From: "Collins, Justin" <collinsj@...>
Date: 2005-12-16T18:38:24+09:00
Subject: Re: Ruby tail recursion

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I wouldn't really call it optimization (although I guess it is), it's =
more like implementing them in such a way that you get around the =
limitations of computer memory. (As opposed to just making them run =
faster or something.) It doesn't really have anything to do with =
efficiency in that sense.

Code like:

def fun(x)
    fun(x)
end

fun(10)

should run forever, like it would in a language like Scheme or Lua. A =
function calls itself, which calls itself, for infinitly. Unfortunately, =
Ruby does not currently work that way.

It's not that Ruby doesn't work "right" in this case, it just runs into =
the limits of hardware (the size of the stack). The "proper" way of =
implementing tail calls would never use the stack, so it wouldn't be an =
issue.

By the way, is there a particular reason why tail calls aren't =
implemented that way?


-Justin


-----Original Message-----
From: ruerue@purr.magical-cat.org on behalf of Eero Saynatkari
Sent: Thu 12/15/2005 7:55 PM
To: ruby-talk ML
Subject: Re: Ruby tail recursion
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On 2005.12.16 12:41, Mark Ericson <mark.ericson@gmail.com> wrote:
> In another thread someone mentioned tail recursion doesn't work right
> in Ruby.   Could someone please expand upon that?

The current interpreter does not do tail-recursion optimization.
This means that deeply recursive operations are not as efficient
as they could be.


E=20


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