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CHAPTER 4. SCHEME SERVLETS

Exercise 8 Write a servlet  sumtoN.servlet  which finds the sum of the num 

bers from 1 to N using the formula

1 + 2 + 3 + . . . + N = N   (N + 1)/2

and use it to find the sum from 1 to 100 (You should get 5050).

Exercise 9 Write a servlet  tip.servlet  which calculates the tip required for a

meal assuming that you tip at the 15% rate.

4.9

Giving names to values using let*

When processing complex formulas it is often helpful to break the formula into

pieces and to give names to each individual piece. For example, the body mass

index provides a rough measure of whether your are overweight. The formula

consists of dividing your weight in kilograms by the square of your height in

meters. The following servlet computes your BMI by first converting your weight

in pounds to your weight in kilograms, and your height in inches to your height

in meters, then it applies the formula:

; BMI.servlet

(servlet (w h)

(case w

((#null) {Enter data using ?w=170&h=68})

(else

(let* (

(k

(/ w 2.2))

; weight in kilograms

(m (/ h 39.36))

; height in meters

(bmi (/ k (* m m)))

)

{If your weight is [w] pounds 

and your height is [h] inches,

 Then your BMI is [bmi]. 

Note: a BMI over 30 is considered

medically dangerous}))))

The let* expression above provides temporary names k, m, and bmi for the

computed values. The general form of a let* statement is

(let* (

(var1 Expr1)

(var2 Expr2)

...

(varn Exprn)

)

Expr)