Data.Generics.Product

Magic product 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).

Magic lens

class HasFieldAt index a s | s index -> a where

Types that have a field at given position.

Minimal complete definition

itemAt

Methods

itemAt :: Lens' s a

Lens focusing on a field at a given index. Compatible with the lens package.

>>> human & itemAt @1 .~ "Tamas"
Human "Tamas" 50 "London"

Instances

(Generic s, (~) Bool (ContainsAt BaseIndex index (Rep s)) True, GHasFieldAt BaseIndex index (Rep s) a) => HasFieldAt index a s

Instances are generated on the fly for all types that have the required positional field.

Methods

itemAt :: Lens' s a

Getter and setter

getFieldAt :: forall index a s. HasFieldAt index a s => s -> a

Get positional field

>>> getFieldAt @1 human
"Tunyasz"

setFieldAt :: forall index a s. HasFieldAt index a s => a -> s -> s

Set positional field

>>> setFieldAt @2 (setField @1 "Tamas" human) 30
Human "Tamas" 30 "London"