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Hello, World!

Let's start with the most basic Inko program: a program that writes "Hello, World" to STDOUT.

Create a file called hello.inko with the following contents:

import std.stdio.STDOUT

class async Main {
  fn async main {'Hello, World!')

Now run it as follows:

inko run hello.inko

If all went well, the output is "Hello, World!".

Breaking it down

Let's break down what the program does. We first encounter the following line:

import std.stdio.STDOUT

This imports the STDOUT type from the std.stdio module, provided by the standard library. Inko doesn't expose a print method of sorts by default, as not every program needs to write to STDOUT or STDERR. As such, we have to explicitly import the necessary type. If we wanted to write to STDERR, we'd instead use the following import:

import std.stdio.STDERR

We can also import both:

import std.stdio.(STDERR, STDOUT)

After the import we encounter the following:

class async Main {
  fn async main {


Inko uses lightweight processes (more on that later), which are defined using the syntax async class NAME { ... }. The main process is always called "Main", and is required to define an "async" instance method called "main".

The final line writes the message to STDOUT:'Hello, World!')

STDOUT is a regular class, and to use it we must first create an instance of it using the new static method. The print method is then used to write the given String to STDOUT.