Modulegeneric-lens-2.2.2.0Haskell2010

Data.Generics.Product.Subtype

Structural subtype relationships between product types.

1 class

Packagegeneric-lens-2.2.2.0
Exports1
LanguageHaskell2010
LicenceBSD-3-Clause
SourceSubtype.hs

Lenses

1 declaration

Running example:

Example7 expressions

>>> :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 :: Humanhuman = Human "Tunyasz" 50 "London":}

classclass Subtype sup sub where

Structural subtype relationship

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

Methods

super :: Lens sub sub sup sup
Structural subtype lens. Given a subtype relationship sub :< sup, we can focus on the sub structure of sup.
Example1 expression
```
>>> human ^. super @AnimalAnimal {name = "Tunyasz", age = 50}
```
Example1 expression
```
>>> set (super @Animal) (Animal "dog" 10) humanHuman {name = "dog", age = 10, address = "London"}
```

upcast :: sub -> sup

Cast the more specific subtype to the more general supertype

Example1 expression

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

Example1 expression

>>> 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

Plug a smaller structure into a larger one

Example1 expression

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

Instances4Subtype

Subtype Void aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Subtype
Uncluttering type signatures (see Void)
Example1 expression
```
>>> :t +d super @Intsuper @Int  :: (Subtype Int sub, Functor f) => (Int -> f Int) -> sub -> f sub
```
Subtype a VoidDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Subtype
Uncluttering type signatures (see Void)
Example1 expression
```
>>> :t +d supersuper  :: (Subtype sup sub, Functor f) => (sup -> f sup) -> sub -> f sub
```
Subtype a aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Subtype
Context a b => Subtype b aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Subtype