6.1 The defsystem form

This section begins with an example of a system definition, then gives the full grammar of defsystem.

Let’s look at a simple system. This is a complete file that should be saved as hello-lisp.asd (in order that ASDF can find it when ordered to operate on the system named "hello-lisp").

;; Usual Lisp comments are allowed here

(defsystem "hello-lisp"
  :description "hello-lisp: a sample Lisp system."
  :version "0.0.1"
  :author "Joe User <joe@example.com>"
  :licence "Public Domain"
  :depends-on ("optima.ppcre" "command-line-arguments")
  :components ((:file "packages")
               (:file "macros" :depends-on ("packages"))
               (:file "hello" :depends-on ("macros"))))

Some notes about this example:

• The defsystem form defines a system named hello-lisp that contains three source files: packages.lisp, macros.lisp and hello.lisp.
• The .lisp suffix is implicit for Lisp source files. The source files are located in the same directory as the .asd file with the system definition.
• The file macros depends on packages (presumably because the package it’s in is defined in packages), and the file hello depends on macros (and hence, transitively on packages). This means that ASDF will compile and load packages then macros before starting the compilation of file hello.
• This example system has external dependencies on two other systems, optima.ppcre (that provides a friendly interface to matching regular expressions), and command-line-arguments (that provides a way to parse arguments passed from the shell command line). To use this system, ASDF must be configured to find installed copies of these systems; it will load them before it tries to compile and load hello-lisp.
• This system also defines a bunch of metadata. While it is optional to define these fields (and other fields like :bug-tracker, :mailto, :long-name, :long-description, :source-control), it is strongly recommended to define the fields :description, :version, :author, and :licence, especially if you intend your software to be eventually included in Quicklisp.
• Make sure you know how the :version numbers will be parsed! Only period-separated non-negative integers are accepted at present. See Version specifiers.
• This file contains a single form, the defsystem declaration. No in-package form, no asdf: package prefix, no nothing. Just the one naked defsystem form. This is what we recommend. More complex system definition files are possible with arbitrary Lisp code, but we recommend that you keep it simple if you can. This will make your system definitions more robust and more future-proof.

This is all you need to know to define simple systems. The next example is much more involved, to give you a glimpse of how you can do more complex things. However, since it’s ultimately arbitrary Lisp code, there is no bottom to the rabbit hole.