Modulegeneric-lens-2.2.2.0Haskell2010

Data.Generics.Product.Fields

Derive record field getters and setters generically.

3 classes
2 values

Packagegeneric-lens-2.2.2.0
Exports5
LanguageHaskell2010
LicenceBSD-3-Clause
SourceFields.hs

Lenses

5 declarations

Running example:

Example9 expressions

>>> :set -XTypeApplications>>> :set -XDataKinds>>> :set -XDeriveGeneric>>> :set -XGADTs>>> :set -XFlexibleContexts>>> import GHC.Generics>>> :m +Data.Generics.Internal.VL.Lens>>> :m +Data.Function>>> :{data Human a  = Human    { name    :: String    , age     :: Int    , address :: String    , other   :: a    }  | HumanNoAddress    { name    :: String    , age     :: Int    , other   :: a    }  deriving (Generic, Show)human :: Human Boolhuman = Human { name = "Tunyasz", age = 50, address = "London", other = False }:}

classclass HasField (field :: Symbol) s t a b | s field -> a, t field -> b, s field b -> t, t field a -> s where

Records that have a field with a given name.

Methods

field :: Lens s t a b

A lens that focuses on a field with a given name. Compatible with the lens package's Control.Lens.Lens type.

Example1 expression

>>> human ^. field @"age"50

Type changing

Example1 expression

>>> :t humanhuman :: Human Bool

Example1 expression

>>> :t human & field @"other" .~ (42 :: Int)human & field @"other" .~ (42 :: Int) :: Human Int

Example1 expression

>>> human & field @"other" .~ 42Human {name = "Tunyasz", age = 50, address = "London", other = 42}

Type errors

Example1 expression

>>> human & field @"weight" .~ 42...... The type Human Bool does not contain a field named 'weight'....

Example1 expression

>>> human & field @"address" .~ ""...... Not all constructors of the type Human Bool... contain a field named 'address'.... The offending constructors are:... HumanNoAddress...

Instances2HasField

(Context field s t a b, HasField0 field s t a b) => HasField field s t a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields
HasField f (Void1 a) (Void1 b) a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields
Uncluttering type signatures (see Void)
Example1 expression
```
>>> :t +d fieldfield  :: (HasField field s t a b, Functor f) => (a -> f b) -> s -> f t
```

classclass HasField' (field :: Symbol) s a | s field -> a where

Methods

field' :: Lens s s a a

Instances2HasField'

Context' field s a => HasField' field s aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields
HasField' f (Void1 a) aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields

classclass HasField_ (field :: Symbol) s t a b where

Records that have a field with a given name.

This is meant to be more general than HasField, but that is not quite the case due to the lack of functional dependencies.

The types s and t must be applications of the same type constructor. In contrast, HasField also requires the parameters of that type constructor to have representational roles.

One use case of HasField_ over HasField is for records defined with data instance.

Methods

field_ :: Lens s t a b

Instances2HasField_

(Context_ field s t a b, HasField0 field s t a b) => HasField_ field s t a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields
HasField_ f (Void1 a) (Void1 b) a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Fields

valuegetField :: HasField' f s a => s -> a

Example1 expression

>>> getField @"age" human50

valuesetField :: HasField' f s a => a -> s -> s

Example1 expression

>>> setField @"age" 60 humanHuman {name = "Tunyasz", age = 60, address = "London", other = False}