import (
  qaqao:collections:Collection,
  qaqao:cursors:Forward-Cursor
),
// Cells are included in the standard environment

implementation (

  One-way-linked-component-Type [Meta-Type (
    supertypes « (Collection-Type),
    instance « (
      supertypes « (One-way-linked-component (Item-type « Item-type,
                                              Structure-type « instance)),
      attributes « (Item-type Type,
                    Structure-type One-way-linked-component-Type)
    )],

  [One-way-linked-component (
    Item-type Type,
    Structure-type One-way-linked-component-Type
  )] [One-way-linked-component-Type (
    supertypes « (Bounded-Collection (Item-type « Item-type)),
    instance « (
      representation « (
        item  [Cell (Item-type « Item-type)],
        next  [Cell (Item-type « Structure-type)],
        state [Cell (Item-type « Component-state)]
      ),
      receives « (
        empty? (replies [state = Component-state.EMPTY]),
        size?  (replies « [if [state = Component-state.EMPTY]
                           then 0
                           else [1 + [next ← size]]]),
        get-Cursor
          (replies « [[Component-Cursor (Item-type « Item-type,
                                         Structure-type « Structure-type)]
                       ← make-cursor])
      )
    ),
    receives « (
      make-empty-component (
        does « {
          component « memory ←
            [allocate (item  « [[Cell (Item-type « Item-type)] ← make-cell],
                       next  « [[Cell (Item-type « Structure-type)] ← make-cell],
                       state « [[Cell (Item-type « Component-state)] ← make-cell]
            )];
          component:state ← [set-item (item « Component-state:EMPTY)]
        },
        replies « component
      )
      [make-filled-component (item Item-type, structure Structure-type)] (
        does « {
          component « [memory ←
            [allocate (item  « [[Cell (Item-type « Item-type)] ← make-cell],
                       next  « [[Cell (Item-type « Structure-type)] ← make-cell],
                       state « [[Cell (Item-type « Component-state)] ← make-cell]
            )]];
          ( component:item  ← [set-item (item « item)],
            component:next  ← [set-item (item « structure)],
            component:state ← [set-item (item « Component-state:NOT_EMPTY)]
          )
        },
        replies « component
      )
    )
  )],

  Component-state [Enumerated-Type (
    supertypes « (Equality-Type),
    members « (EMPTY, NOT_EMPTY)
    // *** Do we need to implement/override = ?
    // *** Or do such enumeration types handle this automatically?
    // *** If so, how?
  )],

  [Component-Cursor (
    Item-type      Type,
    Structure-type One-way-linked-component-Type
  )] [Type (
    supertypes « (Forward-Cursor (Item-type « Item-type)),
    instance « (
      representation « (
        component [Cell (Item-type « [One-way-linked-component (
                                        Item-type « Item-type,
                                        Structure-type « Structure-type
                                      )])]
      ),
      receives « (
        at-item? (replies « [¬ [component ← is-empty?]]),
        get-item (replies « [[component ← get-item]:item]),
        move-to-next (
          does « {
            component ← [set-item (item « [[component ← get-item]:next])]
          }
        )
      )
    ),
    receives « (
      [make-cursor (component [One-way-linked-component (
                                 Item-type « Item-type,
                                 Structure-type « Structure-type
                               )])] (
        replies « [memory ← [allocate (
          component « [Cell (Item-type « [One-way-linked-component (
                                           Item-type « Item-type,
                                           Structure-type « Structure-type
                                          )])] ← make-cell]]
        )
      )
    )
  )]

)
      

/* This type and meta-type are abstract classes; that is, they have no
   public interface. They are therefore only usable in implementations
   of other classes. */