From: Joel VanderWerf <vjoel@...>
Date: 2004-07-07T03:04:45+09:00
Subject: Re: Functional Ruby (Re: Why I don't use Ruby.)

Mikael Brockman wrote:
> Joel VanderWerf <vjoel@PATH.Berkeley.EDU> writes:
> 
> 
>>Mikael Brockman wrote:
>>
>>>In Scheme, sum would be:
>>> (define (sum xs)
>>>   (if (null? xs)
>>>      0
>>>     (+ (car xs) (sum (cdr xs)))))
>>
>>Ruby doesn't optimize this tail recursion, but Scheme does. That's one
>>way Scheme could be said to be more "functional".
> 
> 
> There's no tail recursion in that function, but you have a point.  TCO
> would be nice, but it's easy to perform the optimization manually.

Oops. Quite right. The (+ ...) prevents that. I think sum can be written 
in a TCO-friendly way though: call a second function sum2 that has two 
args, an accumulator and xs, which recurses with

   (sum2 (+ acc (car xs)) (cdr xs))

Anyway, once you've manually optimized a tail call in ruby, it doesn't 
look very functional any more, does it? Maybe I'm not understanding your 
suggestion...