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Regex: a little Clojure DSL for readable, compositional regexes (github.com)
4 points by henning 2493 days ago | hide | past | web | 3 comments | favorite



Looks good.

Regex have long been tarnished with the bad readability stain. But that shouldn't always be the case, for eg. the Clojure example:

    (def datestamp-re
      (let [d {\0 \9}]
        (regex [d d d d :as :year] \- [d d :as :month] \- [d d :as :day])))
Could be written in Perl like so:

    sub datestamp_re {
        qr/ (?<year> \d \d \d \d) - (?<month> \d \d) - (?<day> \d \d ) /x;
    }
Perl has had named captures since 2007. The captures are stored %+ variable (ie. $+{year}, $+{month} & $+{date}).

The /x (on the end of the regex object qr) allows whitespace & newlines in the regex composition making it much easier to read. Anyone doing a longer than a few chars regex should always have this :)

And composing your regex in bites is definitely a good idea:

    sub datestamp_re  {
        my $year = qr/(?<year>\d{4})/;  # defined with named capture
        my $dom  = qr/\d{2}/;           # day or month (2 digit)
    
        qr/ $year - (?<month>$dom) - (?<day>$dom) /x;
    }

    sub re_match {
        my ($re, $text) = @_;
        if ($text =~ $re) { return { %+ } }
        return;
    }

    re.pl> re_match datestamp_re, '2007-10-23';
      {
        day => 23,
        month => 10,
        year => 2007
      }

    re.pl> re_match datestamp_re, '20X7-10-23';
    
    re.pl>


The main issue I see with this Clojure library at the moment is the lack of tests. Other than the general idea is worthwhile and not hard to explore in most functional languages.


Something like Perl6 Rules / Grammar maybe a good target to explore: http://en.wikipedia.org/wiki/Perl_6_rules




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