Using a Mason Package

Once mason has been installed, you are all ready to get started using mason packages! This section outlines a quick hands-on approach to getting started with mason packages as dependencies in your own code.

A Mason Hello World!

So, mason is installed and mason --help is working, showing the available mason subcommands. What now?

First, let’s create a new directory to house our mason project. This will give us everything we need to start installing dependencies from the mason registry while keeping our directory structure nice and clean.

mason new HelloPackage
cd HelloPackage

At this point, mason will start prompting you for some basic information about your package. Since this package is just for getting started, all that you need to worry about for now is the package name.

You can name your package whatever you would like, as long as it is a valid Chapel identifier, but for simplicity, let’s name our package HelloPackage and then go with the default values for all other prompts, leaving them blank.

If everything has gone as planned, you should be met with the prompt: “Initialized new library project: HelloPackage”. Now, let’s get installing our first mason package…

To view all available packages, run the mason search command. This will output a list of all packages registered to the mason registry, which can be viewed at

The package that we are interested in with this tutorial is the HelloWorld package. Let’s signal to mason that we would like to install that package:

mason add HelloWorld@0.1.0

This will add the HelloWorld package to our Mason.toml file as a dependency (you can open the Mason.toml file to see the change).

Now, everything is ready to go with our HelloPackage program… now the fun part: writing (or copying, in this case) some code.

Open up the package source file located at ./src/HelloPackage.chpl. You should see something like this:

/* Documentation for HelloPackage */
module HelloPackage {
  writeln("New library: HelloPackage");

This program will run as-is, but we aren’t using our HelloWorld dependency just yet. In order to use the package, we need to add a use HelloWorld to bring in the dependency. This gives us access to the whole module namespace of the HelloWorld package, and we can call all of the available functions.

Let’s call the helloChapelFriends() function to make sure that it worked. Now, the code should look like this:

/* Documentation for HelloPackage */
module HelloPackage {
  use HelloWorld;

At this point, everything should be good to go! Time to run the program.

After double-checking that you are in the top-level directory of the mason project that you’ve been working in (named HelloWorld/ in this tutorial), now we can install our dependency and build our program with the command:

mason build

After running this command, the HelloWorld package will be installed to MASON_HOME, which defaults to ~/.mason, so, assuming MASON_HOME has not been modified, the source code of all mason dependencies can be found at ~/.mason.

If everything has worked up until now, it’s time to run our program!

mason run

You should see a “Hello Chapel friends from Mason” message printed to the screen. Congratulations! You can now install mason dependencies and use them in your code.

Hello World Tutorial Cheat Sheet

  1. mason init

  2. mason add HelloWorld@1.0.0

  3. add use HelloWorld; and helloChapelFriends(); to Chapel module in ./src/ directory

  4. mason build

  5. mason run