Path: csiph.com!optima2.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!1.eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed7.news.xs4all.nl!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <antoon.pardon@rece.vub.ac.be>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.006
X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'else:': 0.03; 'received:134': 0.05; 'rewrite': 0.07; 'subject:module': 0.09; 'def': 0.13; '11:19': 0.16; 'assignments': 0.16; 'cyclic': 0.16; 'module?': 0.16; 'received:ac.be': 0.16; 'reedy': 0.16; 'true:': 0.16; 'wrote:': 0.16; ';-)': 0.18; 'suppose': 0.22; 'am,': 0.23; 'replacing': 0.23; 'header:In-Reply-To:1': 0.24; 'header:User- Agent:1': 0.26; 'order.': 0.27; 'module.': 0.27; 'tail': 0.29; 'received:be': 0.30; 'rule': 0.33; 'gives': 0.35; 'false': 0.35; 'should': 0.36; 'to:addr:python-list': 0.36; 'pm,': 0.36; 'subject:: ': 0.37; 'two': 0.37; 'version': 0.38; 'does': 0.39; 'subject:-': 0.39; 'to:addr:python.org': 0.40; 'your': 0.60; 'more': 0.63; 'believe': 0.66; 'combining': 0.66; 'pardon': 0.84; 'involved.': 0.91
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AnUFAOZfp1WGuA9G/2dsb2JhbABbhCsBg0i9QIJUAoINAQEBAQEBhS8BAQQjVRELGAICBRYLAgIJAwIBAgFFEwgCiCq5HJEyhHgBAQgCIIEiiiqFDRaCUoFDAQSURodOhEqBQ4Z4jGODYSaDfoM4AQEB
Date: Thu, 16 Jul 2015 09:45:26 +0200
From: Antoon Pardon <antoon.pardon@rece.vub.ac.be>
User-Agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Icedove/31.7.0
MIME-Version: 1.0
To: python-list@python.org
Subject: Re: A new module for performing tail-call elimination
References: <55a3dcd9$0$3024$426a34cc@news.free.fr> <55A6280C.3090602@rece.vub.ac.be> <mo6iq5$vqk$1@ger.gmane.org>
In-Reply-To: <mo6iq5$vqk$1@ger.gmane.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.20+
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.572.1437032728.3674.python-list@python.org>
Lines: 43
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1437032728 news.xs4all.nl 2868 [2001:888:2000:d::a6]:57383
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:93913

On 07/15/2015 11:19 PM, Terry Reedy wrote:
> On 7/15/2015 5:29 AM, Antoon Pardon wrote:
>>
>> Can you explain how you would do mutual recursive functions?
>> Suppose I start with the following:
>>
>> def even(n):
>>      True if n == 0 else odd(n - 1)
>>
>> def odd(n):
>>      False if n == 0 else even(n - 1)
>>
>> How do I rewrite those with your module?
>
> I will not answer for Baruchel's tco module.  However, combining the
> two bodies and following the general rule of replacing tail recursive
> calls with assignments inside a while loop gives us
>
> def even(n):
>     return not odd(n)
>
> def odd(n):
>     while True:
>         if not n:
>             return False
>         else:
>             n  -= 1
>         if not n:
>             return True
>         else:
>             n -= 1
> [ ... ]
>
> I believe that this pattern should work with any set of mutually
> recursive functions that always call each other in cyclic order.  A
> more elaborate version does not have this limitation.
>

Nice of you to illustrate the warping involved.  ;-) 

-- 
Antoon Pardon.