Homework 09: Symbolic Evaluation of Boolean Expressions in Java

Due: Wednesday 10am Friday, March 2526, 20092010

Overview

Write a Java program boolSimp.dj1 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:

• the symbols T and F denoting the boolean values true and false ;
• boolean variables (represented by symbols other than T, F, !,
  &, |, >, and ?=) that can be bound to either =true
  or false .
• the unary function ! meaning not .
• the binary functions &, |, and > meanding
  denoting and, or, and implies, respectively), and
• the ternary function ? meaning if .

The shorter names T, F, !, &, |, >, and ? are used instead of
true, false, not, and, or, implies, and ={{if=}) for notational brevity which matters in very large nputsinputs.

The course staff is providing:

• a Scheme program in the file boolsimp.ss equivalent to the Java program that you are required to write;
• a Java "stub" file boolSimp.dj1 that defines a composite hierarchy
  of "abstract syntax" tree classes rooted in the class Form representing boolean
  expresssions;
• 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 (commented out) simplify() method that composes the visitors you must write in boolSimp.dj1 to simplify whatever formula the Parser instance contains.
• a Java "stub" test file boolSimpTest.java that includes some rudimentary tests of the code in the boolSimp.dj1 stub file.

...

If you omit the new File(...) construction in the argument to Parser and use "<}} fileName {{><fileName>" instead,
you will create a Parser for the String "< fileName >{}" <fileName>". which is interpreted
as a simple boolean variable.
The File input format is important because it enables us to
conveniently teat apply your simplifier on 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.dj1. 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.dj1 and boolSimpTest.java, simply submit expanded
versions of these files
via OwlNet 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 .dj1 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. Please remember to save you file boolSimpTest.java as a .java file not as a .dj1
file.

Correction: we now recommend using Advanced Level ( .dj2=) files instead of Full Java ( .java {{) files in mixed compilation with Intermediate Level files. You should be able to consistently use }} .dj2 {{ files instead of }} .java= files if you download the latest version of DrJava from www.cs.rice.edu/~javaplt/drjavarice. See the Addendum below.

The Scheme file boolsimp.ss includes Scheme functions parse and
unparse to translate Scheme lists into abstract syntax trees and
vice-versa. Scheme provides a simple external syntax for lists (in
homage to is LISP heritage) but Java does not. Hence the java
Parser class works on Java strings instead of lists. The Java visitor class
Print in the BoolSimp.java file performs unparsing of the abstract syntax
types Form
and IfForm to type String.

The Scheme parsing functions rely on the following Scheme data definitions.

...

• a boolean constant true and false ;
• a symbol S representing a boolean variable;
• (make-Not X) where X is a boolExp ;
• (make-And X Y) where =X and Y are =boolExp=s boolExps;
• (make-Or X Y) where =X and Y are =boolExp=s boolExps;
• (make-Implies X Y) where ={{X and Y are =boolExp=s boolExps; or
• (make-If X Y Z) where X, Y, and Z are =boolExp=s boolExps.

Note: The or operator must be written a as | in Scheme instead of
| because | is a metasymbol with a special meaning in Scheme (akin
to ='=).

...