12.2 Defining a system
12.2.5 Examples
Consider an example system,demo, defined as follows:
(defsystem demo (:package "USER")
:members ("parent"
"child1"
"child2")
:rules ((:in-order-to :compile ("child1" "child2")
(:caused-by (:compile "parent"))
(:requires (:load "parent")))))
This system compiles and loads members into theUSER package if the members themselves do not specify packages. The system contains three members --parent,child1, andchild2 -- which may themselves be either files or other systems. There is only one explicit rule in the example. Ifparent needs to be compiled (for instance, if it has been changed), then this causeschild1 andchild2 to be compiled as well, irrespective of whether they have themselves changed. In order for them to be compiled,parent must first be loaded.
Implicitly, it is always the case that if any member changes, it needs to be compiled when you compile the system. The explicit rule above means that if the changed member happens to beparent, then every member gets compiled. If the changed member is notparent, thenparent must at least be loaded before compiling takes place.
The next example shows a system consisting of three files:
(defsystem my-system
(:default-pathname "~/junk/")
:members ("a" "b" "c")
:rules ((:in-order-to :compile ("c")
(:requires (:load "a"))
(:caused-by (:compile "b")))))
What plan is produced when all three files have already been compiled, but the fileb.lisp has since been changed?
First, filea.lisp is considered. This file has already been compiled, so no instructions are added to the plan.
Second, fileb.lisp is considered. Since this file has changed, the instruction compile b is added to the plan.
Finally filec.lisp is considered. Although this has already been compiled, the clause
(:caused-by (:compile "b"))
causes the instruction compile c to be added to the plan. The compilation ofc.lisp also requires thata.lisp is loaded, so the instruction load a is added to the plan first. This gives us the following plan: