Computer Science 136 Data Structures and Advanced Programming Williams College Fall 2005

Short Answers

Complete the following problems from the book and turn them in as a text file lab7.txt at the start of lab.

Lab Program

This week's laboratory is described in Section 9.5 in the Bailey book.

Before lab, copy the starter files from the cs136 shared area under labs/postscript on the Macs or FreeBSD systems. Familiarize yourself with these three classes and make sure you understand how they work.

Come to lab with a handwritten sketch of the Interpreter class that you will be writing (where you will process the tokens being delivered to your interpreter by the provided iterator class).

A few things to consider as you implement this lab:

• Please name the file with your interpreter Interpreter.java.
• Make use of the functionality of the classes you are given to start. Be careful not to spend time developing code that is already there!
• Make your main method very short. All it should do is create an Interpreter object and tell it to start parsing the postscript program presented at the command line. Create a method interpret that takes a single parameter of type java.util.Iterator<Token> (which will be an instance of the provided Reader class) and processes the PostScript tokens returned by that Iterator<Token>.
• Develop your interpret method incrementally. Get your simple push, pop, and pstack operations working, then move on to the arithmetic operators, and finally the definition and usage of symbols.
• Your program should throw exceptions when it encounters invalid input, but these should contain meaningful error messages. You can use Assert.condition() and Assert.fail() for this.
• Answer thought questions 1, 2, and 5.
• For an extra point, you can implement procedures as described in thought question 3. If you design everything else properly, this should be almost a trivial extension.
• For another extra point, you can implement the if operator as described in thought question 4.

When you're finished, create and submit a tar file lab7.tar that includes the following:

• Your well-documented source code for Interpreter.java. Indicate clearly in the comment at the top of your program if you have implemented the extensions in thought questions 3 and 4.
• A README file that contains your answers to thought questions 1, 2, and 5.

You should not include the three files from the textbook's web page in your submitted tar file.