sub filter($f, @arr) {
    my @out;
    
    for @arr -> $e {
        if $f($e) {
            @out.push($e)
        }
    }
    
    @out;
}

my @even = filter { $_ mod 2 == 0 }, 1..10;
@even ~~ (2, 4, 6, 8, 10) or die "Wrong array {@even}";