CSC153, Class 14: CGI

Overview:
* Short introduction to CGI
* Q&A
* Lab

Notes:
* Exam 1 tomorrow
* Read "Pairs and Pair Structures"
* Sorry that none of you attended the strategic planning meeting
* Any questions on strings?

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CGI Idea: 
* Rather than just fetching prebuilt pages (and images and ..)
  from the Web, you might want to run programs to generate
  those pages:
* These programs probably need inputa
* Why?
  + Get information from a database
  + Get information from a user (to store in a global
    surveillance system so that we can eliminate terrorism)
  + We might want to provide students with a program that
    gives answers to the quadratic formula

CGI stands for "Common Gateway Interface"

Question: Can you have one Scheme file serve multiple 
purposes?

Reminder:  On the Web page (in HTML) that serves as input
you write

<form method="get" action="dual-purpose.cgi">
<input type="hidden" name="whattodo" value="alpha">
...

</form>

<form method="get" action="dual-purpose.cgi">
<input type="hidden" name="whattodo" value="beta">

</form>

IN Scheme

(define page
  (lambda ()
    (let ((whattodo (get-cgi-variable 'whattodo "")))
      (cond
        ((equal whattodo "alpha") (do-task-1))
        ((equal whattodo "beta")  (do-task-2))
        (else (crash-and-burn-but-nicely))))))

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Preliminaries to get this lab to work

(1) Open a terminal window (computer screen with foot)

(2) Type the following

mkdir public_html
chmod a+x .
chmod a+r public_html
chmod a+x public_html

There is a period on the second line
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REFLECTION

* Too many 153 students are addicted to a twenty-year old movie
* It's very depressing that people whose profession is writing
  instructions can't.  (E.g., why can't CS faculty write clear
  instructions?)