Got into yet another argument that Haskell's type classes were superior to Scala's because Haskell has global instance uniqueness. Problem being, as far as I can tell, this is true in theory (by specifications) but not in practice (by implementation): https://nrinaudo.github.io/typeclasses/haskell.html …
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Fair enough - what did I miss in my (nasty) bit of code? Doesn't it expose exactly the fact that global uniqueness is not guaranteed by ghc? Who's got the bigger type class implementation is another debate entirely and not at all the point I was making, sorry if it was unclear
The argument is practical Write Haskell; never use orphan instances. This is achievable with little/no penalty Write Scala; never use orphan instances. With this commitment, it's difficult & there's no sweet spot Scala does not have type-classes in any general practical sense
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That is entirely besides the point though. My point is: GHC doesn't enforce global instance uniqueness. This is demonstrably true, but exhibiting a program in which global instance uniquess is violated. Whether or not it's easy to avoid is another discussion
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I will agree that a well disciplined team with 0 external dependencies will have no such problem in Haskell, but is almost guaranteed to have them in Scala. I'm not aware of a mechanism by which you can guarantee that your Haskell dependencies don't do what I did though.
End of conversation
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The separate discussion that you're answering to is interesting though. I'd like to know how you define a type class, and in which way that definition invalidates Scala's encoding of them. This is neither a challenge nor sarcasm. I'm genuinely interested.
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It's a rabbit hole! Happy to go there though.
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