generic-lens

Automatically make lenses from data structures implementing Generic

Example Usage (in GHCi)

> :set -XDeriveGeneric -XStandaloneDeriving -XFlexibleContexts -XFlexibleInstances
> import Control.Lens.Generic
> import Control.Monad.Identity
> import GHC.Generics
> import Control.Lens
> data Employee f = Employee (f String) (f Int) deriving Generic
> let Employee (LensFor name) (LensFor age) = lenses

Now you can do things like:

> let x = Employee (return "Frank") (return 2) :: Employee Identity
> runIdentity (x ^. name)
"Frank"
> let y = x & name .~ return "Bob"
> runIdentity (y ^. name)
"Bob"

You can also define the lenses at the top of your module as expected

Employee (LensFor name) (LensFor age) = lenses

The generated lenses have the correct polymorphic van Laarhoven type:

> :type name
name
  :: Functor f =>
     (t String -> f (t String)) -> Employee t -> f (Employee t)