|Allegro CL version 8.1|
Unrevised from 8.0 to 8.1.
This document contains the following sections:1.0 Packages introduction
Common Lisp allows the use of packages to keep different parts of an application separate, permitting multiple use of symbol names and independent development of different parts of a large program. As delivered, Allegro CL comprises several packages, and users should be aware of which packages are available, which should be used by the user, and which should, in general, be avoided.
Starting in release 6.0, Allegro CL has implemented a hierarchical package naming scheme, allowing the specification of a hierarchy of packages, and the use of relative package specifiers, analogous to relative pathnames. While this facility is an extension to the ANSI spec, programs that do not use hierarchical naming are unaffected (except for the handling of rather unusual, erroneous code). Programs that use it, however, may have to be modified to be portable. See Section 2.0 Hierarchical Packages.
Lisp permits already-defined functions to be redefined dynamically. However, redefining system-defined functions (either from the Common Lisp standard in the common-lisp package or from the Allegro CL implementation, in packages such as excl, system, etc.) is almost always a bad idea. Allegro CL implements a package-locking system which protects symbols in reserved packages from new or changed function definitions. See the discussions under the heading Section 6.0 Package locking and package definition locking below.
The Common Lisp package system, designed and standardized some years ago, is not hierarchical. Since Common Lisp was standardized, other languages, including Java and Perl, have evolved namespaces which are hierarchical. This document describes a hierarchical package naming scheme for Common Lisp. We hope that CL implementations other than just Allegro CL will include this facility. All the source code used in Allegro CL to implement the facility is included below.
The goals of hierarchical packages in Common Lisp are:
In a nutshell, a dot (.) is used to separate levels in package names, and a leading dot signifies a relative package name. Absolute package names require no modifications to the underlying CL implementation. Relative package names require small and simple modifications, for which the source code is given below.
The choice of dot follows Java. Perl, another language with hierarchical packages, uses a colon (:) as a delimiter, but the colon is already reserved in Common Lisp.
Franz intends to extend the hierarchy below to currently existing packages. The Allegro CL test harness (see test-harness.htm) is in the util.test package.
Relative package names are needed for the same reason as relative pathnames, for brevity and to reduce the brittleness of absolute names.
A relative package name is one that begins with one or more dots. A single dot means the current package, two dots mean the parent of the current package, and so on.
Here are some examples, assuming that packages named mypack,
foo.bar, have all been created:
|relative name||current package||absolute name of referenced package|
Note 1: To repeat what we said just before the table, all packages in the hierarchy must exist.
Note 2: WARNING ABOUT NICKNAMES! Unless you
provide nicknames for your hierarchical packages (and we recommend
against doing so because the number gets quite large), you can only
use the names supplied. You cannot mix in nicknames or alternate
nicknames of the
common-lisp-user package. Consider
When the current package (the value of
you might expect
.foo to refer to
cl-user.foo, but it does not. It refers to the
that the purpose of nicknames is to provide shorter names in place of
the longer names designed to be fully descriptive. The hope is that
hierarchical packages makes longer names unnecessary and thus makes
Note 3: multiple dots can only appear at the
foo.bar..baz does not mean
foo.baz -- it is invalid. (Of course, it is
perfectly legal to name a package
find-package will not
process such a name to find
foo.baz in the package
The implementation of hierarchical packages modifies find-package and provides certain auxiliary functions, package-parent, package-children, and relative-package-name-to-package, as described in this section. (defpackage itself requires no modification.)
While the changes to find-package are small and described below, it is an important consideration for authors who would like their programs to run on a variety of implementations that using hierarchical packages will work in an implementation without the modifications discussed in this document. We show why not after describing the changes to find-package.
Absolute hierarchical package names require no changes in the underlying CL implementation.
Using relative hierarchical package names requires a simple modification of find-package.
In ANSI CL, find-package,
if passed a package object, returns it; if passed a string, find-package looks for a package with
that string as its name or nickname, and returns the package if it
finds one and returns
nil if it does not; if passed
a symbol, the symbol name (a string) is extracted and find-package proceeds as it does
with a string.
For implementing hierarchical packages, the behavior when the
argument is a package object (return it) does not change. But when the
argument is a string starting with one or more dots not directly
naming a package, find-package
will, instead of returning
nil, check whether the
string can be resolved as naming a relative package, and if so, return
the associated absolute package object. (If the argument is a symbol,
the symbol name is extracted and find-package proceeds as it does with a
In Allegro CL, find-package
passes a string to the function
excl::package-name-to-package, which returns a
package object or
nil. Without hierarchical
packages, find-package returns
nil. With hierarchical packages, if
nil, find-package calls
excl::relative-package-name-to-package, which again returns
a package object or
is returned at this point, cl:find-package returns
The complete source code for the modifications made to Allegro CL (except for the modifications to find-package) is given below and is in the public domain. It can be used by any CL vendor to augment their implementation to behave as this document suggests. find-package should be modified according to the description just above -- trying to resolve a name as relative if the name does not itself name a package.
Note that you should not use leading dots in package names when using hierarchical packages.
Even without the modifications to cl:find-package, authors need not avoid using relative package names, but the ability to reuse relative package names is restricted. The following example illustrates this:
Consider a module foo which is composed of the my.foo.bar and my.foo.baz packages. In the code for each of these packages there are relative package references, ..bar and ..baz.
Implementations that have the new cl:find-package would have on their
*features*list the symbol
:relative-package-names. Then, in the foo module, there would be definitions of the my.foo.bar and my.foo.baz packages like so:(defpackage :my.foo.bar #-relative-package-names (:nicknames #:..bar) ...) (defpackage :my.foo.baz #-relative-package-names (:nicknames #:..baz) ...)
Then, in a
#-relative-package-namesimplementation, the symbol
my.foo.bar:blamwould be visible from my.foo.baz as
..bar:blam, just as it would from a
So, even without the implementation of the augmented find-package, one can still write CL code that will work in both types of implementations, but ..bar and ..baz are now used, so you cannot also have otherpack.foo.bar and otherpack.foo.baz and use ..bar and ..baz as relative names. (The point of hierarchical packages, of course, is to allow reusing relative package names.)
Starting in Allegro CL 6.0, Franz Inc. typically puts newly created packages under the following top-level names:
The use of these top-level names as packages in applications might run into problems with Allegro CL 6.0 and future versions. Note that all current package names (such as excl, system etc.) will also be used.
To facilitate using hierarchical packages, we introduce several new functions, other than the changed find-package: excl::relative-package-name-to-package, package-parent and package-children. The source code for these functions is also given below.
These functions are documented below with their implementation.
;; The following source code is in the public domain. ;; Provided "as is" with no warranty of any kind. ;; Use at your own risk. (pushnew :relative-package-names *features*) (defun relative-package-name-to-package (name) ;; Given a package name, a string, do a relative package name lookup. ;; ;; It is intended that this function will be called from find-package. ;; In Allegro, find-package calls package-name-to-package, and the latter ;; function calls this function when it does not find the package. ;; ;; Because this function is called via the reader, we want it to be as ;; fast as possible. (declare (optimize speed)) (flet ((relative-to (package name) (if* (string= "" name) then package else (package-name-to-package (concatenate 'simple-string (package-name package) "." name)))) (find-non-dot (name) (do* ((len (length name)) (i 0 (1+ i))) ((= i len) nil) (declare (fixnum len i)) (when (char/= #\. (schar name i)) (return i))))) (when (char= #\. (schar (simple-string name) 0)) (let* ((last-dot-position (or (find-non-dot name) (length name))) (n-dots last-dot-position) (name (subseq name last-dot-position))) (cond ((= 1 n-dots) ;; relative to current package (relative-to *package* name)) (t ;; relative to our (- n-dots 1)'th parent (let ((p *package*) tmp) (dotimes (i (1- n-dots)) (when (not (setq tmp (package-parent p))) (error "The parent of ~a does not exist." p)) (setq p tmp)) (relative-to p name)))))))) (defun package-parent (package-specifier) ;; Given package-specifier, a package, symbol or string, return the ;; parent package. If there is not a parent, signal an error. ;; ;; Because this function is called via the reader, we want it to be as ;; fast as possible. (declare (optimize speed)) (flet ((find-last-dot (name) (do* ((len (1- (length name))) (i len (1- i))) ((= i -1) nil) (declare (fixnum len i)) (when (char= #\. (schar name i)) (return i))))) (let* ((child (cond ((packagep package-specifier) (package-name package-specifier)) ((symbolp package-specifier) (symbol-name package-specifier)) ((stringp package-specifier) package-specifier) (t (error "Illegal package specifier: ~s." package-specifier)))) (dot-position (find-last-dot child))) (cond (dot-position (let ((parent (subseq child 0 dot-position))) (or (package-name-to-package parent) (error "The parent of ~a does not exist." child)))) (t (error "There is no parent of ~a." child)))))) (defun package-children (package-specifier &key (recurse t)) ;; Given package-specifier, a package, symbol or string, return all the ;; packages which are in the hierarchy "under" the given package. If ;; :recurse is nil, then only return the immediate children of the ;; package. ;; ;; While this function is not called via the reader, we do want it to be ;; fast. (declare (optimize speed)) (let ((res ()) (parent (cond ((packagep package-specifier) (package-name package-specifier)) ((symbolp package-specifier) (symbol-name package-specifier)) ((stringp package-specifier) package-specifier) (t (error "Illegal package specifier: ~s." package-specifier))))) (labels ((string-prefix-p (prefix string) ;; Return length of `prefix' if `string' starts with `prefix'. ;; We don't use `search' because it does much more than we need ;; and this version is about 10x faster than calling `search'. (let ((prefix-len (length prefix)) (seq-len (length string))) (declare (fixnum prefix-len seq-len)) (when (>= prefix-len seq-len) (return-from string-prefix-p nil)) (do* ((i 0 (1+ i))) ((= i prefix-len) prefix-len) (declare (fixnum i)) (when (not (char= (schar prefix i) (schar string i))) (return nil))))) (test-package (package-name package) (let ((prefix (string-prefix-p (concatenate 'simple-string parent ".") package-name))) (cond (recurse (when prefix (pushnew package res))) (t (when (and prefix (not (find #\. package-name :start prefix))) (pushnew package res))))))) ;; In Allegro, list-all-packages calls `sort', so use an internal ;; method to get the package names. #+allegro (maphash #'test-package *package-names*) #-allegro (dolist (package (list-all-packages)) (funcall #'test-package (package-name package) package)) res)))
The following test code can be used to check a hierarchical package
implementation. You must use the Allegro CL test harness, documented
in the test-harness.htm. The test harness is loaded
(require :tester) form.
;; The following source code is in the public domain. ;; Provided "as is" with no warranty of any kind. ;; Use at your own risk. (eval-when (compile eval load) (require :tester)) (defpackage :package-tests (:use #:common-lisp #:excl #:util.test) (:import-from #:excl #:package-children) (:import-from #:excl #:package-parent)) (in-package :package-tests) (defpackage :package-tests.a) (defpackage :package-tests.a.b) (defpackage :package-tests.a.b.c) (defpackage :package-tests.a.b.c.d) (defpackage :package-tests.a.b.c.d.e) (defpackage :package-tests.a.b.c.d.f) (defpackage :package-tests.a.b.c.e) (defpackage :package-tests.a.b.c.f) (defpackage :package-tests.a.b.d) (defpackage :package-tests.a.b.e) (defpackage :package-tests.a.c) (defpackage :package-tests.a.d) (defpackage :package-tests.b) (defpackage :package-tests.c) (defpackage :package-tests.d) (defpackage :package-tests-foo.bar.baz) (defpackage :package-tests-foo.bar.baz.wham) (defun do-package-tests () (test t (progn #+relative-package-names t #-relative-package-names nil) :test #'eq) ;;;; test package-children (test '("package-tests.a" "package-tests.b" "package-tests.c" "package-tests.d") (sort (mapcar #'package-name (package-children :package-tests :recurse nil)) #'string<) :test #'equal) (test '("package-tests.a" "package-tests.a.b" "package-tests.a.b.c" "package-tests.a.b.c.d" "package-tests.a.b.c.d.e" "package-tests.a.b.c.d.f" "package-tests.a.b.c.e" "package-tests.a.b.c.f" "package-tests.a.b.d" "package-tests.a.b.e" "package-tests.a.c" "package-tests.a.d" "package-tests.b" "package-tests.c" "package-tests.d") (sort (mapcar #'package-name (package-children :package-tests)) #'string<) :test #'equal) (test '("package-tests.a.b.c.d" "package-tests.a.b.c.d.e" "package-tests.a.b.c.d.f" "package-tests.a.b.c.e" "package-tests.a.b.c.f") (sort (mapcar #'package-name (package-children :package-tests.a.b.c)) #'string<) :test #'equal) (test '("package-tests.a.b.c.d" "package-tests.a.b.c.e" "package-tests.a.b.c.f") (sort (mapcar #'package-name (package-children :package-tests.a.b.c :recurse nil)) #'string<) :test #'equal) (test '("package-tests.a.b.c.d.e" "package-tests.a.b.c.d.f") (sort (mapcar #'package-name (package-children :package-tests.a.b.c.d)) #'string<) :test #'equal) (test '("package-tests.a.b.c.d.e" "package-tests.a.b.c.d.f") (sort (mapcar #'package-name (package-children :package-tests.a.b.c.d :recurse nil)) #'string<) :test #'equal) (test '() (package-children :package-tests.b) :test #'equal) (test '() (package-children :package-tests.c) :test #'equal) (test '() (package-children :package-tests.d) :test #'equal) ;;;; test package-parent (test (find-package :package-tests) (package-parent :package-tests.a)) (test (find-package :package-tests.a) (package-parent :package-tests.a.b)) (test (find-package :package-tests.a.b) (package-parent :package-tests.a.b.c)) (test (find-package :package-tests.a.b.c) (package-parent :package-tests.a.b.c.d)) (test (find-package :package-tests.a.b.c.d) (package-parent :package-tests.a.b.c.d.e)) (test (find-package :package-tests.a.b.c.d) (package-parent :package-tests.a.b.c.d.f)) (test (find-package :package-tests.a.b.c) (package-parent :package-tests.a.b.c.e)) (test (find-package :package-tests.a.b.c) (package-parent :package-tests.a.b.c.f)) (test (find-package :package-tests.a.b) (package-parent :package-tests.a.b.d)) (test (find-package :package-tests.a.b) (package-parent :package-tests.a.b.e)) (test (find-package :package-tests.a) (package-parent :package-tests.a.c)) (test (find-package :package-tests.a) (package-parent :package-tests.a.d)) (test (find-package :package-tests) (package-parent :package-tests.b)) (test (find-package :package-tests) (package-parent :package-tests.c)) (test (find-package :package-tests) (package-parent :package-tests.d)) (test-error (package-parent :package-tests)) (test-error (package-parent :package-tests-foo.bar.baz)) (test-error (package-parent :package-tests-foo.bar)) (test-error (package-parent :package-tests-foo)) ;;;; test find-package (dolist (item '((:package-tests.a :package-tests.a ".") (:package-tests :package-tests.a "..") (:package-tests.b :package-tests.a "..b") (:package-tests.c :package-tests.a "..c") (:package-tests.d :package-tests.a "..d") (:package-tests.a.b :package-tests.b "..a.b") (:package-tests :package-tests.a.b "...") (:package-tests.b :package-tests.a.b "...b") (:package-tests.a.b.c.d.f :package-tests.a.b.c.d "...c.d.f") (:package-tests :package-tests.a.b.c.d ".....") (:package-tests.b :package-tests.a.b.c.d ".....b") (:package-tests.a.b.c.d :package-tests.a.b.c.d ".") (:package-tests.a.b.c :package-tests.a.b.c ".") (:package-tests.a.b :package-tests.a.b "."))) (test (symbol-name (first item)) (let* ((*package* (find-package (second item))) (p (find-package (third item)))) (cond (p (package-name p)) (t (error "could not find package ~s." (third item))))))) (test-error (find-package "..")) (test-error (find-package "...")) (test-error (find-package "....")) (test-error (find-package "....foo")) (let ((*package* (find-package :package-tests.b))) (test-error (find-package "...")))) (let ((*test-errors* 0) (*test-successes* 0) (*test-unexpected-failures* 0)) (format t "Beginning package tests...~%") (do-package-tests) (format t "Completed package tests.~%") (format t "** Successes: ~s~%" *test-successes*) (format t "** Errors: ~s~%" *test-errors*) (format t "** Unexpected failures: ~s~%" *test-unexpected-failures*))
In addition to the hierarchical packages named in Section 2.3 Package prefixes reserved by Allegro CL, the following packages used by Allegro CL are of direct importance to the user. Note that all nicknames are not listed in every case. Use package-nicknames applied to a package to see the complete list. The first nickname listed in each case is the principal nickname.
Some of these packages may not exist in a standard Allegro CL image until a fasl file containing the functionality associated with the package is loaded. In most cases, the loading is automatic when the package is referenced. Thus
causes cltl1.fasl to be loaded from the bundle.
||Socket interface functionality. See socket.htm.||No||Autoloaded|
||aclwin302||Functionality from Allegro CL 3.0.2 kept in 6.x for backward compatibility.||Yes||
Exists in Windows and Unix. In Unix, do
In Unix, symbols having to do with graphics have no function definition. Functionality that is Windows-specific generates an error when called in Unix.
||the MOP extension to CLOS (CLOS functionality is in common-lisp).||Yes||Always present in an image.|
||Some symbols removed from the Common Lisp standard by X3J13.||No||Functionality named by symbols in this package is out of date and use should be avoided. Autoloaded.|
||common-graphics||Common Graphics windows functionality.||Yes||Windows only. Always present in an image with the IDE.|
||cg-user||User environment in the IDE||No||Windows only. Uses aclwin, excl, cg, cltl1, cl, ide. Always present in an image with the IDE.|
||cl||Standard CL symbols.||Yes||Always present in an image.|
|User environment.||No||Uses cl and excl. Always present in an image.|
||comp||Symbols naming functionality associated with the compiler. See compiling.htm.||Yes||Autoloaded.|
||xref||Symbols naming functionality associated with the cross referencer. See cross-reference.htm.||Yes||Autoloaded.|
||Symbols naming functionality associated with the DDE interface on Windows. See dde.htm||No||Autoloaded.|
||Symbols naming functionality associated with defsystem. See defsystem.htm||Yes||Autoloaded.|
||db||Symbols naming functionality associated with the debugger. See debugging.htm.||Yes||Autoloaded.|
||excl||General extensions to Common Lisp||Yes||Always present in an image.|
||ff||Symbols naming functionality associated with the foreign functions facility. See foreign-functions.htm.||Yes||Autoloaded.|
||Package for compiler labels and some CLOS names.||No||Always present in an image.|
||Integrated Development Environment functionality.||Yes||Windows only. Always present in an image with the IDE.|
||Symbols naming functionality associated with the inspector. See inspector.htm.||Yes||Autoloaded.|
||Standard CL package.||No||Always present in an image.|
||Symbols naming functionality associated with multiprocessing. See multiprocessing.htm.||Yes||Autoloaded.|
||prof||Symbols naming functionality associated with the runtime analyzer. See runtime-analyzer.htm.||Yes||Autoloaded.|
||sys, si||System functionality and internals.||Yes||Always present in an image.|
||tpl||Symbols naming functionality associated with the top level. See top-level.htm.||Yes||Always present in an image.|
When you start up Allegro CL on UNIX or without the Integrated
Development Environment on Windows, you are in the
common-lisp-user package. At the start, there are
no symbols in the
common-lisp-user package, but the
are used, so external symbols from those packages are available to the
user package. When you start the Integrated
Development Environment (Windows only) you are in the
common-lisp package contains only those symbols
specified in the ANSI CL specification. Some of the capabilities of
standard Common Lisp functions have been extended, but they can all be
used in the way specified in ANSI CL. The extensions are not portable,
of course. See implementation.htm for
more information on extensions to standard Common Lisp
With that caveat, if you use the common-lisp package only, you will have portable code that can with greatest ease be ported to Common Lisp systems other than Allegro CL.
A number of symbols were removed from the Common Lisp standard by
the X3J13 committee. We have maintained many of these symbols in the
cltl1 package, for the purpose of providing
contain many of the extensions in Allegro CL. Two packages in earlier
versions on UNIX (4.3.x and earlier),
stream, have been merged with
starting in version 5.0. Both
franz are nicknames of
excl is also the principal
nickname of the
excl package to ensure that name is
*print-nickname* is true.
top-level package contains symbols used by
the top level. Note that some of these symbols have the same names as
symbols in the
common-lisp package (for example,
Therefore, we recommend that a package using the
common-lisp package not use (in the sense of use-package) the
Packages can have (usually shorter) nicknames, which can be used in
place of the full names. Symbols unavailable in the current package
are printed (during, e.g., tracing) with package qualifiers. Allegro
CL allows you to specify whether you want the (non-nickname) package
name as the qualifier or the principal nickname as the qualifier. The
*print-nickname* controls whether the printer
uses the full name or the principal nickname of a package (if true,
the principal nickname is used, if
package name is used). Note that certain utilities (e.g. apropos and the debugger) bind this
variable to true and so always use the nickname.
The principal nickname of some of the packages of interest to users
are listed next (
nil means no defined
Table 2: Package Nicknames
Principal Nickname (
Other Nickname (some nicknames may not be listed)
Package nicknames can be found with the Common Lisp function
returns a list of the nicknames of its argument, with the principal
one first. Sometimes, you may wish to use a nickname of an Allegro CL
package as the name of your own package. (E.g. some users would like
to have their own package named
db, perhaps for
database functionality, but
db is a nickname of the
debugger package.) You can change the nicknames of
a package with rename-package.
You must do it in a without-package-locks form, however, because
of package locking described just below.
Packages have two kinds of locks as an extension in Allegro CL. The package-lock protects a package from changes in its structure (its use list, its exported symbols, etc.). The package-definition-lock protects the symbols in the package from new or changed uses as the name of a function, macro, structure, or type.
Tracing and advice are not affected by either type of package locking.
When the function package-lock returns true when applied to a package, we say the package is package-locked. When a package is package-locked, the system will signal an error of type package-locked-error when code is executed that tries to:
The list is exhaustive. Note that intern and delete-package cannot
signal a package-locked-error. The function package-lock applied to a package object (but
not a symbol or string naming a package) returns true if the package
is locked and returns
nil if it is not
locked. Setf can be used with package-lock to lock or unlock a package.
A package is package-definition-locked if the function package-definition-lock (whose argument must be a package object, not a package name) returns true when applied to the package. When a package is package-definition-locked, the system will signal an error when code is executed that attempts any of the following actions on a symbol homed in the package:
Function names that are lists are also protected if the important
symbol (usually the cadr, e.g. border in
border)) in the list is in the definition-locked package. We
repeat here the definition of package-definition-lock because it describes
how the lock can be circumvented.
nilas package is or is not definition-locked. package must be a package object (it cannot be a symbol or a string). setf may be used with this function to definition-lock or unlock a package.
Even if a package is package-definition-locked, no error will be signaled when
- the value of
- the violation is dynamically inside the body of a call to the macro without-package-locks;
- the list returned by applying package-implementation-packages to the value of
*package*contains the home package of the symbol being operated on. Implementation packages are defined just below. Note that unless you have specified a list of implementation packages for a package that does not include the package itself (which would be unusual), no error will be signaled when
*package*is the home package of the symbol being operated on.
If a violation is encountered while compiling a file, a warning is signaled rather than an error. If the resulting fasl file is loaded, an error will then be signaled.
Allegro CL allows a package to have a list of associated packages
(called implementation packages). No warning or error will be
signaled for a definition or redefinition in one package when the
*package* is an
implementation package of that package. Both defpackage and make-package have been extended to accept an
argument and the setfable function package-implementation-packages accesses that
list of packages.
The value of the implementation-packages argument
to make-package should be a
list of strings naming packages. The defpackage form should contain a subform which
is a list whose first element is
:implementation-packages and whose remaining
elements are strings naming the desired packages (as shown in the
example below). When unspecified, the list of implementation packages
defaults to a list containing the string naming the package being
defined. The implementation-packages argument is
not standard Common Lisp. You may wish to conditionalize it in
portable code, as shown next.
(defpackage :mypack #+allegro (:implementation-packages "MYPACK" "MYPACK-2") ; other options as desired )
:implementation-packages option will only be
read by Allegro CL. Note that since we specified a value, we had to
include "MYPACK" as well as "MYPACK-2" in order to
allow symbols whose home package is
mypack to be
redefined without warning or error while the value of
*package* is the
Note that implementation packages protects against warnings and errors for package definition locks only. Package locks (the distinction is described above) are not affected.
Here is an example. Suppose we define two packages: foo and
bar. "BAR" is on the
:implementation-packages list for
foo, but "FOO" is not on the
:implementation-packages list for
bar. Both packages are definition-locked.
(defpackage :foo (:implementation-packages "FOO" "BAR")) (defpackage :bar) (setf (package-definition-lock (find-package :foo)) t) (setf (package-definition-lock (find-package :bar)) t)
Consider the following two files. The first starts with
(in-package :bar) and defines a function on
foo::mysym. The second starts with
(in-package :foo) and defines a function on
bar::my-other-sym. Compiling or
loading the first file signals no warning or error, since the bar
package is an implementation package for the foo package. The second
signals a warning on compilation and an error on loading because the
foo package is not an implementation package for the
;; File # 1 ;; Compiling or loading this file will not signal a warning ;; (for compilation) ;; or an error (for loading) even if the FOO package is ;; definition locked, ;; because the BAR package is an implementation package of ;; the FOO package. (in-package :bar) (defun foo::mysym (a b ) (+ a b)) ;; File # 2 ;; Compiling or loading this file will signal a warning ;; (for compilation) ;; or an error (for loading) if the BAR package is definition ;; locked, because ;; the FOO package is not an implementation package ;; of the BAR package. (in-package :foo) (defun bar::my-other-sym (c) (sqrt c))
The following script shows what happens when you try to perform a
protected action on a package-locked package. Here we try to export
USER(3): (export 'excl:: *debug-enclose-printer-errors* (find-package :excl)) Error: #<The EXCL package> is locked against changes by EXPORT. [condition type: PACKAGE-LOCKED-ERROR] Restart actions (select using :continue): 0: Allow EXPORT to modify #<The EXCL package>. [1c] USER(4):
The next script shows what happens when you try to define a
function on a symbol in a package-definition-locked package. We try to
define a function on the symbol
excl:*read-init-files*. We chose this admittedly
strange example to make clear that a symbol need not already have a
function definition (the symbol in question does not) in order for an
error to be signaled.
USER(18): (defun excl:*read-init-files* nil nil) Error: Attempt to make a FUNCTION definition for the name EXCL:*READ-INIT-FILES*. This name is in the EXCL package and defining it is a violation for portable programs. The package EXCL has PACKAGE-LOCK-DEFINITIONS set, which causes the system to check for this violation. [condition type: PACKAGE-LOCKED-ERROR] Restart actions (select using :continue): 0: Set the FUNCTION definition of the name EXCL:*READ-INIT-FILES* anyway. [1c] USER(19):
In each case, the error has condition type package-locked-error and in each case the error is continuable. By entering :continue 0, the requested action (exporting the symbol or defining the function) will take place.
Note however that package locking is in place for a reason: changing a system-supplied package or defining (or particularly redefining) a function on a symbol in a system-supplied package can cause Lisp to fail because assumptions about the package are violated.
Obviously there are times when changing a package or the definition on a symbol is the right thing to do. If, for example, we instruct you to make some change (say, export a symbol accidentally left off an export list), we are guaranteeing that doing so will not have adverse consequences.
*enable-package-locked-errors* and macro
without-package-locks can be
used to prevent package-locked-errors (of either type -- ordinary
locks and definition locks) without actually unlocking a package.
*enable-package-locked-errors* is true,
executing code that violates package-locking or
package-definition-locking will signal errors and compiling such code
will signal warnings as described above. When it is
nil, such code will execute without
package-locked-errors or compile-time warnings.
The macro without-package-locks, which takes one or more
forms as its arguments, evaluates those forms with
For symbols in the
common-lisp package, all of
the actions prevented by package locking and package definition
locking are explicitly restricted by the ANSI specification (see
sections 18.104.22.168.2 and 22.214.171.124.2.1). The
common-lisp package is locked and definition locked
as are a number of Allegro CL packages, including
aclmop aclwin (Windows only) clos cltl1 common-graphics (Windows only) common-lisp compiler cross-reference debugger defsystem excl excl.scm foreign-functions inspect lep multiprocessing profiler system top-level
common-lisp package, the restrictions of both
package-locks and package-lock-definitions locks are compliant with
the ANSI standard. Other system-provided packages in Allegro CL are
also locked, for the same reasons that the
common-lisp package is locked.
Writers of application packages may want to lock their packages as
well, especially if the package may be used by other packages written
later. Package locks can detect inadvertent name collisions before
they cause program failures. The following forms will package-lock and
package-definition-lock the package
foo. The same
nil instead of
t, unlock the package.
(setf (excl:package-lock (find-package :foo)) t) (setf (excl:package-definition-lock (find-package :foo)) t)
Copyright (c) 1998-2009, Franz Inc. Oakland, CA., USA. All rights reserved.
Documentation for Allegro CL version 8.1. This page was not revised from the 8.0 page.
|Allegro CL version 8.1|
Unrevised from 8.0 to 8.1.