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

my $iter = combo( 30..50 );
while ( my @combo = $iter->() ) {
    print "@combo\n";
}

sub combo {
    my @list = @_;
    return sub { () } if ! @_;

    my (@position, @stop, $end_pos, $done);
    my ($by, $next) = (0, 1);

    return sub {
        return () if $done;
        if ( $next ) {
            $by++;
            return () if $by > @list;
            @position = (0 .. $by - 2, $by - 2);
            @stop     = @list - $by .. $#list;
            $end_pos  = $#position;
            $next = undef;
        }
        my $cur = $end_pos;
        {
            if ( ++$position[ $cur ] > $stop[ $cur ] ) {
                $position[ --$cur ]++;
                redo if $position[ $cur ] > $stop[ $cur ];
                my $new_pos = $position[ $cur ];
                @position[ $cur .. $end_pos ] = $new_pos .. $new_pos + $by;
            }
        }
        if ( $position[0] == $stop[0] ) {
            $position[0] == @list ? $done = 1 : $next = 1;
        }
        return @list[ @position ];
    }
}