Course of Raku / Advanced / Modules / Modules basics

Creating modules

As programs grow, it helps to split them into reusable pieces. A module is a unit of code, kept in its own file, that other programs can load and use.

A module file has the extension .rakumod and begins by naming the module with unit module. Subroutines you write inside are private by default; to make one available to code that uses the module, mark it with the is export trait.

Here is a module stored in a file called Greeting.rakumod:

unit module Greeting;

sub hello($name) is export {
    return "Hello, $name!";
}

The hello subroutine carries is export, so it will be visible to any program that uses the module. A subroutine without is export would stay private to the module.

A module can also share data through our variables, which become reachable through the module’s name. Adding a version number to Greeting is as simple as one more line in the file:

our $version = '1.0';

With that line in Greeting.rakumod, the value is available as $Greeting::version wherever the module is loaded.

The next topics show how a program loads such a module and what exactly it gets from it.

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