[Haskell-cafe] Are bottoms ever natural?

[(IIIT) Siddharth Bhat]

Also, I'm sorry if the tone of the email is hostile, I don't mean it that
way :) I just want to start a discussion about compiler and language design
around lazy languages that permit bottom as an inhabitant.

On Tue 19 Dec, 2017, 08:20 (IIIT) Siddharth Bhat, <
siddharth.bhat at research.iiit.ac.in> wrote:

> Is that really true, though?
> Usually when you have an infinite loop, you have progress of some sort.
> Infinite loops with no side effects can be removed from the program
> according to the C standard, for example. So, in general, we should allow
> programmers to express termination / progress, right? At that point, no
> computation ever "bottoms out"?
>
> Shouldn't a hypothetical purely functional programming language better
> control this (by eg. Forcing totality?) It seems like we lose much of the
> benefits of purity by muddying the waters with divergence.
>
> From an optimising compiler perspective, Haskell is on some weird
> lose-lose space, where you lose out on traditional compiler techniques that
> work on strict code, but it also does not allow the awesome stuff you could
> do with "pure" computation because bottom lurks everywhere.
>
> What neat optimisations can be done on Haskell that can't be done in a
> traditional imperative language? I genuinely want to know.
>
> What are your thoughts on this?
>
> Cheers
>
>
> Siddharth
>
> On Tue 19 Dec, 2017, 08:09 Brandon Allbery, <allbery.b at gmail.com> wrote:
>
>> Define "natural".
>>
>> You might want to look into the concept of Turing completeness. One could
>> define a subset of Haskell in which bottoms cannot occur... but it turns
>> out there's a lot of useful things you can't do in such a language. (In
>> strict languages, these often are expressed as infinite loops of one kind
>> or another. Note also that any dependency on external input is an infinite
>> loop from the perspective of the language, since it can only be broken by
>> the external entity providing the input.)
>>
>> On Tue, Dec 19, 2017 at 1:47 AM, (IIIT) Siddharth Bhat <
>> siddharth.bhat at research.iiit.ac.in> wrote:
>>
>>> I've been thinking about the issue of purity and speculation lately, and
>>> from what little I have read, it looks like the presence of bottom hiding
>>> inside a lazy value is a huge issue.
>>>
>>> How "natural" is it for bottoms to exist? If one were to change Haskell
>>> and declare that any haskell value can be speculated upon, what
>>> ramifications does this have?
>>>
>>> Is it totally broken? Is it "correct" but makes programming unpleasant?
>>> What's the catch?
>>>
>>> Thanks,
>>> Siddharth
>>> --
>>> Sending this from my phone, please excuse any typos!
>>>
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>>
>>
>>
>> --
>> brandon s allbery kf8nh                               sine nomine
>> associates
>> allbery.b at gmail.com
>> ballbery at sinenomine.net
>> unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
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>
> --
> Sending this from my phone, please excuse any typos!
>
-- 
Sending this from my phone, please excuse any typos!
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