Elm

If you are new to Elm, learn more about the language here and try it out in the online interactive editor.

This is the Elm compiler and server, allowing you to natively develop Elm applications that run in any modern browser. The compiler generates HTML and JS files, and the server just serves .elm files directly.

If you intend to serve Elm code with a custom Haskell backend, be sure to read all the way to the "Installation for Haskell-Users" section.

Installation for General Use

Download the Haskell Platform 2012.2.0.0. This will give you access to the Haskell compiler (needed to build Elm) and Haskell's package distribution system (to make installation of Elm easier). Elm definitely works with version 7.4 of the Haskell compiler (i.e. GHC 7.4) which is bundled with version 2012.2.0.0 of the Haskell Platform.

If you are a Linux user and already have a copy of GHC installed and have downloaded a bunch of packages, it may be worthwhile to create new user account and just install Elm separately as described here. Dependency issues have been rampant lately with packages changing to support GHC 7.6.

If you run into issues, check the mailing list for advice or go to the #Elm IRC channel.

Installing the compiler and server

Once the Haskell Platform is installed (even if it already was), you must update your listing of packages with:

cabal update

This will ensure that the elm package is available. Then install Elm with:

cabal install elm

Assuming everything goes correctly (potential problems are discussed later), this will install the elm compiler on your machine. elm is a standard compiler that takes .elm files and produces .html and/or .js files. You can then use these files with your favorite web-framework. Use elm --help for more directions on how to use it.

If you have this installed you can write and compile Elm locally, so if the next step fails for you, it is safe to proceed without it.

You can also install elm-server which is both a compiler and server, allowing you to develop without designing and setting up a server yourself. Running elm-server starts a server in the current directory. It will compile and serve any .elm files in the current directory and its sub-directories. This is how I prefer to develop Elm programs. Install with:

cabal install elm-server

Dependency issues have been cropping up with this step, so if you run into issues, please report them so they can be fixed! Once installed, use the command elm-server --help to see some extra information.

Using the Elm compiler and server

To use these executables you need to add a new directory to your PATH. For me, the executables were placed in /home/evan/.cabal/bin which I appended to the end of my PATH variable in my .bashrc file. Cabal should tell you where your executables are located upon successful installation, so you can make a similar addition (see this tutorial if you are new to changing your PATH in Unix/Linux).

You can use the commands elm --help and elm-server --help to get more information about using these tools.

That is almost everything. Now, we will create a simple Elm project. The following commands will set-up a very basic project and start the Elm server.

mkdir helloElm
cd helloElm
echo main = lift asText Mouse.position > main.elm
elm-server

The first two commands create a new directory and navigate into it. The echo command places a simple program into main.elm (do this manually if you do not have echo). The final command starts the Elm server at localhost, allowing you to navigate to main.elm and see your first program in action.

Installation for Haskell-users

The elm package provides support for compilation of Elm code directly in Haskell and QuasiQuoting. See the Examples/ directory for information and examples on how to get started with Elm+Haskell.

Yesod users should also install the elm-yesod package which provides functions for idiomatically embedding Elm in Yesod:

cabal install elm-yesod

Some extra tips on Elm+Yesod can be found here.

An important note: When you install the elm compiler, it automatically downloads Elm's JavaScript runtime system to ~/.cabal/share/Elm-x.y.z/. The runtime system will follow the name scheme elm-runtime-x.y.z.js where x.y.z matches the version number of the compiler. If you want to serve this file from a different location, copy it from its home and always be sure that code compiled with version x.y.z of the compiler is served with version x.y.z of the runtime system.

Potential problems and their solutions

• Try cabal install elm. This will give you access to the elm executable (but not elm-server).

These problems all appeared before Elm version 0.1.1.4:

• Install errors having to do with happstack-server-7.0.2. This version of happstack-server has stricter dependency restrictions that conflict with other libraries required by Elm. Try installing with an earlier version of happstack-server with the following command: cabal install elm --constrain="happstack-server<7.0.2"
• When installing on Debian, blaze-html-0.4.3.2 fails to compile. You must install blaze-html-0.4.3.1 instead.
• Elm does not appear to work with the latest versions of containers (i.e. 0.4.2.*). I know it works with earlier versions of containers, so to avoid this problem, you can try: cabal install elm --constrain="containers==0.4.1.0" --force-reinstall
• On Windows, HAppStack has trouble installing because of issues with the "network" package. I struggled with this problem on Windows 7 until I found the suggestion at the bottom of this page.

If you are still stuck, email the list or ask a question in the #Elm IRC channel.