Exercise 8.3
Representing HTML with objects in Scheme ****

This is an open exercise - maybe the start of a minor project.

In the original mirror of HTML in Scheme, the HTML mirror functions, return strings. In the current version, the mirror functions return an internal syntax tree representation of the web documents. With this, it is realistic to validate a document against a grammar while it is constructed. In this exercise we will experiment with an object representation of a web document. We will use the class and object representation which we have introduced in this lecture.

Construct a general class html-element which implement the general properties of a HTML element object. These include:

1. A method that generates a rendering of the element
2. A method that returns the list of constituents
3. An abstract method that performs context free validation of the element

In addition, construct one or more examples of specific subclasses of html-element , such as html , head , or body. These subclasses should have methods to access particular, required constituents of an element instance, such as the head and the body of a HTML element, and title of a head element. Also, the concrete validation predicate must be redefined for each specific element.