On Wed, May 29, 2013 at 11:22 PM, Michele La Monaca
<[email protected]> wrote:
> 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))))
>
I think this one can't be beaten:
(named-let* loop ((len (string-length buf))
(i (+ 1 (random len)))
(ch (string-ref buf (- i 1))))
(display ch)
(if (< i len)
(loop len (+ i 1) (string-ref buf i))))
Ciao,
Michele
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