Lens

Lens: object

Defined in: Core/Lens.ts:24

Type Declaration

andThen

andThen: <A, B>(inner) => <S>(outer) => Lens<S, B>

Composes two Lenses: focuses through the outer, then through the inner. Use in a pipe chain to build up a deep focus step by step.

Type Parameters

A

A

B

B

Parameters

inner

Lens<A, B>

Returns

<S>(outer) => Lens<S, B>

Example

const userCityLens = pipe(
  Lens.from.property<User>()("address"),
  Lens.andThen(Lens.from.property<Address>()("city")),
);

andThenOptional

andThenOptional: <A, B>(inner) => <S>(outer) => Optional<S, B>

Composes a Lens with an Optional, producing an Optional. Use when the next step in the focus is optional (may be absent).

Type Parameters

A

A

B

B

Parameters

inner

Optional<A, B>

Returns

<S>(outer) => Optional<S, B>

Example

const userBioOpt = pipe(
  Lens.from.property<User>()("profile"),
  Lens.andThenOptional(Optional.from.property<Profile>()("bio")),
);

from

from: object

from.accessors

accessors: <S, A>(get, set) => Lens<S, A> = makeAccessors

Constructs a Lens from a getter and a setter.

Type Parameters

S

S

A

A

Parameters

get

(s) => A

set

(a) => (s) => S

Returns

Lens<S, A>

Example

const nameLens = Lens.from.accessors(
  (user: User) => user.name,
  (name) => (user) => ({ ...user, name }),
);

from.property

property: <S>() => <K>(key) => Lens<S, S[K]> = makeProperty

Creates a Lens that focuses on a property of an object. Call with the structure type first, then the key.

Type Parameters

S

S

Returns

<K>(key) => Lens<S, S[K]>

Example

const nameLens = Lens.from.property<User>()("name");

get

get: <S, A>(lens) => (s) => A

Reads the focused value from a structure.

Type Parameters

S

S

A

A

Parameters

lens

Lens<S, A>

Returns

(s) => A

Example

pipe(user, Lens.get(nameLens)); // "Alice"

modify

modify: <S, A>(lens) => (f) => (s) => S

Applies a function to the focused value, returning a new structure.

Type Parameters

S

S

A

A

Parameters

lens

Lens<S, A>

Returns

(f) => (s) => S

Example

pipe(user, Lens.modify(nameLens)(n => n.toUpperCase())); // "ALICE"

set

set: <S, A>(lens) => (a) => (s) => S

Replaces the focused value within a structure, returning a new structure.

Type Parameters

S

S

A

A

Parameters

lens

Lens<S, A>

Returns

(a) => (s) => S

Example

pipe(user, Lens.set(nameLens)("Bob")); // new User with name "Bob"

toOptional

toOptional: <S, A>(lens) => Optional<S, A>

Converts a Lens to an Optional. Every Lens is a valid Optional whose get always returns Some.

Type Parameters

S

S

A

A

Parameters

lens

Lens<S, A>

Returns

Optional<S, A>

Example

pipe(
  Lens.from.property<User>()("address"),
  Lens.toOptional,
  Optional.andThen(Optional.from.property<Address>()("landmark")),
);