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Groups > comp.lang.python > #93881
| From | Terry Reedy <tjreedy@udel.edu> |
|---|---|
| Subject | Re: A new module for performing tail-call elimination |
| Date | 2015-07-15 17:19 -0400 |
| References | <55a3dcd9$0$3024$426a34cc@news.free.fr> <55A6280C.3090602@rece.vub.ac.be> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.549.1436995214.3674.python-list@python.org> (permalink) |
On 7/15/2015 5:29 AM, Antoon Pardon wrote:
> On 07/13/2015 05:44 PM, Th. Baruchel wrote:
>> Hi, after having spent much time thinking about tail-call elimination
>> in Python (see for instance http://baruchel.github.io/blog/ ), I finally
>> decided to write a module for that. You may find it at:
>>
>> https://github.com/baruchel/tco
>>
>> Tail-call elimination is done for tail-recursion as well as for
>> continuation-passing style (cps) in a consistent syntax for both usages.
>>
>> Any tail-recursive function having the suitable format for being
>> embeddable in the Y combinator can be used here with no change at all
>> (with the main difference that tail-calls will be eliminated), but other
>> continuations can also be added
>
> 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
# which passes this test
print(even(0) is True, odd(0) is False,
even(1) is False, odd(1) is True,
even(2) is True, odd(2) is False,
even(5) is False, odd(5) is True,
even(6) is True, odd(6) is False)
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.
--
Terry Jan Reedy
Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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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