How to use the command `elm` (with examples)

Elm is a functional programming language that compiles to JavaScript and is used for web development. The elm command provides various functionalities to work with Elm projects, such as initializing a project, running an interactive shell, compiling Elm files, starting a local web server, and installing Elm packages.

Use case 1: Initialize an Elm project (elm init)

Code:

elm init

Motivation: Initializing an Elm project is the first step to start working with Elm. It creates an elm.json file, which is used for managing the project’s dependencies and configuration.

Explanation: The elm init command initializes an Elm project by creating an elm.json file in the current directory. This file contains the project’s metadata, such as name, version, and dependencies.

Example output:

Success! Created elm.json and elm-stuff directory.

Use case 2: Start interactive Elm shell (elm repl)

Code:

elm repl

Motivation: The Elm REPL (Read-Eval-Print Loop) allows developers to experiment with Elm code interactively. It provides a convenient way to test small code snippets or explore the functionality of the Elm language.

Explanation: The elm repl command starts an interactive Elm shell, where you can enter Elm expressions and see their results immediately. It provides a convenient way to test code, debug, and explore the Elm language.

Example output:

Elm REPL 0.19.1 - Press Ctrl+C to exit.
> "Hello, World!"
"Hello, World!"
>

Use case 3: Compile Elm file to HTML (elm make)

Code:

elm make source

Motivation: Compiling Elm files to HTML allows developers to create Elm applications that can be embedded in web pages.

Explanation: The elm make command compiles an Elm file to JavaScript and generates an index.html file with the necessary scripts and markup to run the Elm application in a web browser. The source argument specifies the name of the Elm file.

Example output:

Success!

    Main ───> index.html

Use case 4: Compile Elm file to JavaScript (elm make with –output)

Code:

elm make source --output=destination.js

Motivation: Compiling Elm files to JavaScript provides developers with the flexibility to integrate Elm code into existing JavaScript projects.

Explanation: The elm make command can output the compiled Elm code as JavaScript instead of generating an index.html file. The --output flag specifies the destination file for the compiled JavaScript. The source argument specifies the name of the Elm file.

Example output:

Success! Compiled 1 module.
Succesfully generated JavaScript code in destination.js

Use case 5: Start local web server (elm reactor)

Code:

elm reactor

Motivation: The Elm reactor provides a convenient way to develop Elm applications by automatically compiling Elm files and serving them on a local web server.

Explanation: The elm reactor command starts a local web server that watches for changes in Elm files. It automatically recompiles the Elm files and serves them, allowing you to see the changes in real-time without manually triggering the compilation.

Example output:

Go to <http://localhost:8000> to see your project dashboard.

Use case 6: Install Elm package (elm install)

Code:

elm install author/package

Motivation: Elm packages provide pre-built functionality and libraries that developers can use to enhance their Elm projects. Installing a package allows developers to leverage the existing Elm ecosystem.

Explanation: The elm install command installs Elm packages from the official Elm package repository https://package.elm-lang.org . The author/package argument specifies the package to be installed, where author is the package author’s username and package is the package name.

Example output:

Successfully installed author/package 1.0.0

Conclusion:

The elm command provides various functionalities for working with Elm projects. From initializing a project to compiling Elm files, starting a web server, and installing packages, it covers essential aspects of Elm development. These examples demonstrate the versatility and power of the Elm command-line interface in supporting and enhancing the development workflow for Elm applications.