lens-3.9.2: Lenses, Folds and Traversals

Portabilitynon-portable
Stabilityprovisional
MaintainerEdward Kmett <ekmett@gmail.com>
Safe HaskellSafe-Inferred

Control.Lens.Internal.Getter

Contents

Description

 

Synopsis

Internal Classes

class (Contravariant f, Functor f) => Gettable f Source

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

Instances

Getters

coerce :: (Contravariant f, Functor f) => f a -> f bSource

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

newtype Accessor r a Source

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.

Constructors

Accessor 

Fields

runAccessor :: r
 

Instances