Implementing Dependents and Dependencies in Lisp: Tasks

Protocol for dependents of objects

Define generic functions map-dependents, add-dependent and delete-dependent.

Define a class to represent objects with dependents, called dependent-mixin. Note that the actual dependents should be stored in a slot called dependents for which you should provide a reader function called dependents-of.
Define a generic function make-collection-for-dependent-mixin.
Define a make-collection-for-dependent-mixin method for dependent-mixins which creates and returns an instance of a simple-childed-mixin (from the collection protocol).
Define an after method for initialize-instance on dependent-mixin which calls make-collection-for-dependent-mixin and stores the result in the dependents slot of the dependent-mixin object.

Define a class called dependency-mixin. Note that the actual dependencies should be stored in a slot called dependencies for which you should provide a reader function called dependenciess-of.
Define make-collection-for-dependency-mixin and a suitable after method for initialize-instance, following the same pattern as when you defined the dependent-mixin class.

Define methods for map-dependents, add-dependent and delete-dependent which specialize on dependent-mixin. Use functions such as add-child to implement the functionality required.
Define methods for map-dependencies, add-dependency and delete-dependent which specialize on dependency-mixin.
Now glue them together by defining after methods on add-dependent, add-dependency, delete-dependent and delete-dependency. For example, define an after method for add-dependent which calls add-dependency.

Check that your implementation works! In particular make sure your functions adhere to the protocols.