CIS 352   —   SPRING 2009

Homework 7 (Draft)

Coverage

• Essentials of Programming Languages (EOPL): Section 4.3.

Logistics

• You may work singly or in pairs on this assignment.

• Be sure you mark (via comments) each change you make to the interpreter files.
  (See the Homework Policy for more details.)

What to Turn in:

• A copy of the source code of each file modified.

• DO NOT turn in the source code from files you did not modify.

• A run of your code that verifies that it passes all the tests in your test harness.

How to turn in your work:

1. If you have more than one file to submit, bundle them into a zip or tar archive.

2. Click on this electronic-submission link, and use your NetID and password for authorization.
   Important: Make sure you select CIS 352 as the course for which you're submitting.

PROBLEMS

Do only one of the following options. If you choose option B, we will offer advice, but no hand holding.

Option A

1. (30 points)   EOPL Exercise 4.17

2. (35 points)   EOPL Exercise 4.19

3. (35 points)   EOPL Exercise 4.21

Option B (only for the brave and self confident)

1. (120 points)   EOPL Exercise 4.22
   Part of the point of this problem is for you to make a design decisions on your own. In particular, the authors leave it up to you what goes into the expression language. At the very least, you must have the problem's four examples working.

Notes

• Remember that map is your friend and extend-env* is a good thing to have.

• For Exercise 4.19:

  • First understand what is going on in Exercise 4.16.
  • Now consider the even/odd example of Figure 4.7. What your modified interpreter would do on this letrec would be equivalent to:

      let even = 0 
          odd  = 0
       in begin
            set even = proc(dummy) ...;
            set odd  = proc(dummy) ...;
            the body of the letrec
          end
    

  • So, extend-env-rec* cesses being a data-structure (i.e., you remove it from the environment data-type) and turns it into a regular function that builds the proper environment to evaluate the body of the letrec.
  • Note: Be careful using the instrument-let tracing, you now have circular structures!

• For Exercise 4.21:

  • Where do you store the old value of the variable?
    How about a fresh location in the store.
    Or better yet, be lazy (like I was) and save it in local variable in value-of.

• For Exercise 4.22:

  • You are pretty much on your own on this one.