modularize is an attempt at providing a common interface to segregate major application components. This is achieved by adding special treatment to packages. Each module is a package that is specially registered, which allows it to interact and co-exist with other modules in better ways. For instance, by adding module definition options you can introduce mechanisms to tie modules together in functionality, hook into each other, and so on.
Each module should consist of a define-module form and an ASDF system with the superclass modularize:module. define-module acts as a wrapper around defpackage, so it will replace your usual defpackage form. Any option you would use in defpackage is also usable in define-module, but the latter also allows for custom-defined options that perform specific actions upon module creation.
(modularize:define-module test-module
(:use #:cl #:modularize)
(:export #:greet))
If for some reason you absolutely do not want to use define-module, you may define your package manually and call modularize on it afterwards. Note though that you also need to manually perform all changes that additional module options may otherwise perform for you. If your module-name somehow differs from the ASDF system, you will need to specify this in your ASDF system definition:
(asdf:defsystem some-test-module
:class "modularize:virtual-module"
:defsystem-depends-on (:modularize)
:module-name "test-module"
...)
The main difference from packages is that each module has a central storage table, which you can access with module-storage. This allows you to save metadata on modules to keep track of the different parts each module might play in your application.
Another function that might prove useful is delete-module, which attempts to offer a mechanism to completely remove a module so as to revert its changes. Without any further additions, this will simply result in all symbols in the module package being makunbound and fmakunbound and the package getting deleted. Since a module might also cause changes outside of its own package, it is therefore advised to add deletion hooks through define-delete-hook, so as to make sure other kinds of changes can be cleaned up as well.
Similarly, if you want to tack on functionality to initialize a module once it is defined, you can hook into that with define-modularize-hook and define-option-expander. The former works like define-delete-hook, and is called once modularize is called on a package after the package's storage has been set up. The latter allows you to declare custom forms that a define-module call should expand to. Note that module options are only expanded after modularize is called, so you may use the storage in your expansions.
If a component should extend the functionality of another, this can be more intuitively done through define-module-extension. In looks and form it is the same as define-module, with the difference that it won't create a new package, but use the one it is extending. Through this you can export new functions and other additions without running into a multiple-package mess.
If you would like to group multiple packages under a single module (probably the case if you use one package per file), then you must register the packages with the module. You can do this in your module definition with the :packages option, or by module-packages calls.
For a super small sample use of a module, have a look at modularize-test-module.asd and modularize-test-module.lisp. For extensions to the module system, have a gander at modularize-interfaces and modularize-hooks.
