Comp210: Principles of Computing and Programming
Fall 2004 -- Lab #1: Getting Started - DrScheme, Design Recipe   

On the Owlnet PC's, 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 RCC 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\hwXX 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. Enter (or cut/paste) the following into definition window, including:

   
               (+ 2 7)
   
               (* (+ 2 7) 3)
   
   
   
               ; owe: nonneg-num -> nonneg-num
   
               ; Return the amount owed for eating slices slices.
   
               ;
   
               (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. (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.

   The PC and Mac versions of DrScheme use their respective standard keyboard shortcuts instead. (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 Execute 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 Execute, 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 Execute 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. Alternatively, there are keyboard equivalents listed in this menu.

2. Verify your steps by clicking Execute.

3. Once you've used this to verify your steps, put the steps in comments, rather than deleting them. (You'll find that later you might fix a bug, and you want to re-use these as test cases.)

1. From your home directory, type the UNIX command

   
               ls -l
   
               

   You should see a directory called comp210, created by the previous step. If you don't, tell one of the lab assistants.

2. Change directory into the comp210 directory with the UNIX command

   
               cd comp210
   
               

3. Make a directory called Labs by typing

   
               mkdir Labs
   
               

4. Change directory into the Labs directory.
5. Make an Lab01 directory for this lab.
6. Change directory into the Lab01 directory.

1. Enter
   

       drscheme

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

2. In DrScheme for UNIX, some handy the keyboard shortcuts include the following:
   • Control-p (previous line),
   • Control-n (next line),
   • Control-b (back character),
   • Control-f (forward character),
   • Control-a (start of line), and
   • Control-e (end of line).
3. Under UNIX, we recommend using the Mozilla browser, started by the command mozilla. If you have any trouble, ask a labbie during office hours, or contact the staff of the information desk in Mudd.
4. Always "log out" from your UNIX account when you are done and leaving. Otherwise, someone can use your account, e.g., to copy or delete your assignments. One way is to type logout in the "console window" which is labeled. You do not need to exit any other programs first, but be sure to save any important changes first.
5. The rest is the same as in the Windows operating system. except that you should save your work in your ~/comp210/Labs/Lab01/ directory. Be sure to use a filename that has a .scm extension.