Modulegeneric-lens-2.2.2.0Haskell2010

Data.Generics.Product.Positions

Derive positional product type getters and setters generically.

4 classes
2 values

Packagegeneric-lens-2.2.2.0
Exports6
LanguageHaskell2010
LicenceBSD-3-Clause
SourcePositions.hs

Lenses

6 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 = Human  { name    :: String  , age     :: Int  , address :: String  }  deriving (Generic, Show)human :: Humanhuman = Human "Tunyasz" 50 "London":}

classclass HasPosition (i :: Nat) s t a b | s i -> a, t i -> b, s i b -> t, t i a -> s where

Records that have a field at a given position.

Methods

position :: Lens s t a b

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

Example2 expressions

>>> human ^. position @1"Tunyasz">>> human & position @3 .~ "Berlin"Human {name = "Tunyasz", age = 50, address = "Berlin"}

Type errors

Example1 expression

>>> human & position @4 .~ "Berlin"...... The type Human does not contain a field at position 4...

Instances2HasPosition

(Context i s t a b, HasPosition0 i s t a b) => HasPosition i s t a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions
HasPosition f (Void1 a) (Void1 b) a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions
Uncluttering type signatures (see Void)
Example1 expression
```
>>> :t +d positionposition  :: (HasPosition i s t a b, Functor f) => (a -> f b) -> s -> f t
```

classclass HasPosition' (i :: Nat) s a | s i -> a where

Records that have a field at a given position.

The difference between HasPosition and HasPosition_ is similar to the one between HasField and HasField_. See HasField_.

Methods

position' :: Lens s s a a

Instances1HasPosition'

Context' i s a => HasPosition' i s aDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions

classclass HasPosition_ (i :: Nat) s t a b where

Methods

position_ :: Lens s t a b

Instances2HasPosition_

(Context_ i s t a b, HasPosition0 i s t a b) => HasPosition_ i s t a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions
HasPosition_ f (Void1 a) (Void1 b) a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions

classclass HasPosition0 (i :: Nat) s t a b where

Records that have a field at a given position.

This class gives the minimal constraints needed to define this lens. For common uses, see HasPosition.

Methods

position0 :: Lens s t a b

Instances1HasPosition0

Context0 i s t a b => HasPosition0 i s t a bDefined in generic-lens-2.2.2.0 · Data.Generics.Product.Positions

valuegetPosition :: HasPosition' i s a => s -> a

Example1 expression

>>> getPosition @2 human50

valuesetPosition :: HasPosition' i s a => a -> s -> s

Example1 expression

>>> setPosition @2 60 humanHuman {name = "Tunyasz", age = 60, address = "London"}