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Re: A new module for performing tail-call elimination

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From Terry Reedy <tjreedy@udel.edu>
Subject Re: A new module for performing tail-call elimination
Date Thu, 16 Jul 2015 15:34:12 -0400
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On 7/16/2015 3:45 AM, Antoon Pardon wrote:
> 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.  ;-)

Glad you appreciate it. To me, the warping is no more than, and perhaps 
less than, and certainly less obnoxious than, the warping required when 
using Baruchel's tco module.  (Opinions can vary, of course.)  The 
result will definitely run faster than with B's tco.

-- 
Terry Jan Reedy

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Thread

A new module for performing tail-call elimination "Th. Baruchel" <baruchel@no.spam.gmx.dot.com> - 2015-07-13 15:44 +0000
  Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-15 11:29 +0200
    Re: A new module for performing tail-call elimination Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-07-16 18:07 +1000
      Re: A new module for performing tail-call elimination Robin Becker <robin@reportlab.com> - 2015-07-16 10:13 +0100
      Re: A new module for performing tail-call elimination Robin Becker <robin@reportlab.com> - 2015-07-16 10:28 +0100
        Re: A new module for performing tail-call elimination Marko Rauhamaa <marko@pacujo.net> - 2015-07-16 12:56 +0300
      Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-16 12:41 +0200
        Re: A new module for performing tail-call elimination Steven D'Aprano <steve@pearwood.info> - 2015-07-17 04:58 +1000
          Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-17 11:00 +0200
      Re: A new module for performing tail-call elimination Chris Angelico <rosuav@gmail.com> - 2015-07-16 21:11 +1000
      Re: A new module for performing tail-call elimination Jeremy Sanders <jeremy@jeremysanders.net> - 2015-07-16 13:29 +0200
      Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-16 15:35 +0200
      Re: A new module for performing tail-call elimination Chris Angelico <rosuav@gmail.com> - 2015-07-16 23:47 +1000
        Re: A new module for performing tail-call elimination Paul Rubin <no.email@nospam.invalid> - 2015-07-17 20:06 -0700
      Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-16 16:21 +0200
      Re: A new module for performing tail-call elimination Chris Angelico <rosuav@gmail.com> - 2015-07-17 00:27 +1000
      Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-16 17:14 +0200
      Re: A new module for performing tail-call elimination Ian Kelly <ian.g.kelly@gmail.com> - 2015-07-16 10:17 -0600
      Re: A new module for performing tail-call elimination Ethan Furman <ethan@stoneleaf.us> - 2015-07-16 10:54 -0700
      Re: A new module for performing tail-call elimination Ethan Furman <ethan@stoneleaf.us> - 2015-07-16 11:02 -0700
      Re: A new module for performing tail-call elimination Terry Reedy <tjreedy@udel.edu> - 2015-07-16 15:45 -0400
      Re: A new module for performing tail-call elimination Ethan Furman <ethan@stoneleaf.us> - 2015-07-16 12:58 -0700
      Re: A new module for performing tail-call elimination Robin Becker <robin@reportlab.com> - 2015-07-17 09:57 +0100
    Re: A new module for performing tail-call elimination Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-07-16 13:23 +0200
  Re: A new module for performing tail-call elimination Terry Reedy <tjreedy@udel.edu> - 2015-07-15 17:19 -0400
  Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-16 09:45 +0200
  Re: A new module for performing tail-call elimination Terry Reedy <tjreedy@udel.edu> - 2015-07-16 15:34 -0400
    Re: A new module for performing tail-call elimination Marko Rauhamaa <marko@pacujo.net> - 2015-07-16 22:45 +0300
      Re: A new module for performing tail-call elimination Terry Reedy <tjreedy@udel.edu> - 2015-07-17 15:47 -0400
        Re: A new module for performing tail-call elimination Marko Rauhamaa <marko@pacujo.net> - 2015-07-17 23:55 +0300
          Re: A new module for performing tail-call elimination Terry Reedy <tjreedy@udel.edu> - 2015-07-17 20:40 -0400
            Re: A new module for performing tail-call elimination Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-07-19 10:39 +1200
          Re: A new module for performing tail-call elimination Chris Angelico <rosuav@gmail.com> - 2015-07-18 10:47 +1000
          Re: A new module for performing tail-call elimination Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-07-19 10:39 +1200
      Re: A new module for performing tail-call elimination Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-07-19 10:39 +1200
        Re: A new module for performing tail-call elimination Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-07-19 01:09 +0100
        Re: A new module for performing tail-call elimination MRAB <python@mrabarnett.plus.com> - 2015-07-19 01:19 +0100
        Re: A new module for performing tail-call elimination Marko Rauhamaa <marko@pacujo.net> - 2015-07-19 09:29 +0300
  Re: A new module for performing tail-call elimination Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-07-17 10:06 +0200

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