ c));
The main difference is that the compiler gives you a tree in the
macro to work on, instead of a string to parse and munge.
[...]
The problem with having the compiler parse it is that it has to be in a
syntax understood by the compiler. If your DSL needs a radically
different syntax, it won't work (e.g., regex: how is the compiler to
know '+' is a postfix operator instead of an infix one?).
By having a compile-time string as input, you have maximum flexibility.
It's essentially writing a mini-compiler embedded in D, because it runs
in CTFE.
Yah, my thoughts exactly. Looks like we're in a sweet spot there.
I'll just add a bit of my experience on this.
The coolest side of things is that you get to code a mini-compiler that
has a very nice backend - D code. More then that you get optimizer and
such for free. Then you only do the fun stuff - your frontend, and if it
wasn't for CTFE speed/stability the experience is _very_ pleasant.
Compare that with writing a fully fledged JIT compiler for say, regex
patterns. Don't forget to account that you'd need to port it to X
architectures times Y OS ABIs and generate code of at least moderate
quality.
JIT would have the benefit of being usable for patterns not known ahead
of time though.
--
Dmitry Olshansky
