Hello, Elm!


Default Module Declaration

If you forget to add a module declaration at the top of an Elm file, Elm will put everything in a Main module like so:

module Main exposing (..)

Installing Project Dependencies

In an empty project directory, running elm package install generates a new elm-package.json file and adds dependencies for the elm-lang/core, elm-lang/html, and elm-lang/virtual-dom packages.

However, if an elm-package.json file already exists in a project directory, then running elm package install will install all the package dependencies listed in that elm-package.json file. That means you can download an Elm project and run elm package install to install all the dependencies of that project in one fell swoop!

To install a specific package, specify the package name like so:

elm-package install elm-lang/html

That downloads the latest version of the elm-lang package that's compatible with the installed version of Elm. And the elm-package.json file is automatically updated to include the new package dependency.

To install a specific version of a package, include the version number like so:

elm-package install elm-lang/html 3.0.0

Reactor Options

By default, the Elm reactor fires up on localhost port 8000. You can change the address and/or port by specifying --address and --port options. For example, here's how to run on the address using port 9000:

elm reactor --address= --port=9000

Code So Far

The code for this video is in the hello-elm directory found within the video-code directory of the code bundle.