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Colin Webb

Using Elm in Octopress

Elm is a functional programming language aimed at the browser. It aims to replace all HTML, CSS, and JavaScript code. It borrows a lot from Haskell, and promises that if your Elm code compiles, it will run without exceptions.

*Update = 2017-05-18*

My blog no longer uses Octopress, and it now uses Hakyll instead. The process and results using Hakyll are remarkably similar though.

Animated, or interactive, examples can greatly enhance blog posts. This is ultimately achieved via embedding HTML, CSS, and JavaScript. My blog is powered by Octopress, and instead of writing HTML, CSS, and JavaScript, I was interested in using Elm instead.

Including JavaScript in an Octopress Post

Running arbitary JavaScript in Octopress is easy. The code below will insert an HTML paragraph into a div.

<div id="elm-goes-here"></div>
<script type="text/javascript">
  var element = document.getElementById("elm-goes-here");
  element.innerHTML = "<p>This is set via JavaScript!!</p>";

Instead of inlining the JavaScript, you can include it in the source/javascripts/ directory. After publishing, that directory is made available as /javascripts/

Including Elm in an Octopress Post

As we can use arbitary JavaScript in an Octopress blog post, we can follow a few simple steps, and have the browser running our Elm code instead!

Elm has interop with JavaScript through HTML embedding (and a couple of other ways). In order to embed in a div, we first need to write and then compile our Elm code.

elm-make Stamps.elm –output=app.js

Once compiled, and made available by placing it in the source/javascripts/ directory, we can then include it in the blog post.

<div id="elm-goes-here"></div>
<script type="text/javascript" src="/javascripts/app.js"></script>
  var element = document.getElementById("elm-goes-here")
  Elm.embed(Elm.Stamps, elmDiv);

As a demonstration, have a quick play with the interactive section below. It is an embedded version of Elm's Stamps Example. Elm.embed requires a module to import, so if you'd like to try this yourself, add the following to the top of your Elm code.

module Stamps where

If you don't like pentagons, there are lots of other Elm examples to play around with.