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

my @array = 0 .. 30;

my $interval = make_interval();
for my $val ( @array ) {
    &$interval( 4);
    $val = "--";
};

local $, = " ";
print @array, $/;

sub make_interval {
    my $ctr = 0;
    my $start = 1;
    return sub {
        if ( $start) { $start = 0; return }
        $ctr++;
        if ( $ctr == $_[0]) { $ctr = 0 } else { no warnings; next }
    }
}