asdf:defsystem

(asdf:defsystem name &rest options)

Defines a system — a named collection of source files with load-order constraints — for a later asdf:load-system, and returns the system name as a symbol. This is a limited, API-compatible subset of ASDF's defsystem: the options are plain data and are never evaluated. name is a literal designator (a string "my-lib", a keyword :my-lib, or a symbol). Supported options:

Metadata — :description, :long-description, :version, :author, :maintainer, :license (also :licence), :homepage, :bug-tracker, :source-control, :mailto — accepted for .asd compatibility and ignored.
:depends-on (system...) — systems loaded before this one, located through the same search path as load-system.
:serial t — each component implicitly depends on the previous one.
:components (component...) — the source files: (:file "name" [:depends-on ("other"...)]) names name.lisp; (:module "dir" [:serial t] [:depends-on (...)] :components (...)) prefixes its children with dir/; (:static-file "name") is accepted and contributes no source. Components are loaded in a stable topological order of their :depends-on constraints.

Any other option (:in-order-to, :perform, :defsystem-depends-on, :if-feature, a computed :version, ...) or component type is an error naming the unsupported clause. Normally the form lives in a NAME.asd file next to the sources; a .asd file is parsed as data, so it may contain only defsystem forms (bare or asdf:-qualified) and in-package forms (skipped). An inline top-level (asdf:defsystem ...) in a program also registers the system. Component paths resolve against the directory of the .asd file (or of the defining source).

;; my-lib.asd
(defsystem :my-lib
  :description "A small example system"
  :version "0.1.0"
  :serial t
  :components ((:file "package")
               (:file "main")))

The system loads package.lisp then main.lisp (:serial t), both from the directory of my-lib.asd. See the Systems guide for a complete project walkthrough.