Com S 342 --- Principles of Programming Languages

		     EXERCISE 10: REFERENCES
                 (File $Date: 2005/03/28 07:07:37 $)

The purpose of this exercise is for you to learn about how references
are used in the interpreter of section 3.7.

As with all exercises, this is to be done individually.  And it is due
the day this topic is planned to be discussed in class, unless
specified otherwise (see the syllabus at:
http://www.cs.iastate.edu/~cs342/syllabus.shtml).

We expect this to help you think about the readings (see below).
If you don't have an answer or an answer that you think is good,
write down what you read, and a question or two that would have helped
you make progress.   Then you can ask that question in class;
there will be other people with the same problem, and everyone can
learn by discussing these issues.  And you'll most likely see similar
things on the homework, so it's best to understand them now.

READINGS: Read section 3.7 of "Essentials of Programming
Languages" (2nd ed., 2001) by Friedman, Wand, and Haynes.

1. [Understanding references]

a. Why are references implemented using a position and a vector in
   Scheme?

b. If you were working in C++, how would you implement references?

c. In section 3.7, what's the difference between deref and
   primitive-deref?

d. How does apply-env-ref create a reference?

e. Why are references needed to implement assignment in the
   interpreter of section 3.7?

WHAT TO HAND IN

You should have at the beginning of class,  your answers
to the above questions (or questions and problems you encountered for
each part).  Make sure your name is on these. Attach the printouts, if
any, requested above.