This project is extending the language “PASTA” (which was deveoped in c) to be an object-oriented language. It adds additional language features, which enable users to define classes, methods as well as create instances. While developing this project, I have used instructions of a suggested assignment from the book “Structure and Interpretation of Computer Programs”, which can be found in here: https://mitpress.mit.edu/sicp/psets/ps7oop/readme.html Please refer to file 'README.pdf' for more detailed instructions.

A ‘define-class’ special expression takes in the name of the class, a list of superclass which the class inherits from, and zero or more names for slots (the instance variables). Every class has to have at least one super class. There is a predefined class ‘object’, and any other class is its subclass. Classes are stored in the top level of the environment. As a result of that, name of each class has to be unique. A class can have multiple superclasses. Instances belong to a class can be applied methods that belong to that class’s superclasses. When defining a new class, its superclass’s slots will also be carried over.

A ‘define-method’ special expression takes in the name of the method, name of the class that this method can be applied to, and an lambda-exp. Names of methods are stored the same as names of classes, so their have to be unique, and classes and methods could not share the same name either. You could not define a method that could be applied to an non-existing class. The lambda-exp can take in extra arguments, just like our normal lambda expression. Note that lambda expression has to have ‘self’ as the first parameter.

Users can create instances by the ‘make’ expression. The expression takes name of a class, and then slots’ names and values pairs.

When applying a method to an instance, we need to use the ‘tell’ expression. It takes the instance’s name, name of the method, and zero or more extra arguments.

Set expression needs to take three arguments. It takes the name of the instance, name of the slot, and the new value you want to assign to the slot. This expression will always return the updated instance value.

Since methods and classes are all stored together in the top level. Methods could not have same names, even if they are for different classes. I think it will be more intuitive if the interpreter could handle methods with the same name but belong to different class. In addition to that, in the current version, subclasses can not override methods from their superclasses. It will be great if the language have both ‘override’ and ‘overload’(methods that have same name, but take in different parameters) functions.