— Function: find-system system-designator &optional (error-p t)

Given a system designator, find-system finds and returns a system. If no system is found, an error of type missing-component is thrown, or nil is returned if error-p is false.

To find and update systems, find-system funcalls each element in the *system-definition-search-functions* list, expecting a pathname to be returned. The resulting pathname is loaded if either of the following conditions is true:

• there is no system of that name in memory
• the file's last-modified time exceeds the last-modified time of the system in memory

When system definitions are loaded from .asd files, a new scratch package is created for them to load into, so that different systems do not overwrite each others operations. The user may also wish to (and is recommended to) include defpackage and in-package forms in his system definition files, however, so that they can be loaded manually if need be.

The default value of *system-definition-search-functions* is a function that looks in each of the directories given by evaluating members of *central-registry* for a file whose name is the name of the system and whose type is asd. The first such file is returned, whether or not it turns out to actually define the appropriate system. Hence, it is strongly advised to define a system foo in the corresponding file foo.asd.