Assuming you haven't done so for a previous course, create a WebCT account for yourself. In this course, you'll use that for two features: online quizzes and accessing your grades.

On the Owlnet PCs, your "My Documents" folder is the same location as your "U:" drive, which is the same location as your Unix login directory.

We will refer to your U: drive, as this is more closely related to how your computer in your room might be set up (ask your college's CCA how to "map" your Unix account into your personal computer).

1. Make a folder in your U: drive called Comp210.
2. Make a sub-folder in Comp210 called Labs.
3. Make a sub-folder in Labs called Lab01.
4. Save all your Lab01 work to this folder.

For homeworks, make a corresponding Comp210\Homeworks\HWnn folder.

1. Start the DrScheme program., which can be found in the Start menu under Program\Applications\PLTScheme.
2. If this is the first time you've run DrScheme, it will ask you your preferred language, and the Scheme language level; the latter should be "Beginning Student". This level makes DrScheme catch more errors for you: namely, errors which are technically legal Scheme, but are probably not what you really want early in the course.

1. Type (or cut/paste) the following into definition window, including:

   (+ 2 7)
   
   (* (+ 2 7) 3)
   
   ; owe: nat -> num
   ; Returns how much money you owe for eating the given number of
   ; slices of pizza.
   ;
   (define (owe slices)
     (* (/ 12 8) slices))
               

   Observe that DrScheme helps you with the indentation if you use the Return key in appropriate places. It also "bounces" the cursor to visually match the closing parenthesis with the corresponding opening parenthesis.
2. We included comments before each function definition, explaining what it is supposed to do. DrScheme ignores the comments, but you, your grader, your boss, etc., can read them. Soon, we'll provide more guidance on what to say in your comments.

   ; One form of comments is anything following a semicolon
   ; up to the end of the line.
               

   #|
     Another form of comments is anything between these
     two matching markers.
   |#
               

   You can also go to the Special menu, choose Insert comment box. You are welcome to do this, but one caveat: if DrScheme saves a file which includes a fancy comment box, the file will not be saved in plain-text format. (This is only an issue if you want to open or print the file with a different program later.)
3. Edit your definitions or comments some. You can use the mouse, the arrow keys, backspace, and standard keyboard shortcuts to move the cursor around. Also, the PC, Mac, and Unix versions of DrScheme each use their respective standard keyboard shortcuts. (You can look in the Edit menu under Keybindings for the complete list.)
4. Load the definitions into the interaction window by clicking on the Run button. If DrScheme detects any syntactic errors, it will give you an error message in the interactions window and highlight the error in the definitions window.
5. Use those definitions by typing in the interaction window some Scheme expressions using those definitions. E.g.,

   (owe 5)
   
   (owe 7)
               

6. Save your work in your U:\comp210\Labs\Lab01\ directory. Be sure to use a filename that has a ".scm" extension. You don't need to turn in your lab work. In fact, you don't have to save it, but we recommend it so that you can look at it again.
7. Finally, intentionally introduce an error (or, what you think will be an error), press Run, and see what error message is given. We'll go around the room to see what different error messages people get. Do the error messages tend to make sense?

1. Place an example use or two of your functions in the definitions window, after the appropriate definitions. For example,

   (owe 10)
               

2. Click on the Step button. This brings up a new stepper windows which will show how DrScheme calculates the answer.
3. Use the stepper's button to look through the evaluation. At each step, it shows what part of the code needs to be evaluated next, and what the result is.

"Hand-evaluation" is just you doing the same thing as DrScheme's stepper. It is useful to convince yourself that you know what is supposed to happen, independently of having DrScheme help you.

1. Hand-evaluate a few example expressions, and type in each of the small steps you would make to calculate the result. Type these in the definitions window after your definitions. For example,

   ; Hand-evaluation:
   
   (owe 10)
   
   (* (/ 12 8) 10)
   
   (* 3/2 10)
   
   15
               

   This is just high school algebra, successively simplfying expressions, until you reach a final, simple value.
   • What do you hope to see, when you Run all these expressions? What would you see if there were a mistake?
   • While you are doing this, it is often helpful to copy the previous step, and edit this copy for the current step. This can save you some typing, and it helps eliminate mistakes. You'll want the Copy and Paste features in the Edit menu.
2. Verify your steps by clicking Run.
3. Once you've used this to verify your steps, put the steps in comments, rather than deleting them. (Later, you might change the code, and you want to re-use these as test cases.)

Before you do anything in your Unix account for Comp210, you should "register" for the course. This has nothing to do with the registrar. This will change your programming environment slightly to access course software more easily.

1. After you have logged in, type at a shell prompt,

   register comp210
               

   (followed by the Return key, like any Unix command), and answer yes to the questions.
2. Logout and login again, so that the changes take affect.

You won't need to do this ever again.

Now you can start DrScheme by typing

drscheme
        

at a shell prompt. If this complains about a file not found, then register didn't work. Use ~comp210/bin/drscheme instead.