[plt-scheme] why local? (just curious)

Sorry but... why for n < 6?



Shriram Krishnamurthi schrieb:
>> Now I've tried to think up an example myself in which both is present -
>> as I can't get at anything sensible, I just put some sequential
>> assignment in the beginning of the classic even-odd-letrec-example:
>>
>> (define test
>>  (lambda (n)
>>    (letrec ((start-value n)
>>             (zero (- start-value start-value))
>>             (even? (lambda (n) (if (= n zero) #t (odd? (- n 1)))))
>>             (odd? (lambda (n) (if (= n zero) #f (even? (- n 1))))))
>>      (odd? n))))
>>
>> (test 333)
>>     
>
> The meaning of this program is undefined according to RnRS for n < 6.
> Which means: In some implementations, it produces the answer you
> expect.  In other implementations, it yields an error.  In still other
> implementations, it might produce a different answer (or undefined, or
> error) depending on the phase of the moon.
>
> Shriram
>
>