[Haskell-cafe] ANN: To Kata Haskellen Evangelion

[Cosmia Fu]

I am not sure what you are talking about, but in the scope of Haskell, even
functions or values involving IO are pure if you do not count the unsafeXXX.

On Wed, Jul 31, 2019 at 7:15 PM Brandon Allbery <allbery.b at gmail.com> wrote:

> I didn't mean purity in the Haskell sense, but the more general technical
> sense the original message seemed to me to be reaching for. Purity in the
> Haskell sense is indeed a more limited question. But languages that are
> useful int he real world need to make tradeoffs, and even Haskell's version
> of purity includes such (IO is in many ways a wart, but there's going to be
> a wart *somewhere*).
>
> On Wed, Jul 31, 2019 at 1:22 AM Joachim Durchholz <jo at durchholz.org>
> wrote:
>
>> Am 30.07.19 um 21:35 schrieb Brandon Allbery:
>> > And, well, it's a computer language. "Proper
>> > purity" not gonna happen in general, unless the result is a useless
>> toy.
>>
>> I do not think that the limitations from Haskell's design choices can be
>> generalized to all programming languages in this way.
>>
>> Purity (i.e. no side effects) is easy in strict languages, for example.
>>
>> In a nonstrict language, you'd need a proof of termination to have
>> purity (nontermination is impure).
>>
>> Another approach would be to control impurities. Based on the
>> observation that all code is impure, such as heating the CPU, taking
>> time, increasing CPU counters, and we do not care about these
>> impurities. One could design a language where one could e.g. write a
>> completely impure logger, call it from pure code, and statically
>> determine that these impurities do not affect the pure code.
>>
>> While I think that your pessimism is justified for Haskell where pretty
>> fundamental design choices would have to be reverted, I conclude it is
>> not necessarily justified in the generality stated.
>>
>> Regards,
>> Jo
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>
>
>
> --
> brandon s allbery kf8nh
> allbery.b at gmail.com
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