test.pl

use v6;

module MyApp {

    class Foo {
        has $.name;
        has $.things = [];
        method add_thing (Foo $thing) {
            $.things.push($thing);
        }
    }

    my $*dyn;
    sub foo (Foo $thing, Callable $body) is export {
        if $*dyn {
            $*dyn.add_thing($thing);
        }
        $*dyn = $thing;
        $body.();
        return $thing;
    }
}

import MyApp;

my $foo = foo MyApp::Foo.new(name => 'a'), {
    foo MyApp::Foo.new(name => 'b'), sub {
    };
    foo MyApp::Foo.new(name => 'c'), {
        foo MyApp::Foo.new(name => 'd'), sub {
        };
    };
};

say $foo.perl