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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" class="active"><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"><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><a class="header" href="#input-output" id="input-output">Input Output</a></h1>
<p>Concur provides seamless IO at widget boundaries. This is another area where other frameworks falter. Since concurrency is baked into and integral to Concur, IO becomes predictable and powerful. Concur provides lifting functions to lift IO into widgets, and those lifted io widgets can be easily composed just like any other normal widget.</p>
<p>Continuing our previous example, if we want to print the greeting selected by the user to the console.</p>
<pre><code class="language-purescript">helloWidget :: forall a. Widget HTML a
helloWidget = do
greeting <- div'
[ "Hello" <$ button [onClick] [text "Say Hello"]
, "Namaste" <$ button [onClick] [text "Say Namaste"]
]
liftEffect (log ("You chose to say " <> greeting))
text (greeting <> " Sailor!")
</code></pre>
<p>Here we use <code>liftEffect</code> to convert an effect into a widget. In Haskell, we can use <code>liftIO</code>.</p>
<p>Lifting IO to Widgets means we can compose IO in parallel with other Widgets. This can lead to some nice patterns. Two examples -</p>
<ol>
<li>Allow cancelling long running IO actions in response to GUI events, without any boilerplate. Let's say we want to create a timer which can be cancelled. The following widget will return when the timer completes after a specified duration, or when the button is pressed, whichever is first. Whenver the button is pressed, the timer thread is automatically cancelled so you don't have to do that manually.</li>
</ol>
<pre><code class="language-purescript">timerWidget ms = liftAff (delay (Milliseconds ms)) <|> button [unit <$ onClick] [text "Cancel"]
</code></pre>
<ol start="2">
<li>Show a "Loading" screen while performing IO, let's say while making an ajax call.</li>
</ol>
<pre><code class="language-purescript">resp <- liftAff (AX.get ResponseFormat.json url) <|> text "Fetching posts from subreddit..."
</code></pre>
<p>Also note that the ability to perform IO actions from Widgets is very handy when creating bindings to existing native/JS libraries.</p>
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