On Thu, Jan 1, 2009 at 6:40 PM, Christian Vest Hansen
<[email protected]> wrote:
>
> On Thu, Jan 1, 2009 at 11:48 PM, Chouser <[email protected]> wrote:
>>
>> On Thu, Jan 1, 2009 at 2:47 PM, Rock <[email protected]> wrote:
>>>
>>> Given that there's nothing like letrec in Clojure, and that let acts
>>> like let* in CL, I gather that local recursive functions are possible
>>> whereas local mutually recursive ones are not. Is that correct? If so,
>>> will they ever be in the future?
>>
>> I assume you meant "are not possible". I think someone previously
>> posted a letrec macro using something he called a "Y* combinator". I
>> don't know what that is, but he said it was slow.
>>
>> Here's another way. Nothing about it is pretty, but it is a
>> possibility:
>>
>> (let [my-even-atom (atom nil)
>> my-even? (fn [i] (@my-even-atom i))
>> my-odd? (fn [i]
>> (if (zero? i)
>> false
>> (@my-even-atom (dec i))))]
>> (swap! my-even-atom
>> (constantly (fn [i]
>> (if (zero? i)
>> true
>> (my-odd? (dec i))))))
>> (my-odd? 4))
>
> I don't get this listing. You define my-even? but do not use it?
Good point. I included a convenience function and forgot to use it.
Replace the second "@my-even-atom" with "my-even?":
(let [my-even-atom (atom nil)
my-even? (fn [i] (@my-even-atom i))
my-odd? (fn [i]
(if (zero? i)
false
(my-even? (dec i))))]
(swap! my-even-atom
(constantly (fn [i]
(if (zero? i)
true
(my-odd? (dec i))))))
(my-odd? 4))
--Chouser
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