#!/usr/bin/perl
use strict;
use warnings;

my ($stellen,@elemente)=@ARGV;
die "Aufruf:\n   $0 stellen element_a [element_b [element_c [ ...]]]\n" if(@elemente==0 || $stellen!~/^\d+$/);

sub permutation($@)
{
  my ($st,@arr) = @_;
  my @ret=();
  my @cnt=map{$_=0}(1..$st);
  ende:while(1)
  {
   push(@ret,join('',map{$_=$arr[$_]}@{[@cnt]}));
   for my $i (0..$st-1)
   {
    if($cnt[$i]<@arr-1)
    {
     $cnt[$i]++;
     last;
    }
    else
    {
     $cnt[$i]=0;
     last(ende) unless( exists($cnt[$i+1]) );
    }
   }
  }
  return @ret;
}

print "Elemente: ".join('; ', @elemente)."\n";
print "Stellen: $stellen\n";
print "Variantionen:\n";
print join("\n",&permutation($stellen,@elemente)),"\n";

sub mkPerms {
  my($n, @arr) = @_;

  return($n ? map { my $item = $_; map { $item . $_ } mkPerms($n-1, @arr) } @arr : "");
}

print $_ . "\n" for ( mkPerms(3, 'A'..'C') );

sub mkPerms {
  my($n, $arr) = @_;

  return($n ? map { my $item=$_; map { $item . $_ } mkPerms($n-1, $arr) } @$arr : "");
}

print $_ . "\n" for ( mkPerms(3, [ 'A'..'C' ]) );

#!/usr/bin/perl

use strict;
use warnings;

package Wheel;

sub new {
    my $class = shift;
    my @items = @_;
    my $self = {
        items       => \@items,
        position    => 0,
        notch       => [],
    };
    bless $self, $class;
    return $self;
}

sub on_notch {
    my $self = shift;
    my $call = shift || sub { print "Notch!\n" };
    push @{$self->{notch}}, $call;
}

sub succ {
    my $self = shift;
    if ($self->{position}++ < $#{$self->{items}}) {
        $self->{position} and return $self->{items}->[$self->{position}];
    } else {
        $self->{position} = 0;
        $_->() for @{$self->{notch}};
        return $self->{items}->[$self->{position}];
    }
    
}

sub to_s {
    my $self = shift;
    return $self->{items}->[$self->{position}];
}

package Odometer;
use Data::Dumper;

my $DONE = 0;

sub new {
    my $class = shift;
    my $self = [];
    return bless $self, $class;
}

sub add_wheel {
    my $self = shift;
    my @items = @_;
    my $w = Wheel->new(@items);
    push @$self, $w;
    $self->[$#$self-1]->on_notch(sub {$w->succ}) if $#$self > 0;
}

sub succ {
    my $self = shift;
    my $temp = $self->to_s;
    $self->[0]->succ;
    
    if ($DONE == 2) {
        return undef;
    } else {
        $DONE++ if $DONE;
        return $temp;
    }
}

sub to_s {
    my $self = shift;
    return join ' ', map { $_->to_s } reverse @$self;
}

sub add_termination {
    my $self = shift;
    $self->[-1]->on_notch( sub { $DONE = 1} );
}

package main;

my $o = Odometer->new;
#$o->add_wheel(qw/red green blue yellow/);
$o->add_wheel(1, 3, 5) for (1..3);
#$o->add_wheel(2, 4);
$o->add_termination;
while (my $cur = $o->succ) {
    print $cur . "\n";
};