On Wed, May 29, 2013 at 11:10 PM, Michele La Monaca
<[email protected]> wrote:
> On Wed, May 29, 2013 at 10:20 PM, Patrick Li <[email protected]> wrote:
>> Hi Michele,
>>
>> I realized after posting my version of named-let*, that you actually
>> *cannot* use it to accomplish all of what you want. For that you do need
>> loop to be a syntactic extension, as mentioned by Jorg.
>>
>> For instance, my named-let* macro would not simplify the example you posted
>> earlier:
>>
>> (let loop ((i (some-function)) (ch (string-ref buf (some-function))))
>> (do-something)
>> (if (some-condition-is-true)
>> (loop (+ i 1)
>> (string-ref buf (+ i 1)))))
>>
>> The key issue underlying this is, when you call (loop), would you like to
>> call it with one or two arguments?
>>
>
> Two. Your macro seems good to me. For example, let's say I want to
> print a string starting from a random position:
>
> (define buf "foobar")
>
> (named-let* loop ((i (random (string-length buf))) (ch (string-ref buf i)))
> (display ch)
> (if (< (+ i 1) (string-length buf))
> (loop (+ i 1) (string-ref buf (+ i 1)))))
>
>
> or even better:
>
> (named-let* loop ((len (string-length buf)) (i (random len)) (ch
> (string-ref buf i)))
> (display ch)
> (if (< (+ i 1) len)
> (loop len (+ i 1) (string-ref buf (+ i 1)))))
>
>
> Michele
Or even even better (or worse depending on your tastes):
(named-let* loop ((len (string-length buf)) (i (random len)) (j (+ 1
i)) (ch (string-ref buf i)))
(display ch)
(if (< j len)
(loop len j (+ j 1) (string-ref buf j))))
:-)
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