Re: Functional programming

References	(4 earlier) <3b54a279-03a1-4a81-a428-ecad6eb16036@googlegroups.com> <mailman.7641.1393855219.18130.python-list@python.org> <216bb5f4-32c4-4f86-a9f4-1b0dd37a2a81@googlegroups.com> <mailman.7644.1393856584.18130.python-list@python.org> <0129a5b9-b85f-4ad5-b5e2-bfb2a48041d5@googlegroups.com>
Date	2014-03-04 02:01 +1100
Subject	Re: Functional programming
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.7647.1393858917.18130.python-list@python.org> (permalink)

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On Tue, Mar 4, 2014 at 1:38 AM, Rustom Mody <rustompmody@gmail.com> wrote:
> If you want the (semantic) equivalent of python's [1,2,'foo']
> you need to make an explicit union Int and String and its that
> *single* union type's elements that must go in.
>
> In all cases its always a single type. And so
> sum([1,2,[3])

Okay. That's how the declaration goes, then. So how do you tell it
that 1 isn't an Int, it's a member of the union of Int and String? How
do you create a list which has [Int_String(1), Int_String(2)] and is
therefore allowed to be added to [Int_String('foo')] ? Can you do that
with literals?

This is why it's tricky to put rules in based on type inference. The
programmer's intent isn't in the picture. If Python ever acquires that
kind of restriction ("here's a list that can contain only this type /
these types of object"), I would hope that it's left up to the
programmer, not the compiler, to stipulate. That's how it is with Pike
(if you just say "array", it can take anything), and that's the only
way to be sure the programmer doesn't have to fight the language.

You said earlier

>> On Tue, Mar 4, 2014 at 1:08 AM, Rustom Mody wrote:
>> > If 'integer-less-than-3' were a type then yes there would be this
>> > problem. More generally, if types could overlap then automatic
>> > type-inference is impossible

The type "Int" overlaps with the type "Union of Int and String". How
is that resolved? Type inference ignores unions? That's the only way I
can think of. Hence the original difficulty of type-inferring on a
list that isn't complete yet.

ChrisA

Thread

Re: Functional programming Ned Batchelder <ned@nedbatchelder.com> - 2014-03-02 20:27 -0500
  Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 03:45 -0800
    Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-03 23:20 +1100
      Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 05:48 -0800
        Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 05:51 -0800
        Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 01:00 +1100
          Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 06:08 -0800
            Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 01:23 +1100
              Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 06:38 -0800
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 02:01 +1100
                Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 07:28 -0800
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-03 17:27 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 05:37 +1100
                Re: Functional programming Steven D'Aprano <steve@pearwood.info> - 2014-03-04 05:35 +0000
                Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 21:59 -0800
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 17:04 +1100
                Re: Functional programming Rustom Mody <rustompmody@gmail.com> - 2014-03-03 22:20 -0800
                Re: Functional programming Steven D'Aprano <steve@pearwood.info> - 2014-03-04 08:56 +0000
                Re: Functional programming Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2014-03-04 11:56 +0100
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 11:47 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 00:01 +1100
                OT Sine Rule [was Re: Functional programming] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 14:25 +0000
                Re: OT Sine Rule [was Re: Functional programming] Tim Chase <python.list@tim.thechases.com> - 2014-03-04 08:37 -0600
                Re: OT Sine Rule [was Re: Functional programming] Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-04 14:42 +0000
                Re: OT Sine Rule [was Re: Functional programming] Chris Angelico <rosuav@gmail.com> - 2014-03-05 02:06 +1100
                Re: OT Sine Rule [was Re: Functional programming] Tim Chase <python.list@tim.thechases.com> - 2014-03-04 09:21 -0600
                Re: Functional programming Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2014-03-05 09:59 +0100
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 21:49 +0200
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 07:01 +1100
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 22:50 +0200
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 08:06 +1100
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 23:21 +0200
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 08:26 +1100
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 23:43 +0200
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 08:52 +1100
                Re: Functional programming Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-03-05 12:57 +1300
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 02:11 +0200
                Re: Functional programming "BartC" <bc@freeuk.com> - 2014-03-04 13:30 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 00:47 +1100
                Re: Functional programming Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-04 14:05 +0000
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 14:55 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 02:13 +1100
                Re: Functional programming MRAB <python@mrabarnett.plus.com> - 2014-03-04 17:07 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 01:17 +1100
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 15:18 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 02:28 +1100
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 15:45 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 03:04 +1100
                Re: Functional programming Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2014-03-05 10:09 +0100
                Re: Functional programming "BartC" <bc@freeuk.com> - 2014-03-05 11:28 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-05 23:04 +1100
                Re: Functional programming Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 14:11 +0200
                Re: Functional programming Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-03-04 11:06 +1300
                Re: Functional programming Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:31 +1100
                Re: Functional programming Grant Edwards <invalid@invalid.invalid> - 2014-03-04 14:59 +0000
                Re: Functional programming Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 15:22 +0000
                Re: Functional programming Chris Angelico <rosuav@gmail.com> - 2014-03-04 09:42 +1100
                Re: Functional programming Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 10:52 +1100
                Re: Functional programming "BartC" <bc@freeuk.com> - 2014-03-04 09:41 +0000
            Re: Functional programming 88888 Dihedral <dihedral88888@gmail.com> - 2014-03-03 16:35 -0800

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