On Mon, Nov 16, 2015 at 5:24 PM, David Nalesnik <david.nales...@gmail.com>
wrote:
> Hi Simon,
>
> On Sun, Nov 15, 2015 at 12:53 PM, Simon Albrecht <simon.albre...@mail.de>
> wrote:
>
>> Hello,
>>
>> The subject certainly seems cryptic – it’s difficult to summarize, but an
>> example will make it clear immediately.
>> I want to write a scheme procedure, which takes a pair like #'(3 . 7) and
>> returns a list with all the numbers in the range: #'(3 4 5 6 7)
>> How is this done most easily?
>>
>>
> Well, if the numbers are ascending you could do something like:
>
> (define (expand-interval arg)
> (iota (- (1+ (cdr arg)) (car arg)) (car arg)))
>
> (display (expand-interval '(3 . 7)))
>
> If not, something like this would work:
>
(define (expand-interval arg)
(let ((step (if (> (car arg) (cdr arg)) -1 1)))
(iota (1+ (abs (- (cdr arg) (car arg)))) (car arg) step)))
--David
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