Composing Optionals across a Morphic ADT

SeatOptional.ts

import { pipe } from 'fp-ts/lib/pipeable'
import * as L from 'monocle-ts/lib/Lens'
import * as Op from 'monocle-ts/lib/Optional'
import { makeADT, ofType, ADTType } from '@morphic-ts/adt'

interface Bicycle {
  type: 'Bicycle'
  color: string
}

interface Motorbike {
  type: 'Motorbike'
  seats: number
}

interface Car {
  type: 'Car'
  kind: 'electric' | 'fuel' | 'gaz'
  attributes: {
    power: number
    seats: number
  }
}

const Vehicle = makeADT('type')({
  Car: ofType<Car>(),
  Motorbike: ofType<Motorbike>(),
  Bicycle: ofType<Bicycle>()
})
type Vehicle = ADTType<typeof Vehicle>

const fromMotorbike = pipe(
  L.id<Motorbike>(),
  L.prop('seats'),
  L.asOptional,
)

const fromCar = pipe(
  L.id<Car>(),
  L.prop('attributes'),
  L.prop('seats'),
  L.asOptional,
)

const seatOptional: Op.Optional<Vehicle, number> = {
  getOption: Vehicle.match({
    Motorbike: fromMotorbike.getOption,
    Car: fromCar.getOption,
  }, _ => O.none),
  set: (a) => Vehicle.transform({
    Motorbike: fromMotorbike.set(a),
    Car: fromCar.set(a),
  }),
};