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10 Miscellaneous additional functionality

FIXME: Add discussion of run-shell-command? Others?

ASDF includes several additional features that are generally useful for system definition and development. These include:

Function: system-relative-pathname system name &key type

It’s often handy to locate a file relative to some system. The system-relative-pathname function meets this need. It takes two arguments: the name of a system and a relative pathname. It returns a pathname built from the location of the system’s source file and the relative pathname. For example

> (asdf:system-relative-pathname 'cl-ppcre #p"regex.data")
#P"/repository/other/cl-ppcre/regex.data"

Instead of a pathname, you can provide a symbol or a string, and optionally a keyword argument type. The arguments will then be interpreted in the same way as pathname specifiers for components. See Pathname specifiers.

Function: system-source-directory system-designator

ASDF does not provide a turnkey solution for locating data (or other miscellaneous) files that are distributed together with the source code of a system. Programmers can use system-source-directory to find such files. Returns a pathname object. The system-designator may be a string, symbol, or ASDF system object.

Function: clear-system system-designator

It is sometimes useful to force recompilation of a previously loaded system. In these cases, it may be useful to (asdf:clear-system :foo) to remove the system from the table of currently loaded systems; the next time the system foo or one that depends on it is re-loaded, foo will then be loaded again. Alternatively, you could touch foo.asd or remove the corresponding fasls from the output file cache. (It was once conceived that one should provide a list of systems the recompilation of which to force as the :force keyword argument to load-system; but this has never worked, and though the feature was fixed in ASDF 2.000, it remains cerror’ed out as nobody ever used it.)

Note that this does not and cannot by itself undo the previous loading of the system. Common Lisp has no provision for such an operation, and its reliance on irreversible side-effects to global datastructures makes such a thing impossible in the general case. If the software being re-loaded is not conceived with hot upgrade in mind, this re-loading may cause many errors, warnings or subtle silent problems, as packages, generic function signatures, structures, types, macros, constants, etc. are being redefined incompatibly. It is up to the user to make sure that reloading is possible and has the desired effect. In some cases, extreme measures such as recursively deleting packages, unregistering symbols, defining methods on update-instance-for-redefined-class and much more are necessary for reloading to happen smoothly. ASDF itself goes through notable pains to make such a hot upgrade possible with respect to its own code, and what it does is ridiculously complex; look at the beginning of asdf.lisp to see what it does.


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