Extending a bundle

Bundles are pipeable. Each combinator returns a new bundle and leaves the original unchanged, and its callbacks are typed from the bundle:

const LoggedCounter = Counter.pipe(
  Bundle.rename('LoggedCounter'),
  Bundle.mapUpdate(update => (model, message, args) => {
    console.log(message._tag)
    return update(model, message, args)
  }),
  Bundle.withHelpers({ clear: (model: CounterModel) => ({ model: { ...model, count: 0 } }) }),
)

mapInit, mapView, withView, and withSubscriptions complete the set. mapUpdate layers run outer then inner. mapView wraps the view a bundle has, keeping its inputs; withView gives a bundle a view with inputs of that view's own, which is how a package that only draws (such as foldkit-mixins-form) adds a view to a bundle it did not write.