method Supply()
    {
        supply
        {
            sub subscribe
            {
                say "building a supply for $.root: files = " ~ @.files;
                my $events = Supply.merge( @.files.map( { .watch } ) );
                $events.merge( %.subdirs.values.map( { .Supply } ) );

                my $watch = supply {
                    whenever $events      { emit ( False, $_ ) };
                    whenever $.root.watch { emit ( True, $_ ); done };
                };

                whenever $watch
                {
                    .say;
                    if ( .[0] )
                    {
                        self.scan(); subscribe;
                    }
                    .[1].emit;
                }
            }
            subscribe;
        }
    }