compile-time regex redux

[Sean Kelly]

Walter Bright wrote:
 >
> At some point, this will prove a barrier to large scale use of this 
> feature.

I agree, though I'm not sure this feature will see large scale use 
either way.  Template metaprogramming is still very uncommon outside of 
library code.

> Andrei suggested using compile time regular expressions to shoulder much 
> of the burden, reducing parsing of any particular token to one 
> instantiation.
> 
> The last time I introduced core regular expressions into D, it was 
> soundly rejected by the community and was withdrawn, and for good reasons.
> 
> But I think we now have good reasons to revisit this, at least for 
> compile time use only. For example:
> 
>     ("aa|b" ~~ "ababb") would evaluate to "ab"
> 
> I expect one would generally only see this kind of thing inside 
> templates, not user code.

I agree that this would eliminate the need for a lot of template library 
code and would speed compilation for applications using such techniques. 
  I am still unsure whether this is sufficient to warrant its inclusion 
to the language, but I'm not strongly opposed to the idea.  However, for 
this to be useful I'd like to reiterate that I would want some way to 
continue parsing after the match point.  The most obvious would be to 
return an index/string pair where the index contains the position of the 
match in the source string, or as you mentioned, perhaps an array 
consisting of three slices: the source string preceding the match, the 
match itself, and the source string following the match.


Sean