Functional Problem Solving (CSC 151 2016S) : Handouts

Notes on Homework

These notes on homework were written toward the end of Fall 2013.

Because of the breakdown in grading this semester, we have not caught a number of issues with your code that would have been caught earlier. In general, I haven not taken off for these issues when grading. But they are things you should certainly pay attention to as you work on your projects and exams.


At this point in the semester, you should be comfortable writing documentation for procedures. And your default should be to write the full six-P style documentation for procedures. (You'll note that we do so for almost every procedure we provide.) At minimum, you should write the first four P's.

If you copy code from an assignment, you should be copying the documentation, too.

It's also worthwhile to include documentation beyond the six P's.

Finally, every assignment should start with an introductory comment. Something like the following:

#lang racket
(require gigls/unsafe)

; Lea R. Ner and Stu Dent
; CSC 151.02 2013F
; Assignment 8: Trees
; Tuesday, 12 November 2013

; Citations:
;   We took tree-depth, tree-size, image-render-color-tree!, and
;     ctree->image from the reading.
;   We took tree-flatten from lab ....
;   Alex G and Chike A helped us with problem 3 by suggesting that we
;     find the middle of the two indices.
;   AHD and JOP helped us debug problem 4.

The introductory comments will definitely matter on the project. And future classes will expect something similar.


Many of you seem a bit confused as to what kind of conditional to use in various situations. Here are the guidelines I usually use. You don't need to follow them strictly (in fact, you can't follow them strictly), but you should think about

  • If you have more than one consequent (typically, if you want to do more than one operation with side effects), you probably need a cond expression or a when expression.
  • If you plan to do a sequence of tests that should only go as far as the first test that holds, use a cond expression.
  • If you have only one test, use an if expression or a when expression.
  • If you have an alternate, use if or cond. If you have no alternate, use when (or, sometimes, cond.


Please take care to reformat your code. It should be easy: You can just use Ctrl-I. You can also select a chunk of text and hit Tab.

Please watch too-long lines. Ideally, no line should be greater than 80 columns. Sensible line breaks also make your code much more readable.

It's a lot easier for the grader if you clearly indicate when each answer starts. Something like the following would be good.

; ----------------------------------------------------------------------
; Problem 1 - List-Like Color Trees

For if statements, I really like the test to be on the same line as the if and the consequent and alternates on lines by themselves (unless everything fits on one line).

(if test

In contast, I almost always like the conditions for cond on separate lines. (If the tests and consequents are relatively small, they can be on the same line.)



Please carbon copy your partners when you submit work. It makes it easier for me to return comments to everyone in your group.

For assignment 8, almost no one filled out the epilogue. I expect that's a consequence of the grading problems. But the epilogue is really more for you than it is for us - it's an opportunity for you to reflect on learning and problems from the assignment.

Please provide examples of your procedures in action (either working or failing to work). You can copy and paste from the interactions pane, and then copy out the lines.

You might also find it useful to include unit tests. (Remember that lab on unit testing that we did right before fall break? No, probably not, as it was right before fall break.)

A few of you showed the steps you went through and added some comments on your thought processes. Doing so is very helpful if you show me your work on a problem - failed attempts, how you know they failed, what the failure made you think about, etc. In some cases, I gave full credit on a problem with really good documentation of thought processes.

In trying to figure out what's going wrong, it can be very useful to show what you expect the output to be, and then run the procedure “by hand” to see what's happening. (Sometimes using display in your code can also give you some info.)

Don't forget to use let when you are doing identical computations. (And when you are doing nearly-identical computations, see if you can make them both slight variants of identical computations.)