Chaining AppCons

One of the principles of the TAO is using fine-grained Application Contexts to provide a programming paradigm grounded in Functional Programming.

Handlers can tell the TAO which Application Context is next after they complete their execution by returning an AppCon to the caller.

Using this mechanism, a System Actor (like a User)'s interaction with our app can trigger a single Application Context which then triggers a multitude of Application Contexts to generate and track the correct behaviors of our application.

This design allows us to use fine-grained Application Context definitions in order to keep our handlers small and focused on a Single Responsibility, offering to allow downstream Application Contexts to react to what the handler has done.

Example Chain

Borrowing and reprinting from our earlier Example AppCon Descriptions:

from TAO to TAO description
{App,Enter,Portal} initial TAO that sets the App in motion (this can be anything you want)
{App,Enter,Portal} ->{App,View,Portal} after entering, we want to show the App's Portal
{App,View,Portal} ->{Space,Find,Portal} visitng the App's initial Portal View triggers a fetch for the items that should be visible
{Space,Find,Portal} ->{Space,List,Portal} with the items, render the list for the User

We see that we want the {App,Enter,Portal} Application Context to trigger the {App,View,Portal} Application Context.

Must use AppCon Constructor

The TAO only reacts to AppCons which are returned from handlers and not any other form of an Application Context or trigram. The TAO will not inspect the return value of a handler other than to determine if it is of AppCon type.

This does allow you to extend the AppCon class if you so desire and returning those will still work. However, it's better to favor Composition over Inheritance so this isn't something you really should consider.

Chaining AppCon in Code

In order for our handler to chain to another AppCon, we need to ensure we are importing both the TAO and AppCon constructor where we plan to do it:

import TAO, { AppCon } from '@tao.js/core';


const TAO, { AppCon } = require('@tao.js/core');

Here is a sample handler that ensures the TAO goes to the {App,View,Portal} Application Context when it is finished:

TAO.addInlineHandler({ t: 'App', a: 'Enter', o: 'Portal' }, (tao, data) => {
  const title = data.title;
  return new AppCon('App', 'View', 'Portal', data);
// OR
TAO.addInlineHandler({ term: 'App', action: 'Enter', orient: 'Portal' }, (tao, data) => {
  const title = data.title;
  return new AppCon('App', 'View', 'Portal', data);

It's as simple as that, yet this mechanism becomes a very powerful force in allowing us to split up our code into fine-grained handlers that only focus and care about one thing, and chain them together to create protocols to handle the rich interactivity and business logic of our apps.

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