CSC 160
Homework 2

Assigned 6 Feb, due 16 Feb

Note change of due date on account of weather!

Problems

• Exercise 3.1.3 (defining a six-copies variable)
• One of Exercises 4.4.2 through 4.4.5
• Exercise 4.6.2 (box diagram)
• Exercise 5.2.4 (defining a surround function). Note: This exercise is in chapter 5, before the Design Recipe had been introduced, so you're not strictly required to use the recipe. But it's still a good idea!
• Exercise 5.2.6: identify parameters and arguments in your solution to 5.2.4
• Exercise 5.5.3: draw a box diagram for your solution to 5.2.4
• Exercise 6.3.3: pinwheel contract
• Exercise 6.3.5: bullseye contract
• Exercise 6.4.3: pinwheel examples
• Exercise 6.4.4: checkerboard2 examples
• Exercise 6.4.5: bullseye examples
• Exercise 6.5.3: pinwheel skeleton
• Exercise 6.5.4: checkerboard2 skeleton
• Exercise 6.5.5: bullseye skeleton
• Exercise 6.6.2: pinwheel definition
• Exercise 6.6.3: checkerboard2 definition
• Exercise 6.7.1: pinwheel and checkerboard2 testing
• Design a checkerboard4 function that takes in two color names (like checkerboard2) and produces a 4x4 checkerboard in those colors. Follow all the steps of the design recipe, in order. Hint: this will be short and simple if you re-use previously-defined functions!
• 

  Extra credit: The version of pinwheel that I originally wrote works nicely for square pictures, but not so well for pictures that are longer than they are high, or vice versa; see the picture at right.

  
  

  Develop a function smart-pinwheel that fits things together snugly, as in the picture at right. Hint: You can do this with image-beside-align-top, image-beside-align-bottom, image-above-align-left, and/or image-above-align-right. Another approach is to look in the "Help Desk" documentation for "image.ss"; look in particular for the word "pinhole", which is how the teachpack lines up one picture with another.

What to turn in and how

For problems 4.6.2 (a box diagram), 5.2.6 (identifying parameters and arguments), and 5.5.3 (another box diagram), I recommend printing out the relevant Scheme code on paper, drawing on the paper, and turning in the paper. (This can be done on the computer, but I think it's more hassle than it's worth.)

For the bullseye function, I asked you to write a contract, examples, and skeleton, but no body (because I haven't yet told you everything you need to write the body). Write these exactly as if you were going to write a body and test it, but realize that it won't pass a syntax check or run. To turn it in, comment out each line of the skeleton and examples, and include it in the same Definitions window with the rest (see below).
The same goes for any function that for which you don't finish a working body; do the contract, examples, and skeleton anyway, comment this stuff out, and include it in the same Definitions window with the rest.

For the remaining problems, I recommend using the "Log Definitions and Interactions" command on the "File" menu:

1. Write the various expressions, function contracts, examples, and function definitions in the Definitions Window.
2. Click "Run". You should see the results of your examples, along with what they "should be", in the Interactions window.
3. Choose "Log Definitions and Interactions" from the File menu. It will ask you for a "log directory"; I recommend creating a directory named something like "CSC 160 HW2" and using this.
4. Choose "Stop Logging" from the File menu.
5. Just to make sure it worked, choose "Open" from the File menu and look in the directory you chose before. You should see two files: 01-definitions and 01-interactions. The definitions file is probably identical to your definitions window. 01-interactions should be whatever was in the Interactions window before you clicked "Log Definitions and Interactions", i.e. just after you clicked "Run".
   (If you see more than two files, e.g. 02-definitions and 02-interactions, it means you clicked "Run" after you started logging. No harm done; the 01 files represent what things looked like before you started logging, and the 02 files represent what things looked like after you hit "Run". Examine all the files and decide which ones to send me.)
6. Send me an e-mail, attaching both files 01-definitions and 01-interactions. If you've put all the problems into one Definitions window, you should only need to send these two files; if you've done each problem in a separate window, you'll need to send a lot of files, with a good chance of one of them getting lost.) Make sure to put your name in the Subject line!

Alternatively, you can click "Run" and then save the Definitions and Interactions windows to two separate files, and send me both of these files.

Also turn in a log of how many errors of different kinds you encountered in the assignment, with brief comments describing each one ("mismatched parentheses" is self-explanatory, but more complex errors might need more description). Note that "errors" means not only error messages from DrScheme, but also wrong answers.

General advice

For all assignments in chapters 6 and later, be sure to follow the design recipe. (And it couldn't hurt for problem 5.2.4 either, but it's not required.)

Be sure to choose meaningful names for functions and parameters, and watch for opportunities to re-use functions you (or the textbook) have already written.

This assignment is to be done in pairs, using the ideas from the "kindergarten" article. Choose a partner ASAP and schedule time to work together on the assignment. When you're finished, turn in one assignment with both names on it. You'll have a different partner for homework 3, so if you don't get along with this partner, remember it's only for a week.

Grading standards

Error log:       /25
(I'm not grading on how many or how few errors you encountered, only on whether you recorded them correctly.)

Exercise 3.1.3:    /10
Exercise 4.4.2-4.4.5:    /20
Exercise 4.6.2:    /10
Exercise 5.2.4:    /20
Exercise 5.2.6:    /10
Exercise 5.5.3:    /10

The table below has columns for each step in the design recipe. You won't turn in a separate skeleton and definition, but rather write a skeleton and then add stuff to turn it into a definition. However, if you don't get the definition working, you'll still get partial credit for a correct skeleton.

General skills:

Total:         /300