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Re: Good use of bitwise NOT "~" or unnecessary obfuscation?

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Patricia Shanahan wrote:

> Scott Sauyet wrote:
>> I personally can't see it.  My example was intentionally verbose and
>> as explicit as I could comfortably be, so as to remove the regex
>> terseness factor from the equation and see if Tim still had
>> objections.  The objections many have to Perl are similar to one main
>> objection to regexes: they are often simply unreadable: write-only
>> code.  Your abbreviations are shortened enough to no longer be clear.
>> None of the keywords except "OR" are really obvious.  It really
>> doesn't look much clearer to me than `/^\s+|\s+$/g `.
> 
> I think there is a significant difference between Perl and regex. In
> Perl, terseness is a choice. One can use meaningful identifiers, white
> space, and comments. I have written maintainable Perl code.
> 
> In regex, there is no option for meaningful identifiers, or, as Gene
> pointed out, white space. Comments have to be either before or after the
> entire regex, not interleaved with it.

Apples and oranges.  Perl is a *programming language*; regular expressions 
are part of a *technique* (pattern matching) usable *in* programming 
languages.

And apparently you are not aware that *especially* Perl's implementation of 
regular expressions, and Perl-Compatible Regular Expressions (PCRE) as 
supported by e.g. PHP, allow what you are asking for with the `x' 
(PCRE_EXTENDED) flag:

  my $leadingOrTrailingWhitespace =
    /
      ^    # (start of input
           # followed by
      \s+  # at least one whitespace)
      |    # or
      \s+  # (at least one whitespace
           # followed by
      $    # end of input)
    /x;

In PHP (with PCRE):

<?php
  $leadingOrTrailingWhitespace =
    '/
       ^    # (start of input
            # followed by
       \s+  # at least one whitespace)
       |    # or
       \s+  # (at least one whitespace
            # followed by
       $    # end of input)
     /x';

  $s = preg_replace($leadingOrTrailingWhitespace, '', '  foo  ');
?>

In ECMAScript implementations (with JSX:regexp.js [1], revisions 272 and 
later):

  var leadingOrTrailingWhitespace = new jsx.regexp.RegExp(
    [
      "^     # (start of input",
      "      # followed by",
      "\\s+  # at least one whitespace)",
      "|     # or",
      "\\s+  # (at least one whitespace",
      "      # followed by",
      "$     # end of input)"
    ].join("\n"),
    "x"
  );

or (standards-compliant since Ed. 5, proprietarily available before):

  var leadingOrTrailingWhitespace = new jsx.regexp.RegExp(
    "^     # (start of input \n\
           # followed by \n\
     \\s+  # at least one whitespace) \n\
     |     # or \n\
     \\s+  # (at least one whitespace \n\
           # followed by \n\
     $     # end of input",
    "x"
  ); 

> I would be much happier if one could build regular expressions up in
> pieces, using identifiers to reference components:
> 
> leadingSpaces = /^\s+/
> trailingSpaces = /\s+$/
> leadingOrTrailingSpaces = /{leadingSpaces} | {trailingSpaces}/
> 
> s = s.replace(/{leadingOrTrailingSpaces}/g, "");

Built-in (ECMA-262-5.1, §15.10.4):

  var leadingSpaces = "^\\s+";
  var trailingSpaces = "\\s+$";
  var leadingOrTrailingSpaces =
    new RegExp(leadingSpaces + "|" + trailingSpaces, "g");

  var s = s.replace(leadingOrTrailingSpaces, "");

or

  var leadingSpaces = "^\\s+";
  var trailingSpaces = "\\s+$";
  var leadingOrTrailingSpaces =
    new RegExp([leadingSpaces, trailingSpaces].join("|"), "g");

  var s = s.replace(leadingOrTrailingSpaces, "");

(You can find more examples in JSX:regexp.js where I am building the 
expressions to implement, for example, Unicode character property classes.)

With JSX:regexp.js (revisions 275 and later):

  var leadingSpaces = /^\s+/;
  var trailingSpaces = /\s+$/;
  var leadingOrTrailingSpaces =
    jsx.regexp.concat(leadingSpaces, "|", trailingSpaces);

  s = s.replace(new jsx.regexp.RegExp(leadingOrTrailingSpaces, "g"), "");

or

  var leadingSpaces = /^\s+/;
  var trailingSpaces = /\s+$/;
  var leadingOrTrailingSpaces = leadingSpaces.concat("|", trailingSpaces);

  s = s.replace(new jsx.regexp.RegExp(leadingOrTrailingSpaces, "g"), "");

I am considering

  var leadingSpaces = /^\s+/;
  var trailingSpaces = /\s+$/;
  var leadingOrTrailingSpaces =
    jsx.regexp.alternate(leadingSpaces, trailingSpaces);

  s = s.replace(new jsx.regexp.RegExp(leadingOrTrailingSpaces, "g"), "");

and

  var leadingSpaces = /^\s+/;
  var trailingSpaces = /\s+$/;
  var leadingOrTrailingSpaces = leadingSpaces.alternate(trailingSpaces);

  s = s.replace(new jsx.regexp.RegExp(leadingOrTrailingSpaces, "g"), "");

What do you think?


PointedEars
___________
[1] 
<http://PointedEars.de/websvn/filedetails.php?repname=JSX&path=%2Ftrunk%2Fregexp.js>
<http://PointedEars.de/scripts/test/regexp>
-- 
Sometimes, what you learn is wrong. If those wrong ideas are close to the 
root of the knowledge tree you build on a particular subject, pruning the 
bad branches can sometimes cause the whole tree to collapse.
  -- Mike Duffy in cljs, <news:Xns9FB6521286DB8invalidcom@94.75.214.39>

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Good use of bitwise NOT "~" or unnecessary obfuscation? RobG <rgqld@iinet.net.au> - 2012-11-01 18:32 -0700
  Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Denis McMahon <denismfmcmahon@gmail.com> - 2012-11-02 06:14 +0000
    Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-02 02:28 -0700
  Re: Good use of bitwise NOT "~" or unnecessary obfuscation? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-02 10:22 +0100
    Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-02 10:37 +0100
    Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-02 06:25 -0700
      Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Asen Bozhilov <asen.bozhilov@gmail.com> - 2012-11-02 06:35 -0700
      Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-11-02 14:58 +0100
        Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-02 08:49 -0700
          Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-11-04 21:52 +0100
            Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-04 22:49 +0000
              Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-11-05 13:18 +0100
              Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-06 06:48 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-06 15:04 +0000
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Gene Wirchenko <genew@ocis.net> - 2012-11-06 10:43 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-06 11:22 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-06 12:16 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-06 12:53 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-11-07 17:34 +0100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-07 23:21 +0100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-07 23:23 +0100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Gene Wirchenko <genew@ocis.net> - 2012-11-07 17:00 -0800
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 07:16 +0100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Dr J R Stockton <reply1245@merlyn.demon.co.uk.invalid> - 2012-11-07 17:50 +0000
            Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Dr J R Stockton <reply1245@merlyn.demon.co.uk.invalid> - 2012-11-05 19:26 +0000
              Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Stefan Weiss <krewecherl@gmail.com> - 2012-11-07 22:13 +0100
        Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Gene Wirchenko <genew@ocis.net> - 2012-11-02 09:51 -0700
      Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-02 18:41 +0100
        Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-02 12:30 -0700
          Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-02 20:33 +0000
            Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-11-04 21:57 +0100
              Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-04 22:44 +0000
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Andrew Poulos <ap_prog@hotmail.com> - 2012-11-05 15:41 +1100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Tim Streater <timstreater@greenbee.net> - 2012-11-05 09:07 +0000
          Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-02 22:10 +0100
            Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-02 15:22 -0700
              Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-03 10:19 +0100
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Patricia Shanahan <pats@acm.org> - 2012-11-03 13:05 -0700
                Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-03 21:39 +0100
        Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-03 12:26 +0100
  Re: Good use of bitwise NOT "~" or unnecessary obfuscation? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-11-02 12:28 +0200
    Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Gene Wirchenko <genew@ocis.net> - 2012-11-02 10:00 -0700
  Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Asen Bozhilov <asen.bozhilov@gmail.com> - 2012-11-02 06:15 -0700
  Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-06 06:32 -0800
    Re: Good use of bitwise NOT "~" or unnecessary obfuscation? RobG <rgqld@iinet.net.au> - 2012-11-06 18:23 -0800
      Re: Good use of bitwise NOT "~" or unnecessary obfuscation? Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-07 11:22 -0800

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