use warnings;
use strict;

my @colors = qw/ red white blue /;
my $rotate = cycle( 2, \@colors );

for ( 1..10 ) {
	print &$rotate . "\n";
}

sub cycle {
    my ( $toggle, $items ) = @_;
    my $error = '';
    if ( $toggle !~ /^\d+$/ or $toggle == 0 ) {
        $error = "The first argument to &alternate must be a positive integer: $toggle\n";
    }
    if ( ! @$items ) {
        $error .= "The second argument to &alternate must be an array reference.";
    }
    die $error if $error;
    my $count = 0;
    my $index = -1;
    return sub {
        $index += 1 if $count++ % $toggle == 0;
        $index = 0  if $index == @$items;
        $items->[ $index ];
    }
}