Deriving in that way is more of a question of which breaks more code, I
think. Or avoiding breaking code vs. purity arguments, which worry me at
least somewhat less because that horse left the stable with Haskell 98
twisting Monad out of shape (granting we're trying to fix at least part of
it now), if not earlier. And, well, it's a computer language. "Proper
purity" not gonna happen in general, unless the result is a useless toy.
But Haskell strives to be usable.
On Tue, Jul 30, 2019 at 3:31 PM Olaf Klinke
Isn't the Eq vs Ord problem similar to all sub-classes, e.g. Applicative vs. Monad, Semigroup vs. Monoid, Foldable vs. Traversable? What is the recommended way of coding? The Traversable module for example has default implementations of fmap and foldMap, as Functor and Foldable are superclasses. This suggests it is okay to define the subclass method first and derive the superclass methods from them. But arguments have been put up against this practice in particular cases, e.g. for AMP [1].
Olaf
[1] https://mail.haskell.org/pipermail/haskell-cafe/2019-July/131259.html
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