.. (C) 2025 Albert Mietus. Part of CCastle project

.. _CastleLib-MainComponent:

==================
The Main Component
==================

.. sidebar:: Main

   .. note The code-tabs use ReasonML , but it is Castle-code!!
   .. tabs::

      .. code-tab:: ReasonML Main

         component Main : Component {
            port std<bidir>:std; // Or spilt it?
         }

      .. code-tab:: ReasonML Protocols

         protocol std : EventProtocol {
            invoke();
            stdin(line:txt);  //Todo
            stdout(line:txt); //ToDo
            stderr(line:txt); //ToDo
         }

      .. tab:: Syntax notes

         As the Castle syntax isn't fully stable, a few notes:

         - Parameters are in ``name:type`` order, which may change.


The ``Main`` Component defines a simple Component, which has the *standard ports**\ [#std_ports]_ added. It is always used as base-component.
|BR|
In this way, “main components”[#mainComp]_ have the ``invoke`` event, known by the Command Pattern.

Castle programmers can easily implement such a “main component”, by implementing that event-handler, and run it by calling ``invoke()`` on an elements. Using the
the ``@impliciet`` rewriter makes it even more simple, as can be seen in the demo below.

.. tabs::

   .. code-tab:: ReasonML Demo Component

      @impliciet(Main)                   ///GAM: This `rewriter` auto-generates the interface -- based on Main
      implement Demo {

      invoke() on self.std {
         // ....
      }

   .. code-tab:: ReasonML Run it

      Demo().std.invoke()

----------

.. caution::

   At the moment there is no design for bidir-ports. The idea is that a ‘bidir (event) port’ is both an input and an output port combined.

   So, the Castle programmer can (or must?) write an event-handler for every event in the protocol, and sent all event out over that port.


----------

.. rubric:: Footnotes

.. [#std_ports]
   For now, it is one **bidir** (bidirectional) port with a protocol that supports input (& control) and output. This might change to separate ports.

.. [#mainComp]
   Or, strictly speaking, components that inherit from ``Main``.