[Haskell-cafe] Are bottoms ever natural?
(IIIT) Siddharth Bhat
siddharth.bhat at research.iiit.ac.in
Tue Dec 19 07:20:07 UTC 2017
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?
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?
>> Sending this from my phone, please excuse any typos!
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> brandon s allbery kf8nh sine nomine
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
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Sending this from my phone, please excuse any typos!
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