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January 25, 2013
[Issue 9390] New: Option for verbose regular expressions
http://d.puremagic.com/issues/show_bug.cgi?id=9390

          Summary: Option for verbose regular expressions
          Product: D
          Version: D2
         Platform: All
       OS/Version: All
           Status: NEW
         Severity: enhancement
         Priority: P2
        Component: Phobos
       AssignedTo: nobody@puremagic.com
       ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2013-01-24 18:14:01 PST ---
I'd really like an option to write "verbose" regular expressions in D, like in
Python:

http://docs.python.org/2/library/re.html


> re.X
> re.VERBOSE
> 
>     This flag allows you to write regular expressions that look
>     nicer. Whitespace within the pattern is ignored, except when in a
>     character class or preceded by an unescaped backslash, and, when
>     a line contains a '#' neither in a character class or preceded by
>     an unescaped backslash, all characters from the leftmost such '#'
>     through the end of the line are ignored.
> 
>     That means that the two following regular expression objects that
>     match a decimal number are functionally equal:
> 
>     a = re.compile(r"""\d +  # the integral part
>                        \.    # the decimal point
>                        \d *  # some fractional digits""", re.X)
>     b = re.compile(r"\d+\.\d*")


RE code is code like every other, so it enjoys comments, a nicer indenting and
formatting.

Making RE more readable helps their debug and understand. In my Python code all
RE longer than half a line of chars are "verbose".

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January 25, 2013
[Issue 9390] Option for verbose regular expressions
http://d.puremagic.com/issues/show_bug.cgi?id=9390


Dmitry Olshansky <dmitry.olsh@gmail.com> changed:

          What    |Removed                     |Added
----------------------------------------------------------------------------
                CC|                            |dmitry.olsh@gmail.com


--- Comment #1 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2013-01-25 12:13:45 PST ---
How about adding the common extensions that is called comments inside regular
expression.

I can't recall synatx off-hand but it's something like:
(?# some comment that is ignored)


Plus you can already use any of the follwoing:

auto pattern - r"the first piece" // comment
r"the second piece" //comment 2
...
r" the last piece"; //last comment


Or if implicit concatenation feels too dirty:

auto pattern - r"the first piece"  // comment
~ r"the second piece" //comment 2
...
~ r" the last piece"; //last comment

Either way free-form regex + top-level explanatory note is enough by my
standards. The rationale is if you have to explan every piece in isolation then
it's one of 2 cases: you are explaning machanics to people that don't know what
regex is (and it's wrong) or the regex pattern is too darn complex for its own
good.

Since this is enhancement request I hereby propose 2 ways to solve it: close as
won't fix or add the aformentioned extension for comments (that at least is
more or less common). I'm not going to add another option that messes with
syntax rules.

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