block3.ts

// The `reducer` defines `transitions` for a given `state`
// and `event` (aka `action`) to the next `state`
const reducer = State.match({
  FetchingDimensions: () =>
    Action.match({
      FetchedDimensions: ({ dimensions }) =>
        checkDimensionsValid(dimensions)
          ? State.Uploading()
          : State.Invalid()
    })
});