A component represents a source file or
(recursively) a collection of components.
A system is (roughly speaking) a top-level component
that can be found via
A system designator is a string or symbol and behaves just like any other component name (including with regard to the case conversion rules for component names).
Given a system designator,
find-systemfinds and returns a system. If no system is found, an error of type
missing-componentis thrown, or
nilis returned if
To find and update systems,
find-systemfuncalls each element in the
*system-definition-search-functions*list, expecting a pathname to be returned, or a system object, from which a pathname may be extracted, and that will be registered. The resulting pathname (if any) is loaded if one of the following conditions is true:
- there is no system of that name in memory
- the pathname is different from that which was previously loaded
- the file's
last-modifiedtime exceeds the
last-modifiedtime 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
in-packageforms 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 list of two functions. The first function 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. The second function does something similar, for the directories specified in the
source-registry. Hence, it is strongly advised to define a system foo in the corresponding file foo.asd.