Re: Functional programming

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Date	2014-03-04 01:23 +1100
Subject	Re: Functional programming
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.7644.1393856584.18130.python-list@python.org> (permalink)

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On Tue, Mar 4, 2014 at 1:08 AM, Rustom Mody <rustompmody@gmail.com> wrote:
>> How do you know that [1,2] is a list that must contain nothing but
>> integers? By extension, it's also a list that must contain positive
>> integers less than three, so adding [5] violates that. And [] is a
>> list that must contain nothing, ergo it can't be added to, although
>> (since it contains nothing) it can be added to anything.
>
> 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
>

First, does Haskell allow this?

? [1,2,'foo'] ++ [3,4,'bar']

If not, then find some other form of the expression that has the same
point, and substitute in for the below. And then: which of these is
permitted?

? [1,2] ++ [3,4,'bar']
? [1,2,'foo'] ++ [3,4]
? [] ++ [3,4,'bar']
? [1,2,'foo'] ++ []
? ([1,2,'foo'] ++ []) ++ [3,4,'bar']
? [1,2,'foo'] ++ ([] ++ [3,4,'bar'])

If it's okay to have heterogeneous lists, how do you tell it that your
[1,2] is actually going to get strings in it later, and that it's okay
to combine it with one that has strings?

With Pike, that's all based on the variable type. (There is type
inference; the type of an array containing just 3 and 4 is
"array(int(3..4))", but it's acceptable to add that to an array
containing the string "asdf", which itself has type
"array(string(97..115))" - the combination would be "array(int(3..4) |
string(97..115))", which gets a bit wordy.) I can't assign an
array(string) to a variable that's been declared as taking array(int).
But I can assign an array(int) to a variable declared as accepting
array(int|string), and then I can append a string to it, because
that's legal based on the destination.

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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