Control.Lens.Internal.Getter

Internal Classes

Getters

class Functor f => Gettable f where

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

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

To ensure this, an instance of Gettable is required to satisfy:

id = fmap f = coerce

Which is equivalent to making a Gettable f an "anyvariant" Functor.

Methods

coerce :: f a -> f b

Replace the phantom type argument.

Instances

Gettable (Const r)

Gettable f => Gettable (Backwards f)

Gettable (Accessor r)

Gettable f => Gettable (Indexing64 f)

Gettable f => Gettable (Indexing f)

(Functor f, Gettable g) => Gettable (Compose f g)

Gettable (Effect m r)

(Profunctor p, Gettable g) => Gettable (PretextT p g a b)

(Profunctor p, Gettable g) => Gettable (BazaarT p g a b)

Gettable f => Gettable (TakingWhile p f a b)

Gettable (EffectRWS w st m s)

noEffect :: (Applicative f, Gettable f) => f a

The mempty equivalent for a Gettable Applicative Functor.

newtype Accessor r a

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

Effective Identity r (Accessor r)

Functor (Accessor r)

Monoid r => Applicative (Accessor r)

Semigroup r => Apply (Accessor r)

Gettable (Accessor r)