Your First Program

A guided tour of a complete mType program. We'll write a tiny todo-list app that exercises classes, generics, lambdas, the standard library, and string interpolation.

The Program

Save as todo.mt:

import * from "lib/collections/ArrayList.mt";

class Todo {
    private string title;
    private bool done;

    public constructor(string title) {
        this.title = title;
        this.done = false;
    }

    public function complete(): void {
        this.done = true;
    }

    public function toString(): string {
        string mark = this.done ? "[x]" : "[ ]";
        return $"{mark} {this.title}";
    }
}

function main(): void {
    ArrayList<Todo> todos = new ArrayList<Todo>();
    todos.add(new Todo("Read the docs"));
    todos.add(new Todo("Write a program"));
    todos.add(new Todo("Ship it"));

    todos.get(0).complete();

    for (Todo t : todos) {
        print(t.toString());
    }
}

main();

Run it:

mType todo.mt

Output:

[x] Read the docs
[ ] Write a program
[ ] Ship it

What This Demonstrates

Feature	Where
Imports	import * from "lib/collections/ArrayList.mt"; — pulls a generic ArrayList<T> from the standard library.
Class declaration	class Todo { ... } — fields, constructor, methods.
Access modifiers	private string title; and public constructor(...).
Generic instantiation	new ArrayList<Todo>() — explicit type argument.
String interpolation	$"{mark} {this.title}" — $"..." strings inline expressions.
Enhanced for	for (Todo t : todos) { ... } — iterate any Iterable<T>.
Standard library	ArrayList<T> from lib/collections/.

Next Steps

• Read the Language Reference for the full syntax.
• Browse the Standard Library for what's available out of the box.
• Try the Async/Await page for a concurrency example.