Monocle.Lens

A Lens is a functional concept which solves a very common problem: how to easily update a complex immutable structure, for this purpose Lens acts as a zoom into a record.

Definition

type alias Lens a b =

{ get : a -> b

, set : b -> a -> a

}

In order to create Lens we need to suply 2 functions: set and get

Example

addressStreetNameLens : Lens Address String
addressStreetNameLens =
    let
        get a = a.streetName


        set sn a = { a | streetName = sn }
    in
        Lens get set


placeAddressLens : Lens Place Address
placeAddressLens =
    let
        get p = p.address


        set a p = { p | address = a }
    in
        Lens get set


placeStreetName: Lens Place String
placeStreetName = placeAddressLens `compose` addressStreetNameLens

Derived methods

compose : Lens a b -> Lens b c -> Lens a c

Composes Lens a b with Lens b c and returns Lens a c

modify : Lens a b -> (b -> b) -> a -> a

Modifies given function (b -> b) to be (a -> a) using Lens a b

addressStreetNameLens = Lens Address String
fx streetName = String.reverse streeName
fx2 = Lens.modify addressStreetNameLens fx
fx2 {streetName="abcdef"} == {streetName="fedcba"}

zip : Lens a c -> Lens b d -> Lens ( a, b ) ( c, d )

Zips Lens a c with Lens b d to form Lens ( a, b ) ( c, d )

Conversion

fromIso : Iso a b -> Lens a b

Casts Iso a b to Lens a b

arturopala/elm-monocle/1.1.0

Monocle.Lens

Definition

Example

Derived methods

Conversion

Modules