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

Followups directed to: comp.lang.javascript

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[I had written a longer reply with examples, but apparently it has not 
reached Usenet.  So I will keep this one shorter and expand on it upon 
request.]

Patricia Shanahan wrote:

> On 11/2/2012 2:10 PM, Thomas 'PointedEars' Lahn wrote:
>> Patricia Shanahan wrote:
>>> On 11/2/2012 10:41 AM, Thomas 'PointedEars' Lahn wrote:
>>>> Patricia Shanahan wrote:
>>>>> On 11/2/2012 2:22 AM, Evertjan. wrote:
>>>>> ...
>>>>>> if ( /foo/.test(someString) ) {..}
>>>>>>
>>>>>> I trust not understanding Regex is not a valid counterargument.
>>>>> If I'm prepared to look at it long enough, I can generally work out
>>>>> what a Regex does, but Regex does not seem to me to be a very
>>>>> human-friendly, smoothly readable language.
>>>> That depends on the flavor and your experience with them.
>>> Well, I don't quite have 30 years of experience with regular expressions
>>> yet, but it's getting close.
>> Which flavors?
> 
> Assorted UNIX shell tools (lex, grep, egrep, vi, ed, sed, awk etc.),
> Perl, PHP, and Java.

As I see it, implementations of regular expressions are lacking readability 
because of two factors: insufficient expressiveness and stringly typing.

Insufficient expressiveness or excessive verbosity means you have to write 
longer expressions for rather simply concepts.  Consider, for example, POSIX 
`[[:space:]]' vs. Perl/PCRE `\s'.  Consider POSIX Basic Regular Expressions 
(BRE) `\{0,1\}' vs. POSIX Extended Regular Expressions (ERE)'s and 
Perl's/Perl-Compatible Regular Expressions (PCRE)'s `?'.  Consider POSIX BRE 
`\{1,\}' vs. ERE's/Perl's/PCRE's `+'.

Stringly typing, i. e. expressing data in string literals instead of in 
regular expression literals, causes regular expressions to be less readable, 
and in turn code that uses regular expressions to be less readable, due to 
the fact that string literals have their own escaping mechanism.  

I have not done much lex.  But as you probably know, POSIX grep, vi(m), ed, 
sed, awk & friends only support POSIX Basic Regular Expressions.  BRE both 
lack expressiveness and are stringly typed in direct use.  So they cannot be 
shining examples of readable regular expressions.

ERE as supported by POSIX egrep and GNU grep improve on that slightly by 
reversing expression logic (so you have to escape what you do *not* want to 
be special instead), by adding shortcuts for `{0,1}' and `{1,}' and 
alternation.  But they still have the excessive verbosity and stringly 
typing problem of POSIX REs.

Perl RE and PCRE (the latter is supported by GNU grep) improve on 
readability again by providing regular expression literals with and, among 
other powerful features such as interpolation, flags to improve readability 
specifically (such as `/x').  But you have to be aware of that.

While PHP eventually supports PCRE and allows a wider range of delimiters, 
its RE implementation suffers from the fact that there are no regular 
expression literals.  It steps back to stringly typing.  So does Java, but 
Java essentially allows only one delimiter and no multi-line syntax; another 
two steps back.  Java's RE implementation, in addition to that, suffers from 
Java's static typing and the excessive verbosity in implementation that 
brings.  So both of them do not provide good examples either.

You have not mentioned Python.  Python's implementation is a step back from 
PHP and Java in that it does not support PCRE, but its own PCRE-inspired 
flavor.  However, it is a step forward from that because of Python's 
implicit string concatenation, raw-strings to alleviate the escaping 
problem, and new RE features.

By comparison, ECMAScript and its implementations have regular expression 
literals, but those have no variable delimiter, no interpolation, no multi-
line syntax, and they do not support PCRE but their own flavor yet again.  
But on the plus side the languages are dynamic enough so that you can work 
around those shortcomings (as I did in JSX:regexp.js).

(There are also other RE implementations, like that of Microsoft, which 
primarily suffer from the fact that they are very different to the common 
aforementioned ones, or have limited use.  If you ever tried to use RE to 
search with Visual Studio, you know what I mean.)

Finally, as a third factor to readability of code using regular expressions, 
here comes in the person responsible for writing it.  Many people use 
regular expressions where they are not strictly necessary.  And they write 
needlessly complicated regular expressions because they do not know better 
or do not care.  Specifically for ECMAScript implementations (but you can 
also find similar bloat code elsewhere), people escape `/' in *string* 
literals passed to the RegExp constructor because `/' is the delimiter of 
*RegExp* literals.  They needlessly escape special characters in character 
classes.  They use alternation where character classes would have sufficed.  
And so on.

Attempting to avoid regular expressions where they are not necessary, and 
simplifying regular expressions where they are, thereby improving 
readability, goes a long way towards understanding them, and vice-versa.  
You can find examples of that in many of my follow-ups in comp.lang.ALL and 
de.comp.lang.ALL.


PointedEars
-- 
When all you know is jQuery, every problem looks $(olvable).

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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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