Combinators

Combinators cover the common optics you do not want to rebuild by hand.

guard

Creates a prism from a TypeScript type guard.

import { guard } from '@fuiste/optics'

type Circle = { type: 'circle'; radius: number }
type Square = { type: 'square'; side: number }
type Shape = Circle | Square

const circle = guard<Shape, Circle>((shape): shape is Circle => shape.type === 'circle')

circle.get({ type: 'circle', radius: 5 })
// { type: 'circle', radius: 5 }

circle.get({ type: 'square', side: 4 })
// undefined

at

Creates a prism for a record key.

import { at } from '@fuiste/optics'

const authorization = at<string>('Authorization')

authorization.get({ Authorization: 'Bearer token' })
// 'Bearer token'

authorization.set('Bearer next')({})
// { Authorization: 'Bearer next' }

index

Creates a prism for a single array element.

import { index } from '@fuiste/optics'

const second = index<number>(1)

second.get([10, 20, 30])
// 20

second.set(99)([10, 20, 30])
// [10, 99, 30]

each

Creates a traversal for every element in an array.

import { each } from '@fuiste/optics'

const numbers = each<number>()

numbers.modify((value) => value * 2)([1, 2, 3])
// [2, 4, 6]