[Haskell-cafe] ANN: To Kata Haskellen Evangelion

Brandon Allbery allbery.b at gmail.com
Wed Jul 31 10:15:37 UTC 2019

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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