my class IO::File is Cool does IO::FileTestable {
    has Str $.file;
    has Str $.dir = '.';

    multi method Str(IO::File:D:) {
        self.file;
    }
    multi method gist(IO::File:D:) {
        "IO::File<$.path>";
    }
    multi method Numeric(IO::File:D:) {
        self.file.Numeric;
    }
    multi method Bridge(IO::File:D:) {
        self.file.Bridge;
    }
    multi method Int(IO::File:D:) {
        self.file.Int;
    }

    method path(IO::File:D:) {
        $.dir eq '.' ?? $.file !! join('/', $.dir, $.file);
    }

    method open(IO::File:D: *%opts) {
        open($.path, |%opts);
    }
}


sub dir(Cool $path = '.', Mu :$test = none('.', '..')) {
    my Mu $RSA := pir::new__PS('OS').readdir(nqp::unbox_s($path.Str));
    my int $elems = pir::set__IP($RSA);
    my @res;
    loop (my int $i = 0; $i < $elems; $i = $i + 1) {
        my Str $file := nqp::p6box_s(nqp::atpos($RSA, $i));
        @res.push: IO::File.new(:$file, :dir($path)) if $test.ACCEPTS($file);
    }
    return @res;

    CATCH {
        default {
            X::IO::Dir.new(
                :$path,
                os-error => .Str,
            ).throw;
        }
    }
}

for dir() {
    .say if .f && /<+[A..Z]>/;
}