Data.Generics.Sum.Constructors

Derive constructor-name-based prisms generically.

Prisms

class AsConstructor ctor a s | s ctor -> a where

Sums that have a constructor with a given name.

Methods

_Ctor :: Prism' s a

A prism that projects a named constructor from a sum. Compatible with the lens package's Prism type.

>>> dog ^? _Ctor @"Dog"
Just (MkDog {name = "Shep", age = 3})

>>> dog ^? _Ctor @"Cat"
Nothing

>>> cat ^? _Ctor @"Cat"
Just ("Mog", 5)

>>> _Ctor @"Cat" # ("Garfield", 6) :: Animal
Cat ("Garfield", 6)

Instances

(Generic s, ErrorUnless ctor s (HasCtorP ctor (Rep s)), GAsConstructor ctor (Rep s) a) => AsConstructor ctor a s

Methods

_Ctor :: Prism' s a