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Homework 09: Symbolic Evaluation of Boolean Expressions in Java

Due: 10am

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Monday,

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April 4,

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2011

Overview

Write a Java program boolSimp.dj1dj that reduces boolean expressions (represented in the input and output streams in Scheme-like notation) to simplified form. For the purposes of this assignment, boolean expressions are Scheme expressions constructed from:

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  • a Scheme program in the file boolsimp.ss equivalent to the Java program that you are required to write;
  • a Java "stub" file boolSimp.dj1dj that defines a composite hierarchy of "abstract syntax" tree classes rooted in the class Form representing boolean expressions;
  • a Java library file Parser.java contain a class Parser with
    • a read() method that reads a boolean expression represented in "Scheme form" and returns the corresponsing Java Form abstract syntax tree and
    • a reduce() method that composes the visitors you must write in boolSimp.dj1dj to reduce whatever formula the Parser instance contains to simplified form.
  • a Java "stub" test file boolSimpTest.java that includes some rudimentary tests of the code in the boolSimp.dj1dj stub file.

The stub file BoolSimp.dj1dj also includes comments showing you exactly what code you have to write to complete writing your simplifier. Of course, you also need to write corresponding tests and add them to the file BoolSimpTest.java.

The file Parser.java is provided to enable you to test your solution on large inputs stored in files. Parser.java includes two Parser constructors Parser(File file) and Parser(String form) for building parsers to parse the boolean expression (in external text form) in the specified File or String, respectively. Since the library class File is defined in the package java.io, you need to insert either

Code Block

import java.io.*;

or more specifically

Code Block

import java.io.File;

at the head of a test file that uses the Parser class on the contents of a file.
To construct a Parser for the formula in a file {{}} <fileName> you must invoke

Code Block
new Parser(new File("<fileName>"));

If you omit the new File(...) construction in the argument to Parser and use "<fileName>" instead, you will create a Parser for the String "<fileName>". which is interpreted as a simple boolean variable. The File input format is important because it enables us to conveniently apply your simplifier to formulas that are thousands of symbols long. As a result, you only have to translate the Scheme code in boolsimp.ss into corresponding cleanly-written OO Java code by filling in the gaps in our Java stub file boolSimp.dj1dj. You are expected to appropriately use the composite, interpreter, singleton, and visitor patterns in the code that you write. Since the only stub files that you have to modify are boolSimp.dj1dj and boolSimpTest.java, simply submit expanded versions of these files via OwlSpace to submit your assignment. Warning: we will run your program on large inputs to determine if you wrote the code correctly. Try using the large test files provided on the course wiki.

We have formatted the test files as a .java file rather than a .dj1dj because the Language Levels facility peforms no useful augmentation of JUnit test classes and bypassing the language levels translator avoids some annoying bugs in the implementation of that facility. When using the "Save As" command, please remember to save you file boolSimpTest.java as a .java file not as a .dj1dj file. The "Save" command always retains the file types of all files.

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The Java abstract syntax classes include a separate composite hierarchy (called IfForm) for representing boolean expression as conditionals (the type ifExp in boolsimp.ss). This representation includes only three concrete variant classes, making it much easier to write the visitors that perform normalization, evaluation, and clean-up.

The visitor pattern is a straightforward but notationally involved alternative to the interpreter pattern.. You can mechanically translate interpreter pattern code to visitor pattern code. (Perhaps IDEs like Eclipse should support such transformations.) The interpreter solution to this assignment is easier to write than the visitor solution described in the preceding program description. If you are still learning Java mechanics, you are encouraged to write an interpreter solution first and translate it (if you can) to visitor form. A perfect interpreter solution will only be penalized 15% versus a perfect visitor solution. If you submit an interpreter solution, your program must conform to class signatures given in the interpreter pattern support code below (just as a visitor solution must conform to the class signatures given in the visitor pattern code below).

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Here are the links for the files:

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The following files contain large formulas that can be reduced by your simplifier. Only the file files named bigData x require a larger thread stack size than the JVM default on my laptop. I used the most platforms. NOTE: to handle the bigData x files, you must set JVM argument -Xss64M for the Interactions JVM to get the bigData files to runJVM using the DrJava Preferences command on the Edit menu. The JVM argument setting can be found on the last panel (called JVMs) in the Preferences categories tree.