Subject: Dr. Westall's debug services

(This message is being sent to CPSC 215 Students and TA's)

(prescript: Don't forget the midterm is Wed 19 OCT)

This message is intended to clarify any misconceptions
regarding the scope of my debugging services, it is being
sent because I received a couple of "nastygrams" from one
student who expressed concerns that my methods were unfair.

I don't really think my methods differ in substance from
those of other faculty,  but just to ensure everybody is
aware of what they are I provide this description:

Specifically, the student asserted:

> I don't think it's fair for you to tell me that my program is working
> and then fail to tell me that you didn't check it with images that
> you would be likely to test it on, then wait for me to find out about
> that after the due date. I understand that it is only one point, and
> that I have the rest of the day to fix it, but it's not a matter of
> points anymore. It's a matter of principle. I find that this is
> completely unfair.

This assertion seems to based upon the following two messages that
I DID SEND to the student along with a copy of the a2t1.txt on
which I tested.

>> OK, this last one is MUCH better! It compiles
>> without warning, the DBG output looks correct,
>> and so does the a2t1.txt image."

and later:

>> I'm not sure why you can't make an
>> image with a2t1.txt.  I ran it this
>> way and a2t1.ppm seemed to be correct
>> to me. I guess you could have a platform
>> dependent bug.

Those messages were intended to tell the student that his/her
program did indeed APPEAR to render the mustard yellow back wall
correctly on the machine on which I tested. Having programmed
for 40 years I am extremely careful NEVER to state that any
program is CORRECT (as in: WILL NOT FAIL ON ANY INPUT). I fully
expect that over half of the programs that receive 100 COULD BE
BROKEN with more extensive testing.

The student went on to imply that I KNEW his/her program
was broken but deliberately withheld said info.

> I'm just hurt at the fact
> that I asked you a question, and
> you almost practically did refrain from
> telling me the complete truth.

This on hurt MY feelings! I have been BUSTING MY TAIL trying
to do the best I can to find/solve your problems. And when I
find a bug, all but one of you know I'm NOT SHY when it comes to
telling you about it. I have been in the business of teaching
programming for 30 years now and I would NEVER EVER WITHHOLD
KNOWLEDGE of errors in a student program for ANY REASON!!!

The student also  seemed to assume that I would test
his/her program using all possible inputs or
at least all inputs that would be used in evaluating
the program before commenting on its correctness.

I regret  if somehow I conveyed that expectation
to that student or anyone else. I definitely didn't
mean to do that.

--------------------------------------

Here are the proper expectations regarding debug help.

1 - If include an input file, provide its name in
    your e-mail and request that I test on that file,
    I will do so and report the results of testing
    ON THAT FILE.

2 - If you wish for me to test on ONE specific machine
    on which I have a login ID, I will do that IF
    YOU SEND ME THE MACHINE NAME.

3 - If you send me a tar ball and no input file
    or don't identify a specific input file,
    I will test on a single "minimal standard"
    input file that I use for ALL students.

4 - Under NO circumstances do I "guarantee" that
    I can find all the bugs in your submission
    (or my OWN PROGRAMS) for that matter.

5 - I DO NOT promise to pre-test your programs on all
    inputs that will be used in evaluating them.
    In the "real world" they don't do that either.

6 - If I tell you that your program appeared to work
    correctly on input blah.txt, it does NOT MEAN
    that your program is CORRECT! A correct program
    works correctly on all possible inputs.  Basically
    it is IMPOSSIBLE to prove in ANY rational way
    that a program of this size is correct.

mw