[racket] Basic Racket Question

On Wed, Dec 22, 2010 at 9:43 AM, Sayth Renshaw <flebber.crue at gmail.com>wrote:

>
>
> On Wed, Dec 22, 2010 at 2:04 AM, Stephen Bloch <sbloch at adelphi.edu> wrote:
>
>>
>> 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
>> sbloch at adelphi.edu
>>
>>
> Firstly thank you very much for the feedback and ideas its very
> appreciated.
>
> I am following the book again and your examples but i am rewriting examples
> so I am learning it.
>
> I came to this as a solution based on feeedback but it is erroring on the
> word gross as part of my netpay function. Do i need to define the gross
> function in my netpay function?
>
>
>  (define tax-rate 0.15)
>  (define pay-rate 12)
>  (define (gross hours)
>    (* hours pay-rate))
>
>  (define (netpay gross tax-rate)
>    (gross (- tax-rate)))
>
> Not quite grabbing something intrinsic,  unfortunately Norman this is the
> start of the book..If I have defined gross function as suggested earlier why
> can't my netpay function use it?
>

see ultimately a version like this makes the most sense to me but it won't
allow defined functions. I keep getting this error.

function call: expected a defined function name or a primitive operation
name after an open parenthesis, but found a function argument name

This is my preferred version.

 (define tax-rate 0.15)
 (define pay-rate 12)
 (define (gross hours)
   (* hours pay-rate))

 (define (netpay gross tax-rate)
   (-(gross)(* gross tax-rate)))
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