An L.append to a nested L.found-array fails about partial.lenses

[polytypic]

    const change = R.compose(
        L.set(newRoomLens(7357), {roomType: 'DOUBLE', ratePlan: 'RAC'}),
        L.set(hotelLens(7357), {id: 7357, name: 'Hotel Opera'})
    )

What this does is that the latter operation L.set(hotelLens(...), {...}) replaces the whole object. So, what you get is an idempotent operation: no matter how many times it is applied, the result is the same as from the first application.

Continued shortly...

[polytypic]

function hotelLens(id) {
  return L.compose(
    L.prop('bookingOrder'),
    L.prop('hotels'),
    L.find(R.whereEq({id})),
    L.defaults({id})
  )
}

function nameLens(hotelId) {
  return L.compose(hotelLens(hotelId), L.prop("name"))
}

function newRoomLens(hotelId) {
  return L.compose(
    hotelLens(hotelId),
    L.prop('rooms'),
    L.append
  )
}

const change = R.compose(
  L.set(newRoomLens(7357), {roomType: 'DOUBLE', ratePlan: 'RAC'}),
  L.set(nameLens(7357), 'Hotel Opera')
)

const state = {bookingOrder: {hotels: []}}

change(change(state))

Above is one way to avoid the problem.

Setting the hotel name and adding rooms in a composed function seems a bit suspect. I would assume that one would want to first set the hotel name and then perhaps add multiple rooms.

Note that there is also a gitter channel where lens questions are certainly on topic.

[ikr]

Ah, I see now. Thanks a lot for your detailed answer! I'll probably use the gitter channel quite a bit :)