Would there be interest in a SERIOUS compile-time regex parser?

[Bill Baxter]

Reiner Pope wrote:
> Knud Sørensen wrote:
>> On Tue, 17 Oct 2006 12:23:33 -0700, Walter Bright wrote:
>>
>>> Don Clugston wrote:

> Three short answers:
> 
> 1. This would be easy to do (ie it is only heavy syntax sugar) for a 
> limited subset of the language (this subset would exclude reference 
> semantics).
> 
> 2. It would be possible to do for almost the entire language, but would 
> require a real interpreter at compile time, which means a fair bit more 
> work (but still possible and very appealing).
> 
> 3. Neither of these two mechanisms would be enough to do away with the 
> primary motivation for templates -- parameterised types. However, they 
> would remove the need for a Turing-complete template system.
...
> Both of these systems would incorporate a way of saying, 'evaluate this 
> at compile time', even if it were just as simple as declaring the 
> variable const, using it as a template parameter or in a static if:
> 
>   version (good) { const int N = 80; }
>   else { const int N = 16 }
>   const foo = sqrt(N); // foo is 4
>   static if (sqrt(foo) > 3) // that expression must be a compile-time 
> constant
>     alias ubyte MyByte;
>   else
>     alias byte MyByte;
>   List!(foo, MyByte) myList;
> 
> The main motivations for this are, (in decreasing order of importance):
>   - ability to use runtime functions for static if and template 
> parameters (where static if is important because of
>   - early catching of errors (eg incorrect regexes)
>   - efficiency (eg not having to compile the regex at runtime; also, 
> having cheap reflection at compile time)

This is exactly what I've been hoping someone would invent too.  It 
seems like the next logical step in template metaprogramming.  I think 
Walter's hip to the idea too.  Soon after the last big discussion about 
metaprogramming stuff and making it more like a true compile-time 
programming language, "static if" appeared.  I think that was something 
that Walter realized was "low-hanging fruit", which could quickly be 
implemented today and have a big impact now without waiting around till 
D 3.0.

So, I think it's vaguely on the D roadmap somewhere, it's just a huge 
undertaking and will take time.

--bb