Data.Generics.Sum

Magic sum operations using Generics

These classes need not be instantiated manually, as GHC can automatically prove valid instances via Generics. Only the Generic class needs to be derived (see examples).

Prisms

class AsAny sel a s | s sel k -> a where

Sums that have generic prisms.

Methods

_As :: Prism' s a

A prism that projects a sum as identified by some selector. Currently supported selectors are constructor names and unique types. Compatible with the lens package's Prism type.

>>> dog ^? _As @"Dog"
Just (MkDog {name = "Shep", age = 3})
>>> dog ^? _As @Dog
Just (MkDog {name = "Shep", age = 3})
>>> dog ^? _As @"Cat"
Nothing
>>> cat ^? _As @"Cat"
Just ("Mog", 5)
>>> _As @"Cat" # ("Garfield", 6) :: Animal
Cat ("Garfield", 6)
>>> duck ^? _As @Age
Just 2

Instances

AsConstructor ctor a s => AsAny Symbol ctor a s

Methods

_As :: Prism' s s

AsType a s => AsAny * a a s

Methods

_As :: Prism' s s

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

class AsType a s where

Sums that have a constructor with a field of the given type.

Methods

_Typed :: Prism' s a

A prism that projects a constructor uniquely identifiable by the type of its field. Compatible with the lens package's Prism type.

>>> dog ^? _Typed @Dog
Just (MkDog {name = "Shep", age = 3})
>>> dog ^? _Typed @Cat
Nothing
>>> duck ^? _Typed @Age
Just 2

Instances

(Generic s, ErrorUnlessOne a s (CountPartialType a (Rep s)), GAsType (Rep s) a) => AsType a s

Methods

_Typed :: Prism' s a