Understanding regexes (Was: Re: DMD 0.147 release)

[Stewart Gordon]

Georg Wrede wrote:
> Walter Bright wrote:
>> "Wang Zhen" <nehzgnaw at gmail.com> wrote in message 
>> news:dt49iv$2hm5$1 at digitaldaemon.com...
>>
>>> Although syntactically correct, MatchExpression in
>>> StaticIfCondition or StaticAssert do not compile. For example:
>>>
>>> void main(){static if(!("" ~~ "")){}static assert("" ~~ "");}
>>>
>>> Is this intended or an unimplemented feature?
>>
>> The problem is that getting it to work requires the compiler itself
>> to understand regular expressions. Currently, it does not.
> 
> Intriguing. I'd sure love to hear more about this.
> 
> I take it understanding regular expressions is much more than just 
> compiling them? (Like what the runtime does, or Perl, etc.?)

A problem is that there are a number of dialects of regexp.  The spec 
doesn't seem to indicate which dialect is being used.

Among the differences between them is whether subexpressions are 
parenthesised by \(...\) or simply (...).  Another issue is whether we 
expect implementations to support the Unicode extensions to regexps 
described here

http://www.textpad.info/forum/viewtopic.php?t=4778

No doubt there are other differences....

Whichever we choose, the behaviour of using std.regexp directly, ~~ 
evaluated at runtime and ~~ evaluated at compiletime must be consistent. 
  But that isn't hard - the compiler would just call the same code that 
std.regexp uses.

Stewart.

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