class MatchContext {
    has $.name;
    has $.available is rw;
}

class Option {
    has $.name;
    has $.supply is rw;

    method callback() {
        $!supply.tap(
            -> $v {
                given $v {
                    if .available {
                        if .name eq $!name {
                            .available = False;
                        }
                    }
                }
            }
        );
    }
}

sub getopt(@args is copy = @*ARGS) {
    my $p = Supplier.new;
    my @options = [
        Option.new(name => "a", supply => $p.Supply),
        Option.new(name => "b", supply => $p.Supply),
    ];

    @options[0].callback();
    @options[1].callback();

    sub parse(Supply $source --> Supply) {
        supply {
            whenever $source {
                if .starts-with('-') || .starts-with('--') {
                    note "In Parser: Emit the option {.Str}";
                    $p.emit(
                        my $mc = MatchContext.new(
                            name => .substr(1),
                            :available
                    ));
                    emit "The {.Str} matched ? " ~ ($mc.available ?? 'FAILED' !! 'OK');
                }
            }
        }
    }

    my $parse = parse(Supply.from-list(@args));

    react {
        whenever $parse -> $msg {
            say "In MAIN: GOT MESSAGE: ", $msg;
        }
    }

    note "done the supplier";
    $p.done;
}

&getopt();