Could be worse :)

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1189605

use strict;
use warnings;
$| = 1;

sub err { die "ERROR: ", s/\G/<@_>/r, "\n" }

sub crossmap               # this is clear, isn't it?
  {
  my ($left, $right) = @_;
  [ map { my $prefix = $_ ; map $prefix.$_, @$right } @$left ];
  }

sub expr
  {
  my $answer = [ '' ];

  while( /\G (
      \|        (?{ 'ALTERNATION'    })
    | \d+       (?{ 'STRING'         })
    | \[ \d+ \] (?{ 'CHARACTERCLASS' })
    | \(        (?{ 'PARENTHESIS'    })
    ) /gcx )
    {
    goto $^R;

  ALTERNATION:
    $answer = [ @$answer, @{ expr() } ];
    next;

  STRING:
    $answer = crossmap $answer, [ $1 ];
    next;

  CHARACTERCLASS:
    $answer = crossmap $answer, [ $1 =~ /\d/g ];
    next;

  PARENTHESIS:
    $answer = crossmap $answer, expr();
    /\G\)/gc or err "missing ')'";
    }

  return $answer;
  }

while(<DATA>)
  {
  chomp;
  print "$_ => ";
  my $answer = expr();
  /\G\z/gc or err "incomplete parse";
  local $" = ',';
  print "@$answer\n";
  }

__DATA__
(65|70)
(3[678]|4[1678])
5[45]
(6[4569]|7[01])
[download]

> Could be worse :)

agreed! ;)

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}

You shouldn't be despaired, the demonstrated code is neither easy to read nor maintain.

Depends on who's reading it, and who's maintaining it. If so.

Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you post live.

originally from ...

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}