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Re: Python is going to be hard

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On Thu, Sep 4, 2014 at 1:22 PM, Rustom Mody <rustompmody@gmail.com> wrote:
> | Effect-free programming
> | -- Function calls have no side effects, facilitating compositional reasoning
> | -- Variables are immutable, preventing unexpected changes to program data by other code
> | -- Data can be freely aliased or copied without introducing unintended effects from mutation
>
> So to answer your question: print statements are side-effecting and therefore obstruct
> compositional reasoning.

Yeah, fine. One small problem: Computers aren't built to do nothing.
"Effect-free programming" is utterly valueless and purposeless. To
make a program actually useful, you need to have some effect
somewhere. So where do you do that? Where do you permit a function
with side effects?

If you force *everything* to be in the return value, you lose any
possibility of partial results - for instance, if it takes two weeks
to render a ray-traced animation, you actually spend the entire two
weeks building up a single, gigantic return value, which some outside
system (which is presumably allowed to have side effects) then saves
somewhere. In the meantime, you have absolutely no idea how far it's
progressed - no information that it's completed frame 6 and is working
on frame 7, nothing. Because telling the user anything is a side
effect.

And if my function f calls show_status_to_user() which has side
effects, then f has side effects too, and you can no longer reason
purely about f. The impurity that makes for practicality (hey, isn't
there something in the Zen of Python about that?) pollutes upwards
until all you'll have will be pockets of pure functional code that
execute quickly enough to not need any intermediate output. That
doesn't equate to "abolish print", that just means that you separate
the guts from the UI - which is good advice for any system, no matter
what its structure.

ChrisA

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Thread

Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:10 -0400
  Re: Python is going to be hard John Gordon <gordon@panix.com> - 2014-09-03 18:17 +0000
    Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:52 -0400
      Re: Python is going to be hard mm0fmf <none@mailinator.com> - 2014-09-03 22:37 +0100
  Re: Python is going to be hard Rock Neurotiko <miguelglafuente@gmail.com> - 2014-09-03 20:16 +0200
  Re: Python is going to be hard Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-09-03 11:19 -0700
    Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:50 -0400
  Re: Python is going to be hard MRAB <python@mrabarnett.plus.com> - 2014-09-03 19:24 +0100
  Re: Python is going to be hard Skip Montanaro <skip@pobox.com> - 2014-09-03 13:28 -0500
    Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:52 -0400
  Re: Python is going to be hard Ethan Furman <ethan@stoneleaf.us> - 2014-09-03 11:33 -0700
    Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:41 -0400
      Re: Python is going to be hard Ethan Furman <ethan@stoneleaf.us> - 2014-09-03 12:49 -0700
  Re: Python is going to be hard Juan Christian <juan0christian@gmail.com> - 2014-09-03 15:44 -0300
    Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:56 -0400
  Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 14:49 -0400
    Re: Python is going to be hard Ethan Furman <ethan@stoneleaf.us> - 2014-09-03 11:55 -0700
      Re: Python is going to be hard Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-09-03 12:01 -0700
    Re: Python is going to be hard Ian Kelly <ian.g.kelly@gmail.com> - 2014-09-03 13:11 -0600
      Re: Python is going to be hard Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-09-03 15:22 -0400
    Re: Python is going to be hard Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-04 12:11 +1000
  Re: Python is going to be hard Denis McMahon <denismfmcmahon@gmail.com> - 2014-09-03 20:55 +0000
  Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 18:48 -0700
    Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 11:56 +1000
      Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 19:10 -0700
        Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 12:25 +1000
          Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 19:33 -0700
            Re: Python is going to be hard alister <alister.nospam.ware@ntlworld.com> - 2014-09-04 10:29 +0000
              Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-04 06:08 -0700
          Re: Python is going to be hard Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-04 23:25 +1000
            Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 23:55 +1000
      Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 20:22 -0700
        Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 13:49 +1000
          Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 21:11 -0700
            Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 15:02 +1000
              Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 23:23 -0700
                Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 16:39 +1000
                Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-04 06:15 -0700
                Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-04 23:30 +1000
                Re: Python is going to be hard Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-09-04 23:37 +1000
                Re: Python is going to be hard Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-09-04 15:04 +0100
                Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-05 00:08 +1000
                Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-04 19:24 -0700
                Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-05 12:30 +1000
                Re: Python is going to be hard Roy Smith <roy@panix.com> - 2014-09-04 22:51 -0400
                Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-04 19:56 -0700
                Re: Python is going to be hard Chris Angelico <rosuav@gmail.com> - 2014-09-05 13:08 +1000
        Re: Python is going to be hard Ethan Furman <ethan@stoneleaf.us> - 2014-09-03 21:06 -0700
          Re: Python is going to be hard Rustom Mody <rustompmody@gmail.com> - 2014-09-03 21:15 -0700

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