=========================
Reactive MVU Architecture
=========================

Fable.Reaction is very similar to `Elm <http://elm-lang.org/>`_ and
`Elmish <https://elmish.github.io/>`_ in regards to the `MVU
architecture <https://guide.elm-lang.org/architecture/>`_. But when using
Fable.Reaction, we do not need any commands (``Cmd``) or subscriptions
with Elmish. Instead we use a `ReactiveX <http://reactivex.io/>`_
(AsyncRx) style query that transforms the stream of messages (``Msg``).

.. image:: /_static/R-MVU.png
    :width: 550px

* **Model**, application state as immutable data

* **View**, a pure function that takes the model to produce the output
  view (HTML elements)

* **Message**, a data event that represents a change. Messages are
  generated by the view, or they may be generated by a stream,
  e.g. timer or initial message events.

* **Update**, a pure function that produces a new model based on a
  received message and the previous model

In addition to the normal MVU architecture, Fable.Reaction also have a
stream that transforms the "stream" of messages going from the view to
the update function.

* **Stream**, a function that takes the current model and the message
  stream and produces a new (transformed) message stream. Note that
  this also replaces the need for Elm(ish) commands (Cmd) since the
  stream is free to produce any messages (out of thin air), transform,
  filter, time-shift messages or combine side-effects such as web
  requests (fetch) etc.