Re: [MIT-Scheme-users] how to search a string in lists

[Broseph]

santonoreg wrote:
> 
> Hi,
> 
> I've the following code..
> 
> (define FullList '(
> (define f1 '((name (George))
>                    (address (Kalavrytwn))
>                    (phone 2103333333)))
> (define f2 '((name (Spyros))
>                    (address (Stadiou))
>                    (phone 2102222222)))
> 
> 
> Question: How i can make a function to take as parameters the list, phone
> and search if the phone number exists. Also i want to display the name of
> the phone number owner.
> 
> Thanks in advance,
> 
> Sorry for my bad english!!!! 
> 


Well, if your list is like this:
(((George) (Kalavrytwn) (2103333333))
 ((Spyros) (Stadiou) (2102222222)))

Then you can write something like this:
(define (existing-number? address-book phone-number)
    (if (null? address-book)
        #f
        (let* ((first-contact (car address-book))
                 (first-phone (caddr first-contact))
                 (rest-of-contacts (cdr address-book)))
            (if (equal? first-phone phone-number)
                #t
                (existing-number? rest-of-contacts phone-number)))))

There is probably a prettier way of doing this, and if your list is
presorted with respect to the phone numbers, then you could do a binary
search instead of this linear one. 
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