Programming Interactive Web Scripts

6 Feb 2002

PL Day 1

Programming Interactive Web Scripts

Matthias FelleisenPLT

6 Feb 2002

PL Day 2

PLT

• principles of program design– introductory– script development

• principles of programming languages– design – analysis – correctness

• programming environments & tools

6 Feb 2002

PL Day 3

PLT: First Session

• principles of program design– introductory– script development: dynamic Web content

• principles of programming languages– design – analysis – correctness

• programming environments & tools

6 Feb 2002

PL Day 4

Dynamic Web Content

• USA Today says: “… more than half the pages on the Web are generated on demand.” (July 2000)

• Why? – connection to up-to-date database – determining consumer information – on-line experiments– games

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PL Day 5

Dynamic Web Content

• Technology: Programming, Contents

• Programming first: – CGI– Java Servlets

• Contents first– Active Server Pages– Java Server Pages

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PL Day 6

Dynamic Web Content

• What is a CGI script? a servlet? How do they work? Why is it difficult to design interactive ones?

• Can we automate their development?

• What does this teach us about GUI dialogues in general?

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PL Day 7

The Common Gateway Interface

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PL Day 8

http://www.ccs.neu.edu/cgi-bin/goto.pl

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PL Day 9

Interactive Web Scripts

• Some URLs point to programs.

• The server invokes the program, which writes a page to the standard output port and then terminates.

• The server sents the page to the client that requested the URL.

6 Feb 2002

PL Day 10

Interactive Web Scripts: Hello World

(printf "My First CGI Page~n”)(printf "Hello World")

Plain Program

(output-http-headers)

(write-xml/content (xexpr->xml '(html (title "My First CGI Page") (body

"Hello World"))))

Web Script

6 Feb 2002

PL Day 11

Interactive Web Scripts: Server Status


(write-xml/content (xexpr->xml `(html (title "Server Status") (body ,(read-line (first (process "uptime")))))))

(printf "Server Status: ~a~n" (read-line (first (process "uptime")))))))

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PL Day 12

Interactive Web Scripts: Multiply-by-10.com


(define (get-number) (get-binding ‘NUM (bindings)))

(write-xml/content (xexpr->xml `(html (title "Multiply-by-10.com") (body

"the result is: " ,(* (get-number) 10)))))

(define (get-number) (printf "Enter a number ") (flush-output) (read))

(printf "Multiply-by-10.com")(printf "the result is: ~a" (* (get-number) 10) )

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PL Day 13


<html> <head><title>Multiply-by-10.com</title></head> <body> <h1>Multiply</h1>

<form method="get" action="http://www. .../mult-by-10.ss"> Enter a number <input type="text" name= "NUM" value="0"> </form> </body></html>

Where do babies come from?

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PL Day 15

Interactive Web Scripts: Multiply.com

(output-http-headers)… (write-xml/content (xexpr->xml `(html (title "Multiply.com") (body

"the result is: " ,(* (get-number)

(get-number))))))

(define (get-number) (printf "Enter a number ") (flush-output) (read))

(printf "Multiply.com")(printf "the result is: ~a" (* (get-number) (get-number)) )

6 Feb 2002

PL Day 16

Interactive Web Scripts: DontMultiply.com

• A CGI script terminates after producing a page.

• To query the consumer, the script must produce a page with a form.

• Ergo: To interact, a CGI program must terminate.

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PL Day 17

Interactive Web Scripts: DontMultipy.com

The natural structure of an interactiveWeb program doesn’t work naturallywith the Common Gateway Interface.

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PL Day 18

Interactive Web Scripts: Interaction

• Current solution: programmers invert program by hand.

• A program with N interaction points becomes a set of N programs.

• The programs communicate all necessary data “manually”.

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PL Day 19

Interacting with Web Scripts

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PL Day 20


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PL Day 22


And now we go BACK:

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<html> <head><title>Multiply</title></head> <body> <h1>Multiply</h1>

<form method="get" action="http://www. .../multiply.ss"> Enter a number <input type="text" name= " NUM" value="0"> </form> </body></html>

6 Feb 2002

PL Day 25

Interactive Web Scripts: cgi-first.ss


(write-xml/content (xexpr->xml `(html (title "The Multiply Page") (body `(form ([method "get"][action "http://.../cgi-second.ss"])

(p "Enter the second number") (input ([type "hidden"][name "first"] [value ,(get-number)])) (input ([type "text"] [name "second"][value "1"])))))))

6 Feb 2002

PL Day 26


<html> <head><title>Multiply</title></head> <body> <h1>Multiply</h1>

<form method="get" action="http://www. .../multiply.ss"> Enter the second number <input type="text" name= "second" value="0"> <input type= "hidden" name= "first" value= ”XXXXXX."> </form> </body></html>

6 Feb 2002

PL Day 27

Interactive Web Scripts: cgi-second.ss


(write-xml/content (xexpr->xml `(html (title "The Multiply Page") (body

"the result is: ",(* (get-number 'first) (get-number ’NUM))))))))

6 Feb 2002

PL Day 28

Interactive Web Scripts and Continuations

(define multiply (lambda (x y) (* x y)))

(define multiply (lambda (x) (lambda (y) (* x y))))

(define multiply-by-22 (lambda (y) (* 22 y)))

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PL Day 29


cgi script consumer cgi script consumer

the back button

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PL Day 30


cgi script consumer cgi script consumer

the back button

cloning

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PL Day 31

PLT’s Interactive Web Script

• Solution 1: Design Web server that supports coroutining. Use continuation objects. Graunke et al. ESOP 2001

• Solution 2: Design transformation that automatically inverts programs with N interaction points into N programs. Graunke et al. ASE 2001 & Jacob Matthews PL Day 2002

6 Feb 2002

PL Day 32

PLT’s Interactive GUI Scripts

• Generalize this technique to certain GUI programs.

• Graunke and Krishnamurthi, ICSE 2002. Graunke PL Day 2002.

Programming Interactive Web Scripts

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