Iso

An Iso<S, A> is a total invertible mapping between two representations.

type Iso<S, A> = {
  readonly _tag: 'iso'
  readonly to: (s: S) => A
  readonly from: (a: A) => S
}

Create An Iso

import { Iso } from '@fuiste/optics'

const numberString = Iso<number, string>({
  to: (value) => `${value}`,
  from: (value) => Number.parseInt(value, 10),
})

numberString.to(42)
// '42'

numberString.from('7')
// 7

Compose With A Lens

import { Lens, Iso, compose } from '@fuiste/optics'

type Model = { count: number }

const count = Lens<Model>().prop('count')
const numberString = Iso<number, string>({
  to: (value) => `${value}`,
  from: (value) => Number.parseInt(value, 10),
})

const countAsString = compose(count, numberString)

countAsString.get({ count: 7 })
// '7'

countAsString.set('10')({ count: 7 })
// { count: 10 }

Notes

• to and from should be inverses.
• Iso is transparent in most composition: Lens ∘ Iso is still a Lens.
• Iso ∘ Iso is an Iso.