[plt-scheme] HTDP Section 18 Pragmatics of local, Part 2

Emeka,

When you define a structure, you get several functions associated with
the structure.

In section 18 you have the following definition:

(define-struct star (name instrument))

Based on this definition, you get observers that extract the
components of the function (i.e. star-name and star-instrument). You
also get a function, star?, to determine it its input is a star
structure. For example, (star? (make-star 'Bach 'violin)) returns true
and (star? 4) returns fasle.



On Wed, Apr 22, 2009 at 4:18 PM, Emeka <emekamicro at gmail.com> wrote:
>
> The below code is an example from the HTDP (no yelling ). Could someone
> explain the highlighted part in detail?  I want something that is detailed
> enough because I understand the general idea.
>
> ;; last-occurrence : symbol list-of-star  ->  star or false
>
> ;; to find the last star record in alostars that contains s in name field
>
> (define (last-occurrence s alostars)
>   (cond
>     [(empty? alostars) false]
>
>     [else (local ((define r (last-occurrence s (rest alostars))))
>
>             (cond
>               [(star? r) r]
>
>               [(symbol=? (star-name (first alostars)) s) (first alostars)]
>
>               [else false]))]))
>
> Thanks in advance.
>
> Regards,
> Emeka
>
>
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-- 

Cheers,

Marco