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Re: Python and Lisp : car and cdr

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* 2011-06-19T12:20:32-04:00 * Terry Reedy wrote:

> On 6/19/2011 9:24 AM, Steven D'Aprano wrote:
>> No. Each cell in a Lisp-style linked list has exactly two elements,
>> and in Python are usually implemented as nested tuples:
>>
>> (head, tail)  # Annoyingly, this is also known as (car, cdr).
>>
>> where head is the data value and tail is either another Lisp-style
>> list or a marker for empty (such as the empty tuple () or None).

> It should be noted that the head element of any 'list' can also be a
> list' (as with Python lists),

Both the head and tail elements of a cons cell can refer to any Lisp
objects. Cons cell is a general-purpose primitive data type but it is
_often_ used to build lists and trees so the tail element often refers
to another cons cell (or nil that terminates the list).

Let's not forget that Lisp's program code itself is built on such trees
of cons cells. Lisp code itself is represented in this primitive Lisp
data type. That's why Lisp is so powerful in meta programming. It's
trivial to use Lisp functions to create Lisp code.

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Thread

Python and Lisp : car and cdr Franck Ditter <franck@ditter.org> - 2011-06-17 16:45 +0200
  Re: Python and Lisp : car and cdr Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-17 09:29 -0600
  Re: Python and Lisp : car and cdr Nobody <nobody@nowhere.com> - 2011-06-18 15:34 +0100
  Re: Python and Lisp : car and cdr Lie Ryan <lie.1296@gmail.com> - 2011-06-19 16:00 +1000
    Re: Python and Lisp : car and cdr Ethan Furman <ethan@stoneleaf.us> - 2011-06-19 05:56 -0700
      Re: Python and Lisp : car and cdr Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-19 13:24 +0000
        Re: Python and Lisp : car and cdr Terry Reedy <tjreedy@udel.edu> - 2011-06-19 12:20 -0400
          Re: Python and Lisp : car and cdr Teemu Likonen <tlikonen@iki.fi> - 2011-06-19 19:38 +0300
      Re: Python and Lisp : car and cdr Hrvoje Niksic <hniksic@xemacs.org> - 2011-06-19 16:26 +0200
    Re: Python and Lisp : car and cdr Chris Angelico <rosuav@gmail.com> - 2011-06-19 23:23 +1000
    Re: Python and Lisp : car and cdr "Elias Fotinis" <efotinis@yahoo.com> - 2011-06-19 16:24 +0300
    Re: Python and Lisp : car and cdr Ethan Furman <ethan@stoneleaf.us> - 2011-06-19 08:07 -0700
    Re: Python and Lisp : car and cdr Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-06-19 11:36 -0700

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