ch12.102_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 12 of "Perl Best Practices"   ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;

Readonly my $EXPR  => qr{foo}xms;
Readonly my $VAR   => qr{bar}xms;
Readonly my $LIST  => qr{1[.][.]9}xms;
Readonly my $BLOCK => qr{ [{] [.]{3} [}] }xms;


Readonly my $WITH_BLOCK => qr{
   with \s+                                 # Always a 'with' keyword
   (?: each \s+                             #  If followed by 'each'
       (?:$EXPR                             #    Then expect an expression
         | $VAR  \s* in \s* [(] $LIST [)]   #    or a variable and list
       )
     | [(] $LIST [)]                        #  Otherwise, no 'each' and just a list
   )
   \s* $BLOCK                               # And the loop block always at the end
}xms;

croak 'oops!'    if 'with er go est' =~ $WITH_BLOCK;
croak 'matched!' if 'with each bar in (1..9) {...}' =~ $WITH_BLOCK;