# [racket] Question #3 from Realm of Racket

 From: Alexander D. Knauth (alexander at knauth.org) Date: Mon Jun 30 12:12:40 EDT 2014 Previous message: [racket] Question #3 from Realm of Racket Next message: [racket] Question #3 from Realm of Racket Messages sorted by: [date] [thread] [subject] [author]

```In this program, a world is just an interval.

All of those w s could be replaced with ivl s, because a world is an interval, and the value of the parameter will always be an interval.

However, (I’m guessing) using world or w makes it clear that the functions are meant to be used with big-bang.

They could’ve also named the struct world instead of interval, but interval is a better name because its a lot more descriptive of what it represents.

On Jun 30, 2014, at 11:43 AM, Steve Graham <jsgrahamus at yahoo.com> wrote:

> In Guess My Number I see the following definitions:
>
> (define (smaller w)
>   (interval (interval-small w)
>             (max (interval-small w) (sub1 (guess w)))))
> (define (bigger w)
>   (interval (min (interval-big w) (add1 (guess w)))
>             (interval-big w)))
> (define (guess w)
>   (quotient (+ (interval-small w) (interval-big w)) 2))
> (define (render w)
>   (overlay (text (number->string (guess w)) SIZE COLOR) MT-SC))
> (define (render-last-scene w)
>   (overlay (text "End" SIZE COLOR) MT-SC))
> (define (single? w)
>   (= (interval-small w) (interval-big w)))
>
> Why is w (which is world?) included as a parameter?  For instance in guess, it seems the only thing needed to calculate it is access to the values of interval.
>
>
> Steve
>
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users

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