Internal Classes

This class is provided mostly for backwards compatibility with lens 3.8, but it can also shorten type signatures.

This Generalizes Const so we can apply simple Applicative transformations to it and so we can get nicer error messages.

A Functor you can coerce ignores its argument, which it carries solely as a phantom type parameter.

By the Functor and Contravariant laws, an instance of Gettable will necessarily satisfy:

id = fmap f = coerce = contramap g

The mempty equivalent for a Gettable Applicative Functor.

Used instead of Const to report

No instance for (Settable Accessor)

when the user attempts to misuse a Setter as a Getter, rather than a monolithic unification error.