Index: Sign Ups, Register, DrScheme, Design Recipe, Step-by-step evaluation, Other basics, Logging out
The main goals of this lab are to ensure that you can
Outside of lab, don't forget to get a homework partner and sign up for a lab section, if you haven't already.
This has nothing to do with the registrar. At a Unix prompt, type
register 210
(followed by the Return key, like any UNIX command)
and answer yes to the questions. This will change your environment
slightly to access course software more easily.
For the changes to take effect, logout and login again.
To do: Start DrScheme by typing
drscheme
in an xterm window.
(If this complains about a file not found, then register
didn't work. Use ~comp210/bin/drscheme instead.)
For home use, you can download DrScheme.
The DrScheme window is divided into two halves. The lower half, or interaction window, is the Scheme "calculator". The top half, or definition window is merely a text editor (which is smart about indenting Scheme, and such).
To do: Verify that the interaction window says "Beginning Student". If it does not, from the Language menu, select Configure Language. From the menu that gives you, select Beginning Student. This 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.
To do: Enter the examples from class into the definition window, including the following one:
(define (owe slices)
(* (/ 12 8) slices))
DrScheme helps you with the indentation if you use the Return key in appropriate places. Observe that DrScheme "bounces" the cursor to visually match the closing parenthesis with the corresponding opening parenthesis. To edit, you can use the mouse, arrow keys, and backspace as you would expect. There are also key strokes that you can learn, such as Control-p, Control-n, Control-b, Control-f, Control-a, and Control-e for moving the cursor around. (PC and Mac versions use their respective standard keyboard shortcuts instead.) Some people prefer using the mouse, while some people prefer using the keyboard.
To do: Now we want to use those definitions. To do so, we first need to "load" those definitions into the calculator part of DrScheme by clicking on the "Execute" button. Now, in the bottom half of the window, type in some Scheme expressions, including some using owe
DrScheme has lots of other features, including a complete manual. There's no need to learn all its features, but we encourage you to explore.
We have begun to discuss these in class, but they will be introduced in full this coming week.
When writing programs, there are lots of things we need to think about. It helps if we have some guidelines to follow that remind us to do these things in the proper order. While following some strict rules can seem annoying at first, in the end it will save you lots of errors and grief. These guidelines will be our design recipes.
Working with unstructured data, like the integers or booleans that we've seen, is relatively simple:
Write the function's contract, purpose, and header.
The contract specifies the function name and what kind of values the function will use as input and output. The purpose is a short statement describing what (not how) the function will calculate. The header is the part of the function definition specifying the function and parameter names.
Type these in the definition window. Put the contract and purpose in comments so that Scheme will ignore them (but, of course, you, your grader, your boss, ... will read them). E.g.,
; owe : nonneg-num -> nonneg-num
; Purpose: owe returns how much money you owe for the given number of
; pizza slices.
(define (owe slices) ...)
or
#|
owe : nonneg-num -> nonneg-num
Purpose: owe returns how much money you owe for the given number of
pizza slices.
|#
(define (owe slices) ...)
Make some examples of what the function should do. You need to make sure you understand what the function is supposed to do before you define it. When applicable, use some of the example data.
Put these in comments also, e.g.,
#|
(owe 0) = 0
(owe 10) = 15
|#
Using the equal sign like this will be convenient later.
Write the function body.
For programs on unstructured data, this is very straightforward, because we are typically given an equation, e.g.,
(define (owe slices)
(* (/ 12 8) slices))
For sets of intervals or other conditional functions, there should
be exactly one condition clause per option.
Test the function. Make sure the previous examples really work.
If you wrote the tests as suggested above, you can test them by uncommenting them, and executing the program again. You'll see the results of the tests together with the expected answers. If your program doesn't work, either fix it now or put that in comments too, to remind yourself to fix it later, and to let your grader/boss/customer/whomever know also.
To do: Follow these steps to define a function calculating the area of a circle, as discussed in class.
Later, we will have additional design recipes for more complicated data and program styles.
To do: Place an example use or two of your functions in the definitions section, after the appropriate definitions. For example,
(owe 10)
To see how DrScheme calculates the answers, press the
Step button. The new stepper window will show you what
part of the code needs to be evaluated next, and what the result is.
The stepper's buttons let you look at each step of the evaluation.
You should be able to do by hand what the DrScheme stepper does.
To do: Hand-evaluate some example expressions. Type in each of the small steps you would make to calculate the result, e.g.,
(owe 10)
= (* (/ 12 8) 10)
= (* 3/2 10)
= 15
Separating each of the steps with an equal sign is a neat little
trick to make things look nice.
You can verify your steps clicking "Execute" -- you should see the
same answer multiple times, once for each step.
(Once you've used this to verify your steps, put it in comments, rather
than deleting it.)
While you are doing this, it is 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. Or, note that there are keyboard equivalents listed in this menu.
Try some other examples, possibly with some other simple definitions.
These things probably won't be covered in lab. Make sure you're familiar with
Newsgroups are electronic bulletin boards where everybody can post and read articles on certain topics. There is a newsgroup specifically for this course, rice.owlnews.comp210. You should read the newsgroup every day, as helpful hints and clarifications are posted there regularly. Also, if you have a question relating to the course, post it to the newsgroup. Similarly if you have an answer for somebody else's question!
In newsgroups, the idea is that once you've read a message, you probably don't ever want to see it again. So your newsreader "marks" an article as read, and next time you read news it only presents you with unmarked articles. (You also have options such as unmarking read articles or looking at all articles.) Most newsgroup-reading programs also group articles by "thread", i.e., grouping articles with any replies.
There are many different news-reading programs you can choose from. Two leading contenders are Netscape and Pine, each of which makes reading news analagous to their way of reading email.
Always "log out" 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.