[Haskell-cafe] Representation of lenses

[Tom Ellis]

On Tue, Jan 27, 2015 at 05:50:44PM +0000, David Turner wrote:
> Notice that Const s is not an Applicative (e.g. pure :: () -> Const
> Void () doesn't exist) which is why (forall f. Applicative f => (s ->
> f s) -> a -> f a) proscribes getting your hands on the getter.

Right, unless `s` is a `Monoid` in which case you can "get" out of a
`Traversal` by combining all the targets :)