Using a library

This page describes how to use a library in Pen. It consists of the following steps:

  1. Add a library package as a dependency in another package.
  2. Import functions and types from the library package.

Modifying package configuration

To use a library package, you need to add the package as a dependency in another package. To add the dependency, you modify a pen.json configuration file in the package adding the library package's name (e.g. Foo) and URL (e.g. git:// in a dependencies field like the following example. Note that you need to specify a git protocol scheme for library packages published as Git repositories. For other kinds of library packages, see Package configuration.

  "type": "application", // This can be any type.
  "dependencies": {
    "Foo": "git://"

Importing functions and types from a library package

To import functions and types from the library package, you use import statements in a source file of your module with a name of the library package (e.g. Foo) and a module name (e.g. Math) where functions or types you want to use are defined.

import Foo'Math

Then, you are ready to use those functions and types with a prefix of the module name! For example, to call a function named Add in the Math module, you can write Math'Add(x, y).

type MyType = Math'Order

MyFunction = \(x number, y number) number {
  Math'Add(x, y)

Next steps