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Re: Something is rotten in Denmark...

From Nobody <nobody@nowhere.com>
Subject Re: Something is rotten in Denmark...
Date 2011-06-03 14:07 +0100
Message-Id <pan.2011.06.03.13.07.40.156000@nowhere.com>
Newsgroups comp.lang.python
References (5 earlier) <mailman.2374.1306948289.9059.python-list@python.org> <2_AFp.30000$241.24052@newsfe07.iad> <4de71c42$0$29983$c3e8da3$5496439d@news.astraweb.com> <87zkm0qyze.fsf@dpt-info.u-strasbg.fr> <94qlhsFkriU1@mid.individual.net>
Organization Zen Internet

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On Fri, 03 Jun 2011 11:43:54 +1200, Gregory Ewing wrote:

>> But going against generally accepted semantics should at least
>> be clearly indicated. Lambda is one of the oldest computing abstraction,
>> and they are at the core of any functional programming language.
> 
> Yes, and Python's lambdas behave exactly the *same* way as
> every other language's lambdas in this area. Changing it to
> do early binding would be "going against generally accepted
> semantics".

In Lisp, it depends upon whether the free variable is bound:

	$ clisp
	[1]> (setq f (lambda (x) (+ x i)))
	#<FUNCTION :LAMBDA (X) (+ X I)>
	[2]> (setq i 7)
	7
	[3]> (apply f (list 4))
	11
	[4]> (setq i 12)
	12
	[5]> (apply f (list 4))
	16
	^D
	$ clisp
	[1]> (let ((i 7)) (setq f (lambda (x) (+ x i))))
	#<FUNCTION :LAMBDA (X) (+ X I)>
	[2]> (apply f (list 4))
	11
	[3]> (setq i 12)
	12
	[4]> (apply f (list 4))
	11
	^D

If the variable is bound, then the lambda creates a closure.

And Python behaves the same way:

	> f = (lambda i: lambda x: x + i)(7)
	> f(4)
	11
	> i = 12
	> f(4)
	11

	# If you really want a "let", this syntax is closer:
	# f = (lambda i = 7: lambda x: x + i)()

The original semantics (from the lambda calculus) don't deal with the
concept of mutable state.

> If anything should be changed here, it's the for-loop, not lambda.

Right. The for loop should bind the variable rather than set it.

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Thread

Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 01:48 -0500
  Re: Something is rotten in Denmark... Chris Rebert <clp2@rebertia.com> - 2011-05-31 00:00 -0700
  Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 01:35 -0600
  Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-31 13:08 +0300
    Re: Something is rotten in Denmark... Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-05-31 12:48 +0200
      Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-31 15:15 +0300
  Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-05-31 13:11 -0400
    Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 15:18 -0500
      Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 16:24 -0600
      Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-05-31 19:14 -0400
        Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 19:09 -0500
          Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-01 13:11 -0400
            Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-01 19:40 -0500
              Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-01 19:50 -0500
                Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 04:37 +0000
              Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 05:14 +0000
                Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-02 18:02 +1000
                Re: Something is rotten in Denmark... Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-06-02 13:00 +0200
                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-02 15:51 +0300
                Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-02 15:43 -0400
                Re: Something is rotten in Denmark... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-03 11:43 +1200
                Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-02 19:24 -0700
                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-03 09:17 +0300
                Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-05 03:54 -0700
                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-05 15:03 +0300
                Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-05 05:26 -0700
                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-05 16:10 +0300
                Re: Something is rotten in Denmark... Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-06-03 10:30 +0200
                Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-03 11:53 -0600
                Re: Something is rotten in Denmark... Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-06-03 12:35 +0200
                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-03 14:07 +0300
                Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-03 15:38 -0500
                Re: Something is rotten in Denmark... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-04 12:40 +1200
                Re: Something is rotten in Denmark... Nobody <nobody@nowhere.com> - 2011-06-03 14:07 +0100
                Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 10:44 -0500
                Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 10:55 -0500
                Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 17:22 +0000
                Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-02 11:43 -0600
              Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-02 02:02 -0400
                Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 11:02 -0500
  Re: Something is rotten in Denmark... Martin Manns <mmanns@gmx.net> - 2011-05-31 23:14 +0200
    Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 15:47 -0600
      Re: Something is rotten in Denmark... Martin Manns <mmanns@gmx.net> - 2011-06-01 02:57 +0200
    Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 16:53 -0500
      Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 17:06 -0500
      Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-01 08:39 +1000
      Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-01 08:40 +1000

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