Add a class Function to define evaluable functions to this model. A reasonable approach would be for the class Function to define a default evaluation method that returns the function as a pattern to...

Add a class Function to define evaluable functions to this model. A reasonable approach would be for the class Function to define a default evaluation method that returns the function as a pattern to be unified. Subclasses of Function can perform actual evaluations of interest. Test your implementation using functions such as simple arithmetic operations, or an equals method that returns true or false.