Why can't Regular Expressions use keywords instead of characters?

Question

Okay, I barely understand RegEx basics, but why couldn\'t they design it to use keywords (like SQL) instead of some cryptic wildcard characters and symbols?

Is it for pe

Answer 1

Perl 6 is taking a pretty revolutionary step forward in regex readability. Consider an address of the form: 100 E Main St Springfield MA 01234

Here's a moderately-readable Perl 5 compatible regex to parse that (many corner cases not handled):

 m/
     ([1-9]\d*)\s+
     ((?:N|S|E|W)\s+)?
     (\w+(?:\s+\w+)*)\s+
     (ave|ln|st|rd)\s+
     ([:alpha:]+(?:\s+[:alpha:]+)*)\s+
     ([A-Z]{2})\s+
     (\d{5}(?:-\d{4})?)
  /ix;

This Perl 6 regex has the same behavior:

grammar USMailAddress {
     rule  TOP {     }

     rule  addr { <[1..9]>\d* ?
                    }
     token direction { N | S | E | W }
     token streetname { \w+ [ \s+ \w+ ]* }
     token streettype {:i ave | ln | rd | st }
     token city {  [ \s+  ]* }
     token state { <[A..Z]>**{2} }
     token zip { \d**{5} [ - \d**{4} ]? }
  }

A Perl 6 grammar is a class, and the tokens are all invokable methods. Use it like this:

if $addr ~~ m/^$/ {
     say "$, $";
}

This example comes from a talk I presented at the Frozen Perl 2009 workshop. The Rakudo implementation of Perl 6 is complete enough that this example works today.