Are we even sure this law isn't already guaranteed by parametricity and perhaps the existing laws of the other type classes involved? I for one can't think of a pointed traversable which doesn't already obey this law.
There was a lot of discussion about separating "pure" from Applicative and putting it into a Pointed class. If I remember correctly, the main counter argument was that 'pure' alone does not satisfy interesting laws. There are only such laws in connection with the Applicative class.
Now, in some situations I liked to have a generalized unfoldr. I can build this from "pure" and "sequenceA" using the State monad:
unfoldr :: (Pointed t, Traversable t) => (s -> (a, s)) -> s -> t a
unfoldr = evalState . sequenceA . pure . state
One could state a law like:
traverse f (pure a) == traverse id (pure (f a))
Would this justify to move "pure" into a new Pointed class?
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