[Haskell-cafe] Partial instance of a class

[Tom Ellis]

On Tue, Feb 27, 2018 at 11:21:51AM +0000, Tom Ellis wrote:
> NB that if you implement Category and Profunctor then you automatically get
> arr (\f -> lmap f id).

Or perhaps put more simply, you have no hope of making something an Arrow if
you can't make it a Functor, but if you *do* have Functor and Category then
you automatically get

    arr f = fmap f id

Tom