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<ol class="chapter"><li class="chapter-item expanded affix "><a href="title-page.html">The Concur UI Framework</a></li><li class="chapter-item expanded affix "><a href="ch00-00-introduction.html">Introduction</a></li><li class="chapter-item expanded "><a href="ch01-00-getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch01-01-installation.html"><strong aria-hidden="true">1.1.</strong> Installation</a></li><li class="chapter-item expanded "><a href="ch01-02-first-concur-program.html"><strong aria-hidden="true">1.2.</strong> Your first Concur program!</a></li></ol></li><li class="chapter-item expanded "><a href="ch02-00-quick-tour.html"><strong aria-hidden="true">2.</strong> A Quick Tour of Concur</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch02-01-anatomy-of-a-widget.html"><strong aria-hidden="true">2.1.</strong> Anatomy of a Widget</a></li><li class="chapter-item expanded "><a href="ch02-02-widget-return-types.html"><strong aria-hidden="true">2.2.</strong> Widget Return Types</a></li><li class="chapter-item expanded "><a href="ch02-03-composing-widgets.html"><strong aria-hidden="true">2.3.</strong> Composing Widgets</a></li><li class="chapter-item expanded "><a href="ch02-04-event-handling.html"><strong aria-hidden="true">2.4.</strong> Event Handling</a></li><li class="chapter-item expanded "><a href="ch02-05-modifying-dom-on-events.html"><strong aria-hidden="true">2.5.</strong> Modifying DOM on Events</a></li><li class="chapter-item expanded "><a href="ch02-06-handling-multiple-events.html"><strong aria-hidden="true">2.6.</strong> Handling Multiple Events</a></li><li class="chapter-item expanded "><a href="ch02-07-composing-widgets-with-events.html"><strong aria-hidden="true">2.7.</strong> Composing Widgets with Events</a></li><li class="chapter-item expanded "><a href="ch02-08-input-output.html"><strong aria-hidden="true">2.8.</strong> Input Output</a></li></ol></li><li class="chapter-item expanded "><a href="ch03-00-architectural-notes.html"><strong aria-hidden="true">3.</strong> Architectural Notes</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch03-01-replicating-elm-architecture.html"><strong aria-hidden="true">3.1.</strong> Replicating Elm Architecture</a></li><li class="chapter-item expanded "><a href="ch03-02-plan-for-composability-by-breaking-down-components.html"><strong aria-hidden="true">3.2.</strong> Plan for Composability by Breaking Down Components</a></li><li class="chapter-item expanded "><a href="ch03-03-composing-never-ending-widgets.html"><strong aria-hidden="true">3.3.</strong> Composing Never Ending Widgets</a></li></ol></li><li class="chapter-item expanded "><a href="ch04-00-signals.html"><strong aria-hidden="true">4.</strong> Signals</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch04-01-introduction-to-signals.html"><strong aria-hidden="true">4.1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="ch04-02-your-first-signal.html"><strong aria-hidden="true">4.2.</strong> Your First Signal</a></li><li class="chapter-item expanded "><a href="ch04-03-introduction-to-signals.html"><strong aria-hidden="true">4.3.</strong> Converting Display Widgets</a></li><li class="chapter-item expanded "><a href="ch04-04-signal-composition.html"><strong aria-hidden="true">4.4.</strong> Signal Composition</a></li><li class="chapter-item expanded "><a href="ch04-05-signal-example.html"><strong aria-hidden="true">4.5.</strong> Signal Example</a></li><li class="chapter-item expanded "><a href="ch04-06-some-notes-on-signal-usage.html"><strong aria-hidden="true">4.6.</strong> Some Notes on Signal Usage</a></li></ol></li><li class="chapter-item expanded "><a href="ch05-00-faqs.html"><strong aria-hidden="true">5.</strong> FAQs</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch05-01-why-concur.html" class="active"><strong aria-hidden="true">5.1.</strong> Why the Concur Model</a></li><li class="chapter-item expanded "><a href="ch05-02-jumping-into-the-middle-of-widgets.html"><strong aria-hidden="true">5.2.</strong> Jumping Into the Middle of Widgets</a></li></ol></li></ol>
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<h1 class="menu-title">The Concur UI Framework</h1>
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<h1><a class="header" href="#why-the-concur-model" id="why-the-concur-model">Why the Concur Model</a></h1>
<p>Taken from my answer to <a href="https://github.com/jviide/flowponent/issues/2">this question</a></p>
<h2><a class="header" href="#qs-why-the-concur-model" id="qs-why-the-concur-model">Qs. Why the Concur model?</a></h2>
<p>Not a negative sentiment, but legitimately curious.</p>
<p>I checked out the Concur repos and docs + samples to try to get a better understanding of this, but at first-glance it seems like additional complexity that could be handled with plain logical statements in the render method?</p>
<p>If it is not too much trouble, could you explain a bit why using this type of flow is different or better than having a view that gets injected with stateful data and re-renders normally?</p>
<h2><a class="header" href="#ans" id="ans">Ans.</a></h2>
<p>The answer I usually give for Concur is that this flow based paradigm is simpler <em>and</em> scales better to larger programs. This is usually because our mental model fits synchronous control flow, and free composition of widgets better.</p>
<h3><a class="header" href="#its-really-simple-for-simple-real-world-code" id="its-really-simple-for-simple-real-world-code">It's really simple for simple real world code</a></h3>
<p>Think of when a person first learns to program, and writes something beyond plain hello world, which was output only, to something that is interactive.</p>
<p>Say, accept a user's name and then say hello to them. They probably would intuitively write something like this, assuming appropriate <code>getInput</code> and <code>log</code> functions -</p>
<pre><code class="language-purescript">name <- getInput "What is your name"
log "Hello "+name
</code></pre>
<p>This is simple, and works. Hey programming is easy!</p>
<p>But as soon as they start thinking of even slightly larger programs, they have to change their mental model completely. They have to deal with asynchronous behaviour (event handlers), and different input/output modes (interacting with the DOM instead of alert/prompt), and code architecture issues (how do you build a larger program from a smaller one without rewriting completely).</p>
<p>Imagine if writing a simple hello world involved something like this from the get go (In javascript now) -</p>
<pre><code class="language-javascript">setInitialState({name: null})
onRender() {
let {name} = getState()
if(name == null) {
prompt("What is your name",
userInput => setState({name: userInput})
)
} else {
alert("Hello "+name)
}
}
</code></pre>
<p>It's pretty crummy and hard to understand for new programmers, and hides the actual logic behind a lot of cruft.</p>
<p>Concur/Flowponent lets you have the original easy model or programming, without losing anything.</p>
<pre><code class="language-purescript">name <- textInputEnter "What is your name?" true []
D.text $ "Hello " + name
</code></pre>
<p>This code is asynchronous with event handlers, and can output to the dom (<code>textInputEnter</code> and <code>D.div</code> are a part of Purescript-Concur-React).</p>
<p>Also the logic doesn't rely on a magic <code>render</code> method which is called automatically just when you need it to be called (i.e. state changes). Instead, the rendering is explicitly controlled by the program (even if behind the scenes it uses the original render method). I feel it greatly improves comprehension.</p>
<p><strong>AND it scales linearly with program complexity.</strong></p>
<p>Take a very simple extension to the previous program. Think about how the code could be modified to handle a list of users. All of them need to be asked their names and greeted. A new programmer would probably think that it would look something like this (In Javascript) -</p>
<pre><code class="language-javascript">for(user of users) {
let name = prompt("What is your name")
alert("Hello "+name)
}
</code></pre>
<p>It's simple, it's clear, and if it worked it would have had no bugs.</p>
<p>But no. We can't actually write it like that. It takes a great mental leap to get to the state based async model for this functionality.</p>
<p>And because there is so much cruft, there are lots of ways to write this cruft. There isn't one good canonical way. Eventually you have to write something like this. It may have bugs since I just wrote it inline just now (Again in Javascript) -</p>
<pre><code class="language-javascript">// Don't modify the original users array. Assumes a clone method.
setInitialState({usersLeft: users.clone(), name:null})
onRender() {
let {usersLeft, name} = getState()
if(name != null) {
alert("Hello "+name)
}
// No else
let user = usersLeft.pop()
if(user != undefined) {
prompt("What is your name",
// Don't forget to set the modified users array
userInput => setState({usersLeft: usersLeft, name: userInput})
)
}
}
</code></pre>
<p>Whereas, Concur lets you keep the simple model with no drawbacks. -</p>
<p>In Purescript this is simply -</p>
<pre><code class="language-purescript">sequence $ repeat 10 $ do
name <- textInputEnter "What is your name?" true []
D.text $ "Hello " + name
</code></pre>
<p>And even in Javscript it's easy (Using a strange list syntax here because I didn't want to use DOM elements, but hopefully the concept is clear) -</p>
<pre><code class="language-javascript">name = null
for(user of users) {
name = yield step =>
[ if(name != null) alert("Hello "+name)
, prompt("What is your name", step)
]
}
</code></pre>
<p>Looks like programming IS really easy!</p>
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