Course of Raku / Advanced / Modules

Module introspection

A module’s name introduces a package — a namespace that holds the names defined in it. Earlier, in the section about containers, you met WHO, which returns the Stash (the symbol table) of a package. Module introspection puts that to use.

The examples below use the Greeting module built up in the earlier topics — an exported subroutine and a shared our variable:

unit module Greeting;

our $version = '1.0';

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

The package of a module is written with a trailing ::. Adding .keys lists the names it contains:

use Greeting;

say Greeting::.keys.sort; # ($version EXPORT)

The Greeting module from the earlier topics defines an our variable, $version, so its package contains that name — with the sigil included. Next to it sits EXPORT, which may look surprising. It is a package Raku creates automatically to hold everything a module marks is export, such as the hello subroutine. An exported name therefore does not appear directly in the package; it lives inside that EXPORT sub-package. (The keys come back in no fixed order, so the example sorts them for a stable result.)

You can also look a name up in the package by using it as a key. This reaches the same value as the qualified $Greeting::version:

use Greeting;

say Greeting::{'$version'}; # 1.0

Listing what a module exports

The EXPORT package seen above is where the exported names actually live, so you can list them by looking one level deeper. Exports without a tag go into the DEFAULT group (see Export tags), and its .keys are the exported routines:

use Greeting;

say Greeting::EXPORT::DEFAULT::.keys.sort; # (&hello)

Each key is an exported name with its sigil — here the single subroutine &hello, shown with the & that marks a routine. This is how you discover what a module makes available to its users without reading its source: ask its EXPORT::DEFAULT package what it holds.

Introspecting a package this way is handy when you want to discover what a module provides, or to reach its names dynamically rather than writing each one out in the source code.

Course navigation

← Solution: Load at run time   |   List the symbols →