[Haskell-cafe] ANN: To Kata Haskellen Evangelion

Joachim Durchholz jo at durchholz.org
Wed Jul 31 05:21:46 UTC 2019

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.


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