[Haskell-cafe] Foldable for (,)

amindfv at gmail.com amindfv at gmail.com
Thu May 4 20:52:18 UTC 2017

> El 4 may 2017, a las 14:20, Olaf Klinke <olf at aatal-apotheke.de> escribió:


>  Most mathematicians are happy to use the Axiom of Choice, knowing that accepting it leads to things like the Banach-Tarski Paradox. Then there are constructivists who deny the existence of non-measurable sets (because you need the Axiom of Choice to prove their existence), and the Banach-Tarski Paradox goes away. By this analogy, the Foldable instance of ((,) a) is the Banach-Tarski paradox which we accept and avoid to obtain other nice things we need. 

This to me is the center of the conversation: we're choosing whether we need the instances badly enough that we tolerate some, ahem, bad behavior. Can you provide specific code examples where you (or others) truly needed those instances to get something done?


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