Homework 6

This homework covers material in Chapter 3 of Essentials of Programming Languages (EOPL).

This homework is due in the bin in CST 3-212 by noon on Friday, March 7.

You may work singly or in pairs on this assignment.

EXERCISES

For this assignment, you'll need a copy of the file interp-3-5.scm which is the interpreter discussed in class.

(25 points) EOPL, Exercises 3.11, 3.12, and 3.17 (no need to answer the testing question).
Note that the 3.7 portion (mentioned in 3.12 and 3.17) is really from Lab 6, but you'll need them to adequately test your answers.
(15 points) EOPL, Exercise 3.13.
(15 points) EOPL, Exercise 3.18.
As an example of its usage, the following code should evaluate to 68, because 5 + 7 9 = 68:
```
unpack a b c d = cons(5,cdr(list(6,7,8,9))) 
 in +(a,*(b,d))
```
In contrast, the following code should result in an error:
```
unpack a b c d = cons(5,cdr(list(6,7,8,9,10))) 
 in +(a,*(b,d))
```
(15 points) EOPL, Exercise 3.20.
(20 points) EOPL, Exercise 3.29.
At a minimum, the entry message should include both the formal and actual parameters, and the exit message should include the result. As an example, the result of evaluating
```
let tester = traceproc (x,y) *(v,+(x,y)) 
 in (tester 3 4)
```
should look something like the following:
```
--> let tester = traceproc (x,y) *(v,+(x,y)) in (tester 3 4)
entering procedure with parameters: x=3 y=4
leaving procedure, with result: 35
35
-->
```
Note that the second 35 is the value of the entire expression.

A few hints/suggestions:

To state the obvious, unpack is a variation of let. First, understand what is going on with let, then understand what is different about unpack, and then, and only then, think about coding things.
For the traceproc problem, add a new record structure to the procval datatype for this new sort of procedure.
Also for the traceproc problem, your messages do not need to be sophisticated or pretty. As a very simple procedure to write both a message and a Scheme value, you can use the following (or design your own):
```
(define myprint
   (lambda (str obj)
      (begin
        (display str)
        (display obj))))
```
You may find Scheme's begin construct (see Dybvig, Section 5.2) useful to sequence a series of expressions, as in myprint above.