2.2 A more involved example

Let's illustrate some more involved uses of defsystem via a slightly convoluted example:

     (defsystem "foo"
       :version "1.0"
       :components ((:module "foo" :components ((:file "bar") (:file"baz")
                                                (:file "quux"))
     	        :perform (compile-op :after (op c)
     			  (do-something c))
     		:explain (compile-op :after (op c)
     			  (explain-something c)))
                    (:file "blah")))

The method-form tokens need explaining: essentially, this part:

     	        :perform (compile-op :after (op c)
     			  (do-something c))
     		:explain (compile-op :after (op c)
     			  (explain-something c))

has the effect of

     (defmethod perform :after ((op compile-op) (c (eql ...)))
     	   (do-something c))
     (defmethod explain :after ((op compile-op) (c (eql ...)))
     	   (explain-something c))

where ... is the component in question; note that although this also supports :before methods, they may not do what you want them to – a :before method on perform ((op compile-op) (c (eql ...))) will run after all the dependencies and sub-components have been processed, but before the component in question has been compiled.