Summary: This lab reviews some mechanics related to the use of
Scheme for CGI Scripts in CSC151.
Useful Files:
Contents:
a. Make sure you've done the reading on CGI.
b. Make copies of
greeting.scm and
greeting.html
in your public_html directory.
c. Create (using gedit or DrScheme) the file
greeting.cgi in your public_html
directory that contains the
following two lines
#!/bin/bash
/home/rebelsky/bin/schemeweb greeting.scm
The lines must be flush against the left margin!
d. Share all three files. You should use a command like the
following for each file (type it in a terminal window).
Don't type the percent sign.
e. Make greeting.cgi executable by typing the following
in your terminal window:
Don't type the percent sign.
Look at
webutils.scm (by following that link).
a. See if you can tell what the following procedures do.
-
paragraph
-
markup
-
form
-
get-cgi-variable
Note
that you can test each procedure by loading the file in DrScheme with
(load "/home/rebelsky/Web/Scheme/webutils.scm")
and then trying sample expressions involving those procedures.
b. See if you can tell how markup accomplishes its task.
a. Open greeting.scm from within DrScheme.
b. Scan through the code and see if you can understand what each
procedure does. Focus on greeting-page and page.
b. Execute greeting.scm.
c. Type (page) and see what happens.
d. Find the code that defines user and change the string
"SamR" to your name.
e. Type (page) and see what happens.
f. Type (greeting-page "Fred") and see what happens.
Things may go seriously wrong in this step and subsequent
steps. Feel free to ask lots of questions.
a. In a Web browser, open
<http://www.cs.grinnell.edu/~yourid/greeting.html>.
b. Enter XXX and click the button.
c. What happens? Can you tell why?
a. Update the body of page to read
(nice-page (get-cgi-variable 'name "Sam")).
b. What do you expect to happen when you execute your modified
code and then evaluate (page) within DrScheme?
c. Verify your answer experimentally.
d. What do you expect to happen when you try the Web interface to your code
(that is, when you enter values on the HTML page and then click the button)?
e. Verify your answer experimentally.
a. Add the following procedure to greeting.scm.
(define custom-page
(lambda (person)
(if (equal? person "Sam")
(hate-page person)
(nice-page person))))
b. Update the body of page to use custom-page
rather than nice-page (or greeting-page).
c. What effect do you expect the change to have?
d. What do you expect to happen when you try the Web interface to your code
(that is, when you enter values on the HTML page and then click the button)?
e. Verify your answer experimentally.
f. What do you expect to happen when you enter SamR
on the Web
interface? How about Sam
?
a. Change the body of page to read
(greeting-page (get-cgi-variable 'person "Jane")).
b. What do you expect to happen when you execute your modified code and
then evaluate (page) within DrScheme?
c. Verify your answer experimentally.
d. What do you expect to happen when you try the Web interface to your code
(that is, when you enter values on the HTML page and then click the button)?
e. Verify your answer experimentally.
f. Fix the error you introduced in step a above.
a. Add a text field to the Web page that prompts for a color.
b. See what happens when someone fills in the color (presumably nothing).
c. Update greeting.scm to store the choice in a variable.
(Hint: Look at what I did for user.)
d. Update the greeting-page procedure to take the selected
color as a second parameter. You must include some comment about the
color in the output from greeting-page.
e. Verify within DrScheme that the new greeting-page
still works.
f. Update page so that it passes both user
and the color on to greeting-page.
g. Test from within your Web browser.
As you may have observed in your experiences on the Web, there are
many different kinds of input device on forms. One popular input
device is the so-called radio button in which someone selects
between a few options by clicking to the left of an option.
You can create those buttons with
<input type="radio" name="XXX" value="Val1">Text
<input type="radio" name="XXX" value="Val2">Text
<input type="radio" name="XXX" value="Val3">Text
Each radio button in a group must have the same name.
For example, here are a collection of buttons that let someone indicate
what their status is at Grinnell. Note that the value specified does
not need to match the text.
<input type="radio" name="status" value="5">President
<input type="radio" name="status" value="4">Administrator
<input type="radio" name="status" value="3">Student
<input type="radio" name="status" value="2">Staff
<input type="radio" name="status" value="1">Faculty
Here's how those buttons appear in a browser:
a. Replace the color field in greeting.html with
some radio buttons.
b. Verify that the CGI script still works with those buttons.
You can also encode hidden
values in your forms. These are
values that you want to pass on to the CGI script but that you
don't want the user to change.
a. Replace the line that reads
<input type="text" name="user" value="">
with one that reads
<input type="hidden" name="user" value="John Doe">
b. What effect do you expect this change to have?
c. Verify your results experimentally.
;
Check with Bobby