On Dec 21, 2010, at 6:50 AM, Sayth Renshaw wrote:
> Doing the netpay of employee tax = 0.15 and pay = hrs *12. From the beginner
> tutorial. I see two ways a simple and a hard way but neither work.
>
> Hard way
>
> (define (hours h)
> (h : number?))
> (define (tax t)
> (= t 0.15))
> (define (payrate p)
> (= p $12.00))
> (define (netpay hours tax payrate)
> (* h p)-(* t(* h p)))
Something else I forgot to mention in my previous message: you're quite right
to want to give names to the tax rate and the hourly pay. The usual way to do
this in Beginner Racket would be
(define tax-rate 0.15)
(define pay-rate 12)
Note that these definitions are OUTSIDE the definition of "netpay".
You can then use these in functions you define. For example, the "inventory"
step of this function definition would become
(define (netpay hours)
; hours a number
; pay-rate a number ($/hour)
; tax-rate a number
...
)
and then the body could use all three of these variable names.
Later in the book, you'll learn another way to do it, using "local variables"
so the names "tax-rate" and "pay-rate" are visible only INSIDE "netpay":
(define (netpay hours)
(local [(define tax-rate 0.15)
(define pay-rate 12)]
; hours a number
; tax-rate a number
; pay-rate a number ($/hour)
...
))
This version doesn't work in Beginning Student Language, though; you need
Intermediate Student Language.
Stephen Bloch
[email protected]
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