import (
  objects « (qaqao:cursors:Forward-Cursor)
);
// Boolean and Integer+ are included in the standard environment

interface (declarations « (

  Collection-Type [Meta-Type (
    instance « (
      instance « (
        attributes « (
          Item-type Type
        ),
        receives « (
          empty?     (replies Boolean),
          get-Cursor (replies [Forward-Cursor (Item-type « Item-type)])
        )
      )
    )
  )],

  [Collection (Item-type Type)] Collection-Type,
  
  [Bounded-Collection (Item-type Type)] [Collection-Type (
    supertypes « (
      Bounded-Collection (Item-type [Supertype-Type (type « Item-type)]),
      Collection (Item-type [Supertype-Type (type « Item-type)])
    ),
    instance « (
      receives « (
        empty? (replies Boolean « [[instance ← size?] = 0]),
        size?  (replies Integer+)
      )
    )
  )]

))

/* Collection and Bounded-Collection are abstract types;
 * that is, there are no direct implmentations
 * of these types. Subtypes may also be abstract.
 */