#!/usr/bin/perl

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

use strict;
use warnings;
$| = 1;

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

sub crossmap
  {
  my ($left, $right) = @_;
  [ map { my $prefix = $_ ; map $prefix.$_, @$right } @$left ];
  }

sub expr
  {
  my $answer = [ '' ];
  
  print("\ndebug ", s/\G/<<you are here with [@$answer]>>/r, " end  " ),
  $answer = /\G\|/gc      ? [ @$answer, @{ expr() } ] :
    /\G\d+/gc     ? crossmap $answer, [ $& ] :
    /\G\[\d+\]/gc ? crossmap $answer, [ $& =~ /\d/g ] :
    /\G\(/gc      ? ( crossmap($answer, expr()),
                    /\G\)/gc || err "missing ')'")[0] :
    return $answer while 1;
  }

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])