"Kris" <fu@bar.com> wrote in message news:dnkk6s$2al1$1@digitaldaemon.com...
> Yes, that would be quite a feature :-)
>
> There was quite a bit of discussion early in the year about supporting regex-expressions as a first class citizens within the language.

Just a reminder that it isn't in the language for technical reasons, not because it's a bad idea.

> Doing so via a template could be a fine resolution.

That does sound like it'd be cool! I'd like to set it against David Abraham's C++ method of doing regex by using operator overloading and expression templates, a technique that is technologically marvelous but, in my not so humble opinion (!), is not aesthetically right.

On 12/13/2005 04:03 AM, Walter Bright wrote:
[snip]
> 
>>Doing so via a template could be a fine resolution.
> 
> 
> That does sound like it'd be cool! I'd like to set it against David
> Abraham's C++ method of doing regex by using operator overloading and
> expression templates, a technique that is technologically marvelous but, in
> my not so humble opinion (!), is not aesthetically right.

Could you provide a link to David's method, ... or are you referring
to spirit ( http://www.boost.org/libs/spirit/index.html ).  If you're
referring to spirit, then, IIUC, without the operator overloading, you'd
have to compose your regex with a complicated typedef:

  typedef alternative<term1,alternative<term2,term3> term1_2_or_3;

to represent the same regexp with operator overloading:

  term1 | term2 | term3

Isn't the 2nd form more aesthetic than the 1st form?

Walter Bright wrote:>

>> Doing so via a template could be a fine resolution.
> 
> That does sound like it'd be cool! I'd like to set it against David
> Abraham's C++ method of doing regex by using operator overloading and
> expression templates, a technique that is technologically marvelous but, in
> my not so humble opinion (!), is not aesthetically right.

Agreed.  Spirit shows a masterful grasp of C++ template syntax but the result is still a bit jarring (through no fault of David's).  A string-based regex parser could be great as a comparison, though it might be a bit much for an introductory article on D templates.


Sean

"Larry Evans" <cppljevans@cos-internet.com> wrote in message news:dnmcdl$rhd$1@digitaldaemon.com...
> On 12/13/2005 04:03 AM, Walter Bright wrote:
> [snip]
> >
> >>Doing so via a template could be a fine resolution.
> >
> >
> > That does sound like it'd be cool! I'd like to set it against David Abraham's C++ method of doing regex by using operator overloading and expression templates, a technique that is technologically marvelous but,
in
> > my not so humble opinion (!), is not aesthetically right.
>
> Could you provide a link to David's method, ... or are you referring to spirit ( http://www.boost.org/libs/spirit/index.html ).

My mistake. Eric Niebler created this, not David, here's the link: http://boost-sandbox.sourceforge.net/libs/xpressive/doc/html/index.html

> If you're
> referring to spirit, then, IIUC, without the operator overloading, you'd
> have to compose your regex with a complicated typedef:
>
>    typedef alternative<term1,alternative<term2,term3> term1_2_or_3;
>
> to represent the same regexp with operator overloading:
>
>    term1 | term2 | term3
>
> Isn't the 2nd form more aesthetic than the 1st form?

The problem is that with C++ (or D) operator overloading, one cannot:

1) invent new operators
2) change operator precedence
3) change operator binding

Therefore, one cannot create any form of operator overloading which looks like conventional regular expressions. They will, *necessarilly*, look like C++ (or D) expressions. I believe the resulting confusion creates more problems than it solves.

"Sean Kelly" <sean@f4.ca> wrote in message news:dnn1j7$1jup$1@digitaldaemon.com...
> Walter Bright wrote:>
>
> >> Doing so via a template could be a fine resolution.
> >
> > That does sound like it'd be cool! I'd like to set it against David Abraham's C++ method of doing regex by using operator overloading and expression templates, a technique that is technologically marvelous but,
in
> > my not so humble opinion (!), is not aesthetically right.
>
> Agreed.  Spirit shows a masterful grasp of C++ template syntax but the result is still a bit jarring (through no fault of David's).  A string-based regex parser could be great as a comparison, though it might be a bit much for an introductory article on D templates.

I agree it is not David's fault (although Eric Niebler created the regex library, not David http://boost-sandbox.sourceforge.net/libs/xpressive/doc/html/index.html), the results are crippled by the limitations of operator overloading.

David and I had argued the merits/demerits of this at some length on a private mailing list thread.

With regard to Spirit and Neibler's library, I agree with Walter's comments. Although it is cool that it can be done, the syntax is very ugly.  (As if regular expression syntax wasn't bad enough.)  D is poised to overcome these limitations.

-Craig

Craig Black wrote:
> If I understand correctly, D templates can take text as parameters.  I also understand that there are limitations as to the length of the text string. If this limitation could be eliminated, would it then be possible to generate highly-optimized source code from a regular expression at compile time?
> 
> Just a thought.
> 
> -Craig 

I have the beginnings of a library ("meta") designed for exactly those type of applications. Currently, the only usage of it is for D Dynamic Libraries, so it's currently living in the 'meta' subdirectory of the SVN repository for DDL on dsource. Currently, it only has mathematical and rudimentary string functions. There are a few workarounds for bugs in the current DMD compiler, but it's already obvious that the final code is going to be very clean and understandable.

BTW, the limit on the length of the text string only applies to the compile-time portion, and the limit is huge (about 2Kbytes). Although because you tend to use templates recursively, you run into the limit at much smaller sizes.
For regexp, you normally provide the string to be searched at compile time, and there's no limit on how long that can be. The regexp string is limited, but it should still be big enough to accomodate any regexp I've ever seen.

Craig Black wrote:
> If I understand correctly, D templates can take text as parameters.  I also understand that there are limitations as to the length of the text string. If this limitation could be eliminated, would it then be possible to generate highly-optimized source code from a regular expression at compile time?
> 
> Just a thought.
> 
> -Craig 
> 
> 
I'm not understanding clearly on this one. Are you asking for the ability to run a regexp on a string at compile time? Or to generate at compile-time an (optimized) code that will parse a given (constant) regexp in an arbitrary (non-constant) string?

-- 
Bruno Medeiros - CS/E student
"Certain aspects of D are a pathway to many abilities some consider to be... unnatural."

> I'm not understanding clearly on this one. Are you asking for the ability to run a regexp on a string at compile time? Or to generate at compile-time an (optimized) code that will parse a given (constant) regexp in an arbitrary (non-constant) string?

It would be ideal to be able to generate optimized code at compile-time from a regular expression.  The regular expression could be a parameter to a D template.  This template would be able to parse a an arbitrary string at run-time using this optimized code.  Does that make sense?

-Craig

Craig Black wrote:
>>I'm not understanding clearly on this one. Are you asking for the ability to run a regexp on a string at compile time? Or to generate at compile-time an (optimized) code that will parse a given (constant) regexp in an arbitrary (non-constant) string?
> 
> 
> It would be ideal to be able to generate optimized code at compile-time from a regular expression.  The regular expression could be a parameter to a D template.  This template would be able to parse a an arbitrary string at run-time using this optimized code.  Does that make sense?
> 
> -Craig 
> 
> 
Yup, got it.

-- 
Bruno Medeiros - CS/E student
"Certain aspects of D are a pathway to many abilities some consider to be... unnatural."