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CHAPTER 4. SCHEME SERVLETS

gram which simply returns the date. We assume this is stored in a file named

 date.servlet  stored in the  scheme  folder of the server directory. This file

contains the following lines:

; date.servlet    returns the current time and date

; lines beginning with a semicolon are comments

(Date.)

The first two lines are comments (as they begin with a semicolon) and so are

ignored by Scheme. The second line is a Scheme expression which returns the

current local date and time

1

. To view this servlet, one must visit the URL:

http://MY.DOMAIN.EDU:8080/scheme/date.servlet

where MY.DOMAIN.EDU is the domain name of the scheme server you are using.

If you have installed a Scheme server on your home computer, then you can use

the IP address of your home computer in place of MY.DOMAIN.EDU or you can

use the  self loop  IP address

127.0.0.1

which always refers to the computer itself. Visiting this address with a standard

browser will bring you to page that contains the current time and date:

Sun Jan 20 07:46:44 EST 2002

The expression (Date.) is an example of a Scheme expression. It is an invoca 

tion of the Date. procedure with no arguments.

4.2

Arithmetic Expressions in Scheme

Another simple example of a servlet is the following which we assume is stored

in a file named sumToTen.servlet:

; sumToTen.servlet    this returns the sum of 1 to 10

(+ 1 2 3 4 5 6 7 8 9 10)

When one visits this servlet with a browser, the server evaluates this expres 

sion and applies the addition operator + to the arguments that follow it in the

parenthesized list. The result that is return to the browser is the number

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In a way the scheme server can be viewed as a calculator, where you put the

expression you want to compute into a file and when you view the file with a

browser it will evaluate that expression and return your answer. A slightly more

complex example is the following:

1

Actually, (Date.) returns a  Date  object representing the current time and date. This

Date object is turned into a string representing the date in the local dialect.