Distributed: Friday, May 11, 2007
Due: noon, Friday, May 18, 2007
No extensions.
This page may be found online at http://www.cs.grinnell.edu/~rebelsky/Courses/CS302/2007S//Exams/final.html.
This exam is also available in PDF format.
Contents
There are four problems on the exam. Some problems have subproblems.
Each problem is worth the same number of points. The point value
associated with a problem does not necessarily correspond to the
complexity of the problem or the time required to solve the problem.
Experience shows that different people find different problems
complex. Hence, if you get stuck on an early problem, try moving
on to another problem and let your subconscious work on the early
problem. (You'll also get a better sense of accomplishment if you
can find at least one problem that you can solve early.)
This examination is open book, open notes, open mind, open computer,
open Web. However, it is closed person. That means you should not
talk to other people about the exam. Other than as restricted by that
limitation, you should feel free to use all reasonable resources available
to you. As always, you are expected to turn in your own work. If you
find ideas in a book or on the Web, be sure to cite them appropriately.
Although you may use the Web for this exam, you may not post your answers
to this examination on the Web (at least not until after I return exams
to you). And, in case it's not clear, you may not ask others (in person,
via email, via IM, by posting a please help
message, or in any
other way) to put answers on the Web.
This is a take-home examination. You may use any time or times you deem
appropriate to complete the exam, provided you return it to me by the
due date.
I expect that someone who has mastered the material and works at
a moderate rate should have little trouble completing the exam in a
reasonable amount of time. In particular, this exam is likely to take
you about eight hours, depending on how well you've learned topics
and how fast you work. You should not work more than twelve hours
on this exam. Stop at twelve hours and write There's more to life
than CS
and you will earn at least 70 points on this exam.
I would also appreciate it if you would write down the amount of time
each problem takes. Each person who does so will earn two points of
extra credit. Since I worry about the amount of time my exams take,
I will give two points of extra credit to the first two people who
honestly report that they've spent at least six hours on the exam or
completed the exam. (At that point, I may then change the exam.)
You must include both of the following statements on the cover sheet of the
examination. Please sign and date each statement. Note that the
statements must be true; if you are unable to sign either statement,
please talk to me at your earliest convenience. You need not reveal
the particulars of the dishonesty, simply that it happened. Note also that
inappropriate assistance
is assistance from (or to) anyone
other than Professor Rebelsky (that's me) or Professor Davis.
1. I have neither received nor given inappropriate assistance on this
examination.
2. I am not aware of any other students who have given
or received inappropriate assistance on this examination.
Because different students may be taking the exam at different times,
you are not permitted to discuss the exam with anyone until after I
have returned it. If you must say something about the exam, you are
allowed to say This is among the hardest exams I have ever taken.
If you don't start it early, you will have no chance of finishing the
exam.
You may also summarize these policies. You may not tell
other students which problems you've finished. You may not tell other
students how long you've spent on the exam.
You must present your exam to me in two forms: both physically and
electronically. That is, you must write all of your answers using the
computer, print them out, number the pages, put your name on the top
of every page, and hand me the printed copy. You must also email me
a copy of your exam. You should create the emailed version by copying
the various parts of your exam and pasting them into an email message.
In both cases, you should put your answers in the same order as the
problems. Failure to name and number the printed pages will lead to a
penalty of two points. Failure to turn in both versions may lead to
a much worse penalty.
In many problems, I ask you to write code. Unless I specify otherwise
in a problem, you should write working code and include examples that
show that you've tested the code.
Just as you should be careful and precise when you write code and
documentation, so should you be careful and precise when you write prose.
Please check your spelling and grammar. Since I should be equally
careful, the whole class will receive one point of extra credit for each
error in spelling or grammar you identify on this exam. I will limit
that form of extra credit to five points.
I will give partial credit for partially correct answers. You ensure
the best possible grade for yourself by emphasizing your answer and
including a clear set of work that you used to derive the
answer.
I may not be available at the time you take the exam. If you feel that
a question is badly worded or impossible to answer, note the problem you
have observed and attempt to reword the question in such a way that it
is answerable. If it's a reasonable hour (before 10 p.m. and after 8
a.m.), feel free to try to call me in the office (269-4410) or at home
(236-7445).
I will also reserve time at the start of classes next week
to discuss any general questions you have on the exam.
Topics: The Big Picture
, Primary literature
As you know, one important focus of this course is to help you develop
the skills to read the literature
, that is, the papers in
journals and conferences that provide the central ideas of computer
science in general and programming languages in specific. I help you
develop those skills by having you read and respond to a wide variety
of papers.
Each semester, I update my list of papers to use in the course. For
this question, you have the opportunity to affect that choice.
a. Find a paper from the research literature that would be
appropriate to include in CSC302. When I say research literature
,
I mean that you should focus on articles from journals and conferences,
rather than on Web pages or on manuals and such. Obtain a copy of that
paper for yourself and make a copy for me. (You should submit my copy
along with the exam.) If you need help getting a paper whose title you
have found, feel free to ask me for help.
b. In a paragraph or two, describe the state of the field of programming
languages at the time the paper was written.
c. Summarize the thesis of the paper.
d. In two or three paragraphs, explain how including this paper in
the CSC302 syllabus would benefit the course.
Topics: Introspection, Java, Ruby
One technique we explored this semester was introspection (closely
related to reflection), in which we can write programs that can
take apart classes and objects to look at the internal issues.
In four or so paragraphs, explain the similarities and differences between
the implementation of introspection in Java and the implementation of
introspection in Ruby. Make sure to use sample code in your explanations.
Topics: Types, Polymorphism, Java, Scheme, C
In On Understanding Types, Data Abstraction, and Polymorphism
, Cardelli
and Wegner identify four kinds of polymorphism, two universal (parametric and
inclusion) and two ad hoc (overloading and coercion).
a. Which of these four kinds of polymorphism does Scheme support? For each
kind that Scheme supports, provide an illustrative example.
b. Which of these four kinds of polymorphism does Java support? For each
kind that Java supports, provide an illustrative example.
c. Which of these four kinds of polymorphism does C support? For each
kind that C supports, provide an illustrative example.
Topics: Garbage Collection, Prolog, PostScript, Scripting Languages
An accompanying diagram provides a simple
illustration of a state of memory during the execution of a program. In this
diagram, each grey square represents one cell of memory. The small number in
the lower-left-hand-corner of each cell is that cell's memory location. The
larger number in each cell is the contents of that cell. For the purposes
of this problem, you should assume that each cell contains a pointer. The
darker squares and rectangles represent objects.
For example, a length-two object resides in cells 26 and 27, and contains
pointers to the length-three object in cells 10-12 and the length-one
object in cell 30.
In this problem, you will explore the effect of garbage collecting this
memory using each of three algorithms. For each collection, you can assume
that the root set contains only the address 25. (You may also use the
address 15, which appeared in an earlier verison of the exam. Amazingly,
the two addresses give the same live set.)
i. Draw the state of memory after a mark-and-sweep collector cleans up.
You may find it useful to use this diagram
of empty memory.
Although mark-and-sweep collectors do not clear
cells, you should leave any cells that are available blank.
ii. Draw the state of memory after a mark-and-compact collector cleans up.
You may find it useful to use this diagram
of empty memory.
Although mark-and-compact collectors do not clear
cells, you should leave any cells that are available blank.
iii. Draw the state of memory after a simple semispace collector cleans
up. You may find it useful to use
this diagram of a separate space in memory.
Although semispace collectors do not clear cells, you should leave any cells
that are available blank.
The following remove_first predicate is used to determine
whether a list can be created by removing one value from another list.
In particular, remove_first(X,Lst,NewLst) holds if
NewLst is the same as Lst, but with the first
instance of X removed.
remove_first(X,[],[]).
remove_first(X,[X|Xs],Ys) :- equal_lists(Xs,Ys).
remove_first(X,[Y|Ys],[Y|Zs]) :- neq(X,Y),remove_first(X,Ys,Zs).
equal_lists([],[]).
equal_lists([X|Xs], [X|Ys]) :- equal_lists(Xs,Ys).
neq(a,b). neq(a,c). neq(a,d).
neq(b,a). neq(b,c). neq(b,d).
neq(c,a). neq(c,b). neq(c,d).
neq(d,a). neq(d,b). neq(d,c).
For example,
| ?- remove_first(a,[a,b,c],[b,c]).
true ?
yes
| ?- remove_first(b,[a,b,c],[a,c]).
true ?
yes
| ?- remove_first(c,[a,b,c],[a,b]).
true ?
yes
| ?- remove_first(d,[a,b,c],[a,b,c]).
true ?
yes
| ?- remove_first(a,[a,b,c],[a,b,c]).
no
| ?- remove_first(a,[a,b,a,c],[b,a,c]).
true ?
yes
| ?- remove_first(a,[a,b,a,c],[b,a,c]).
true ?
yes
| ?- remove_first(a,[a,b,a,c],[a,b,c]).
no
i. Explain why we use the neq predicate in the third
portion of the definition of remove_first.
ii. Explain what happens when you provide a variable for the third parameter
of remove_first. For example, why do you get the results
you get when you ask for remove_first(a, [a,b,a,c], X)?
iii. Explain what happens when you provide a variable for the second parameter
of remove_first.
iv. Explain what happens when you provide variables for the first and third
parameters of remove_first.
I've written a PostScript procedure, linebetween, that draws
a line between the two points on the top of the stack. For example, if
we have 10 20 100 200 on the stack and then call linebetween,
PostScript will draw a line between the points (10,20) and (100,200).
The linebetween procedure also removes the four values from
the stack.
Here's a simple PostScript program to draw a house using linebetween.
You can see it in action by saving it in a file with a .ps suffix
and then opening the file with ghostview, which is available through the
gv command.
%!PS-Adobe-3.0
%%BoundingBox: 0 0 612 792
%%LanguageLevel: 1
%%EndComments
0.0 0.0 0.0 setrgbcolor
10 setlinewidth
/linebetween { moveto lineto stroke } def
100 100 200 100 linebetween
100 100 100 180 linebetween
200 100 200 180 linebetween
75 155 150 230 linebetween
225 155 150 230 linebetween
showpage
%%EOF
Write and test a PostScript procedure, rectangle that draws
a rectangle, assuming the
stack contains the x coordinate of the left, the y coordinate of the
bottom, the width, and the height of the rectangle.
For example, the following should draw a rectangle with corners of
(100,200), (150,200), (150,300), and (100,300).
In writing rectangle, you may use only
linebetween and the following PostScript stack manipulation
procedures: add, dup, exch,
index, pop, and roll.
Your procedure should not leave any values on the stack.
i. In two or three paragraphs,
argue that Scheme is a scripting language,
using Ousterhout's discussion of scripting languages as your primary
basis.
ii. In two or three paragraphs,
argue that Scheme is not a scripting language,
using Ousterhout's discussion of scripting languages as your primary
basis.
Cardelli, Luca & Wegner, Peter. (1985). On Understanding Types, Data Abstraction, and Polymorphism. ACM Computing Surveys 17(4), December 1985.
Ousterhout, John K. (March 1988). Scripting: Higher-level programming for the 21st century. IEEE Computer 31(3), pp. 23-30.
These are some of the questions students have asked about the
exam and my answers to those questions.
Problem 1
Problem 2
Problem 3
Problem 4
Here you will find errors of spelling, grammar, and design that
students have noted. Remember, each error found corresponds to a
point of extra credit for everyone. I usually limit such extra credit to
five points. However, if I make an astoundingly large number of errors,
then I will provide more extra credit.
- Spurious "at the implementation" in problem 2. [EO'N, 1 point]
- In problem 2, "you explantations" should be "your explanations".
[EB, 1 point]
- "Paragraph of two" should be "Paragraph or two".
[MU/DD, 1 point]
- "the the" appears at least once (or did, before the error was caught).
[JW/EO'N, 1 point]
- PDF link goes to midsem. [JT, 1 point]
-
ghostview is gv in the MathLAN. [JT, 1 point]
- When changing the addresses in the illustration, Sam forgot to change the
root address in the code. That root address should be 25, rather than 15.
[EO, 1 point]
Thursday, 10 May 2007 [Samuel A. Rebelsky]
- Designed exam.
- Wrote exam.
Friday, 11 May 2007 [Samuel A. Rebelsky]
;
Check with Bobby