How do I do parametered roles?

[Austin Hastings]

Suppose that I have, for example:

  class Session {
    has @:messages;

    method clear_messages() {...}
    method add_message($msg) {...}
    method have_messages() {...}
    method get_messages() returns Array {... font color="black" ...}
  }

And suppose I add to it:

  class Session {
    has @:messages;

    method clear_messages() {...}
    method add_message($msg) {...}
    method have_messages() {...}
    method get_messages() returns Array {... font color="black" ...}

    has @:errors;

    method clear_errors() {...}
    method add_error($msg) {...}
    method have_errors() {...}
    method get_errors() returns Array {... font color="red" ...}
  }

So I realize that not only is the whole list-of-messages thing a packageable
behavior (read: Role or Class) but that this particular behavior recurs
within my class.

One solution is to compose member objects that implement this behavior:

  if ($my_object.messages.have_messages) {...}

But that sucks.

What I want to do is to say:

1- There's a "list of generic messages" role.
2- The ListOfMessages defines an attribute.
3- The ListOfMessages needs some sort of customizable behavior.

And then implement two different parameterized invocations of the same role
(MetaRole?)

  class Session
  {
    does ListOfMessages
         (
           attribute_base => 'messages',
           method_base    => 'messages',
           display_color  => 'black'
         );

    does ListOfMessages
         (
           attribute_base => 'errors',
           method_base    => 'errors',
           display_color  => 'red'
         );

    ...
  }

(Classes are described as "parameterless subroutines". I'd like a
parameterful one.)

Can I just do:

  role ListOfMessages($attribute_base, $method_base, $display_color) {...}

or what?

=Austin