CS 341 - Principles of Programming Languages
Homework #8

Due: at the beginning of class 15

Note: This work is to be done in pairs. Each pair will submit one assignment. Although you may divide the work, both team members should be able to present/describe their partner's work upon request.

To submit this homework, change into the directory containing all necessary files: MiniScheme3.jj and supporting abstract syntax tree .java files, and enter the command "submit341 ms3".

MiniScheme Project Phase 3

In this phase of the project, you will extend phase 2 to include Boolean values and operators, if-else, relational operators, and type predicates: #t, #f, and, or, not, if, eqv? (for integer and boolean), <, integer?, boolean?

Notes:

We will continue to restrict "read" and "write" to handle only integer input and output for simplicity. As a result, most testing will use "if" to select integer output for the testing of your phase 3 operators. Accordingly, be sure that, after creating a class to represent your Booleans, you should next turn attention to correct interpretation of "if" before anything else.
In Scheme, anything that is not #f is treated as a true value, so your Boolean operators will not have errors with non-Boolean types. (Read R5RS section 6.3.1 on Booleans carefully.) You are encouraged to try to get type error messages with the and, or, and not operators. You will not experience them, and will gain insight into the correct working of the Boolean operators (defined in sections 4.2.1 and 6.3.1).
Read 6.1 to better understand the correct behavior of the equivalence predicate eqv?. In our implementation, two no-value expressions (e.g. "(write 1)" and "(write 2)") are considered eqv? equal.
The less than operator (<) should given the same messages and same error code as arithmetic operators when given operand(s) that are not integers.

Grammar

Grammar notes:

Non-terminals are surrounded with angle brackets "<" and ">".
Terminals (e.g. "(" and ")" are represented as themselves without quotes, unless otherwise noted below).
--> denotes a right arrow. Choices to the right of the arrow are separated by a pipe (i.e. "|").
{ }* and { }+ denote a Kleene star and plus/cross, respectively. { }? denotes an optional subexpression.

<program> --> { <definition> | <expression> }*

<definition> --> ( define <variable> <expression> )

<variable> --> <any <identifier> that isn't also a keyword>
<identifier> --> <initial> { <subsequent> }*
<initial> --> [a-z!$%&*/:<=>?^_~]
<subsequent> --> <initial> | <digit> | [+-.@]
<digit> --> [0-9]

<expression> --> <variable>
| <literal>
| <conditional>
| <assignment>
| <derived expression>

<literal> --> <integer> | <boolean>
<integer> --> { + | - }? { <digit> }+
<boolean> --> #t | #f

<conditional> --> ( if <expression> <expression> { <expression> }? )

<assignment> --> ( set! <variable> <expression> )

<derived expression> --> ( read )
| ( write <expression> )
| ( newline )
| ( + <expression> <expression> )
| ( - <expression> <expression> )
| ( * <expression> <expression> )
| ( quotient <expression> <expression> )
| ( let ( { <binding spec> }* ) <body> )
| ( and { <expression> }* )
| ( or { <expression> }* )
| ( not <expression> )
| ( eqv? <expression> <expression> )
| ( < <expression> <expression> )
| ( integer? <expression> )
| ( boolean? <expression> )

<binding spec> --> ( <variable> <expression> )

<body> --> { <definition> }* { <expression> }+