Data.Lens.Injection.Injection4

The fourth injection of a sum type, as a prism. The sum-type dual of Control.Lens.Field4.

Synopsis

classclass Injection4 s t a b | s -> a, t -> b, s b -> t, t a -> s where

Access the fourth constructor of a sum type.

Where Control.Lens._4 is the fourth projection out of a product, _I4 is the fourth injection into a sum.

The default implementation is the prism to the fourth constructor of a Generic type, injection (Proxy :: Proxy 3).

Example3 expressions

>>> data T = C1 | C2 | C3 | C4 Int | C5 deriving (Show, Generic)>>> instance Injection4 T T Int Int>>> C4 1 ^? _I4Just 1

Example1 expression

>>> C5 ^? _I4Nothing

Example1 expression

>>> _I4 # 1 :: TC4 1