Copyright	(C) 2020 Csongor Kiss
License	BSD3
Maintainer	Csongor Kiss <kiss.csongor.kiss@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	None
Language	Haskell2010

Data.Generics.Product.Subtype

Contents

Lenses

Description

Structural subtype relationships between product types.

Synopsis

class Subtype sup sub where
- super :: Lens sub sub sup sup
- upcast :: sub -> sup
- smash :: sup -> sub -> sub

Lenses

Running example:

>>> :set -XTypeApplications
>>> :set -XDataKinds
>>> :set -XDeriveGeneric
>>> :set -XDuplicateRecordFields
>>> import GHC.Generics
>>> :m +Data.Generics.Internal.VL.Lens
>>> :{
data Human = Human
  { name    :: String
  , age     :: Int
  , address :: String
  }
  deriving (Generic, Show)
data Animal = Animal
  { name    :: String
  , age     :: Int
  }
  deriving (Generic, Show)
human :: Human
human = Human "Tunyasz" 50 "London"
:}

class Subtype sup sub where Source #

Structural subtype relationship

sub is a (structural) subtype of sup , if its fields are a subset of those of sup .

Minimal complete definition

super | smash , upcast

Methods

super :: Lens sub sub sup sup Source #

Structural subtype lens. Given a subtype relationship sub :< sup , we can focus on the sub structure of sup .

>>> human ^. super @Animal
Animal {name = "Tunyasz", age = 50}

>>> set (super @Animal) (Animal "dog" 10) human
Human {name = "dog", age = 10, address = "London"}

upcast :: sub -> sup Source #

Cast the more specific subtype to the more general supertype

>>> upcast human :: Animal
Animal {name = "Tunyasz", age = 50}

>>> upcast (upcast human :: Animal) :: Human
...
... The type 'Animal' is not a subtype of 'Human'.
... The following fields are missing from 'Animal':
... address
...

smash :: sup -> sub -> sub Source #

Plug a smaller structure into a larger one

>>> smash (Animal "dog" 10) human
Human {name = "dog", age = 10, address = "London"}

Instances

Instances details

Subtype a Void Source #	See Note [Uncluttering type signatures] >>> :t +d super super :: (Subtype sup sub, Functor f) => (sup -> f sup) -> sub -> f sub
Instance details Defined in Data.Generics.Product.Subtype Methods super :: Lens Void Void a a Source # upcast :: Void -> a Source # smash :: a -> Void -> Void Source #
Subtype a a Source #
Instance details Defined in Data.Generics.Product.Subtype Methods super :: Lens a a a a Source # upcast :: a -> a Source # smash :: a -> a -> a Source #
Context a b => Subtype b a Source #
Instance details Defined in Data.Generics.Product.Subtype Methods super :: Lens a a b b Source # upcast :: a -> b Source # smash :: b -> a -> a Source #
Subtype Void a Source #	See Note [Uncluttering type signatures] >>> :t +d super `Int super` Int :: (Subtype Int sub, Functor f) => (Int -> f Int) -> sub -> f sub
Instance details Defined in Data.Generics.Product.Subtype Methods super :: Lens a a Void Void Source # upcast :: a -> Void Source # smash :: Void -> a -> a Source #