$ echo kbmackenzie

Language Extensions

To extend one of the project templates that come with Mewlix, all you need to do is override the template's index.js file.

It can be done in 3 simple steps:

1. Create an index.js file in your project's root.
2. Add some basic boilerplate:
   • Import the initializer function from the ./init.js script.
   • Define your extension as a callback to the initializer function.
   • Export everything as a void function. This should be your script's default export.
3. List your index.js file as an asset in your project file's assets field.

A simple example of a language extension can be found below.

/* A small language extension that makes the 'meow' expression use window.alert().
 * It will only work in web project modes (console, graphic and blank). */
import init from './init.js';
export default () => init(mewlix => {
  mewlix.setMeow(x => window.alert(x));
});

As you can see, the initializer function accepts the Mewlix object as argument.

The Mewlix object also exposes a few useful API functions under Mewlix.api, such as:

• Mewlix.api.box(object): Create a new box from a regular JavaScript object.
• Mewlix.api.shelf(...items): A variadic function that creates a shelf from its arguments.
• Mewlix.api.inject(key, object): An API function for creating yarn balls. The object passed as a second argument should contain all fields you want your yarn ball to export.

/* A small language extension that adds a silly example yarn ball.
 * It will only work in web project modes (console, graphic and blank). */
import init from './init.js';
export default () => init(mewlix => {
  mewlix.api.inject('cats', {
    cats: mewlix.api.shelf('jake', 'princess', 'tiger'),
    sayMeow() { window.alert('meow meow'); },
  });
});

Note: The callback function passed to the initializer function is allowed to return a Promise, and that Promise will be awaited.