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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Issue PACKAGE-DELETION Writeup</TITLE>
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<H2>Issue PACKAGE-DELETION Writeup</H2>
<PRE><B>Forum:</B> Cleanup<P>
<B>Issue:</B> <A HREF="iss253.htm">PACKAGE-DELETION</A><P>
<B>References:</B> Packages (pp171-192), <A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> (p184), <A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> (p76)<P>
<B>Category:</B> ADDITION<P>
<B>Edit history:</B> 30-Sep-88, Version 1 by Pitman<P>
01-Oct-88, Version 2 by Pitman<P>
04-Oct-88, Version 3 by Pitman<P>
(<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>provide</B></A> for correctable errors in some cases)<P>
07-Oct-88, Version 4 by JonL<P>
21-Nov-88, Version 5 by Masinter<P>
<P>
<P>
<B>Problem Description:<P>
</B><P>
There is no way to get rid of a package in Common Lisp.<P>
<P>
This absence makes interactive development work tricky in some<P>
implementations. If a package is accidentally built incorrectly, the<P>
user must either rename the package to another package or start over<P>
by reloading his program in a fresh lisp image.<P>
<P>
Some programs need to create and destroy packages at runtime.<P>
Without such a facility, some clumsy combination of <A REL=DEFINITION HREF="../Body/f_rn_pkg.htm#rename-package"><B>RENAME-PACKAGE</B></A>,<P>
<A REL=DEFINITION HREF="../Body/f_uninte.htm#unintern"><B>UNINTERN</B></A>, and <A REL=DEFINITION HREF="../Body/f_unuse_.htm#unuse-package"><B>UNUSE-PACKAGE</B></A> is usually made to work. However, it is<P>
easy for a casual programmer to forget to undo some of the <P>
bookkeeping, leading to unwanted effects.<P>
<P>
<B>Proposal (PACKAGE-DELETION:NEW-FUNCTION):<P>
</B><P>
Introduce the function <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A>, described as follows:<P>
<P>
<A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> package [Function]<P>
<P>
Deletes <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A> from all package system data structures. <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A> may<P>
be either a package or the name of a package.<P>
<P>
If <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A> is a package name (i.e., not type <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A>) which does not<P>
currently name a package, a correctable error is signalled. If<P>
continued, no deletion action is attempted. Instead, <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A><P>
immediately returns <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>.<P>
<P>
If <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A> is a package object (i.e., an object of type <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A>)<P>
which has already been deleted, no error is signalled and no further<P>
deletion action is attempted. Instead, <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> immediately<P>
returns <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>.<P>
<P>
If the designated package is used by other packages, a correctable<P>
error is signalled. If continued, the effect of <A REL=DEFINITION HREF="../Body/f_unuse_.htm#unuse-package"><B>UNUSE-PACKAGE</B></A> is<P>
done to remove any dependencies, causing its external symbols to stop<P>
being accessible to those packages. Once this is done, <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A><P>
goes on to delete the package just as it would had there been no <P>
packages that used it.<P>
<P>
After this operation completes, the contents of the <A REL=DEFINITION HREF="../Body/f_symb_3.htm#symbol-package"><B>symbol-package</B></A> <P>
slot of any symbol homed in the deleted package is unspecified; for <P>
those symbols not homed in that package, the contents remain unchanged.<P>
Except for this, symbols in the deleted package are not modified in<P>
any other way. <P>
<P>
The effect of <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> is that the name and<P>
nicknames of the designated package cease to be recognized package<P>
names. The package object is still a package -- <A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> is true<P>
of it -- but <A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> will return <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>. The effect of any other <P>
package operation on <A REL=DEFINITION HREF="../Body/t_pkg.htm#package"><B>PACKAGE</B></A> once it has been deleted is undefined.<P>
In particular, <A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A>, <A REL=DEFINITION HREF="../Body/f_intern.htm#intern"><B>INTERN</B></A> and other functions that<P>
look for a symbol name in a package will have unspecified results if<P>
called with <A REL=DEFINITION HREF="../Body/v_pkg.htm#STpackageST"><B>*PACKAGE*</B></A> bound to the deleted package or with the<P>
deleted package as an argument.<P>
<P>
<A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> returns T if the deletion attempt was successful<P>
and <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> otherwise.<P>
<P>
<B>Examples:<P>
</B><P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> *FOO-PACKAGE* (<A REL=DEFINITION HREF="../Body/f_mk_pkg.htm#make-package"><B>MAKE-PACKAGE</B></A> &quot;FOO&quot; :USE <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>))<P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> *FOO-SYMBOL* (<A REL=DEFINITION HREF="../Body/f_intern.htm#intern"><B>INTERN</B></A> &quot;FOO&quot; *FOO-PACKAGE*))<P>
(<A REL=DEFINITION HREF="../Body/f_export.htm#export"><B>EXPORT</B></A> *FOO-SYMBOL* *FOO-PACKAGE*)<P>
<P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> *BAR-PACKAGE* (<A REL=DEFINITION HREF="../Body/f_mk_pkg.htm#make-package"><B>MAKE-PACKAGE</B></A> &quot;BAR&quot; :USE '(&quot;FOO&quot;)))<P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> *BAR-SYMBOL* (<A REL=DEFINITION HREF="../Body/f_intern.htm#intern"><B>INTERN</B></A> &quot;BAR&quot; *BAR-PACKAGE*))<P>
(<A REL=DEFINITION HREF="../Body/f_export.htm#export"><B>EXPORT</B></A> *FOO-SYMBOL* *BAR-PACKAGE*)<P>
(<A REL=DEFINITION HREF="../Body/f_export.htm#export"><B>EXPORT</B></A> *BAR-SYMBOL* *BAR-PACKAGE*)<P>
<P>
(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>SETQ</B></A> *BAZ-PACKAGE* (<A REL=DEFINITION HREF="../Body/f_mk_pkg.htm#make-package"><B>MAKE-PACKAGE</B></A> &quot;BAZ&quot; :USE '(&quot;BAR&quot;)))<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_symb_3.htm#symbol-package"><B>SYMBOL-PACKAGE</B></A> *FOO-SYMBOL*) =&gt; #&lt;Package &quot;FOO&quot;&gt;<P>
(<A REL=DEFINITION HREF="../Body/f_symb_3.htm#symbol-package"><B>SYMBOL-PACKAGE</B></A> *BAR-SYMBOL*) =&gt; #&lt;Package &quot;BAR&quot;&gt;<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#prin1-to-string"><B>PRIN1-TO-STRING</B></A> *FOO-SYMBOL*) =&gt; &quot;FOO:FOO&quot;<P>
(<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#prin1-to-string"><B>PRIN1-TO-STRING</B></A> *BAR-SYMBOL*) =&gt; &quot;BAR:BAR&quot;<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;FOO&quot; *BAR-PACKAGE*) =&gt; FOO:FOO, :EXTERNAL<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;FOO&quot; *BAZ-PACKAGE*) =&gt; FOO:FOO, :INHERITED<P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;BAR&quot; *BAZ-PACKAGE*) =&gt; BAR:BAR, :INHERITED<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *FOO-PACKAGE*) =&gt; T<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *BAR-PACKAGE*) =&gt; T<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *BAZ-PACKAGE*) =&gt; T<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *FOO-PACKAGE*) =&gt; &quot;FOO&quot;<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *BAR-PACKAGE*) =&gt; &quot;BAR&quot;<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *BAZ-PACKAGE*) =&gt; &quot;BAZ&quot;<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *FOO-PACKAGE*) =&gt; ()<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *BAR-PACKAGE*) =&gt; (#&lt;Package FOO&gt;)<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *BAZ-PACKAGE*) =&gt; (#&lt;Package BAR&gt;)<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *FOO-PACKAGE*) =&gt; (#&lt;Package BAR&gt;)<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *BAR-PACKAGE*) =&gt; (#&lt;Package BAZ&gt;)<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *BAZ-PACKAGE*) =&gt; ()<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> *BAR-PACKAGE*)<P>
Error: Package BAZ uses package BAR.<P>
If continued, BAZ will be made to <A REL=DEFINITION HREF="../Body/f_unuse_.htm#unuse-package"><B>unuse-package</B></A> BAR,<P>
and then BAR will be deleted.<P>
Type :CONTINUE to continue.<P>
Debug&gt; :CONTINUE<P>
=&gt; T<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_symb_3.htm#symbol-package"><B>SYMBOL-PACKAGE</B></A> *FOO-SYMBOL*) =&gt; #&lt;Package &quot;FOO&quot;&gt;<P>
(<A REL=DEFINITION HREF="../Body/f_symb_3.htm#symbol-package"><B>SYMBOL-PACKAGE</B></A> *BAR-SYMBOL*) is unspecified<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#prin1-to-string"><B>PRIN1-TO-STRING</B></A> *FOO-SYMBOL*) =&gt; &quot;FOO:FOO&quot;<P>
(<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#prin1-to-string"><B>PRIN1-TO-STRING</B></A> *BAR-SYMBOL*) is unspecified<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;FOO&quot; *BAR-PACKAGE*) is undefined<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;FOO&quot; *BAZ-PACKAGE*) =&gt; <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>, <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A><P>
(<A REL=DEFINITION HREF="../Body/f_find_s.htm#find-symbol"><B>FIND-SYMBOL</B></A> &quot;BAR&quot; *BAZ-PACKAGE*) =&gt; <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>, <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A><P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *FOO-PACKAGE*) =&gt; T<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *BAR-PACKAGE*) =&gt; T<P>
(<A REL=DEFINITION HREF="../Body/f_pkgp.htm#packagep"><B>PACKAGEP</B></A> *BAZ-PACKAGE*) =&gt; T<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *FOO-PACKAGE*) =&gt; &quot;FOO&quot;<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *BAR-PACKAGE*) =&gt; <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A><P>
(<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A> *BAZ-PACKAGE*) =&gt; &quot;BAZ&quot;<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *FOO-PACKAGE*) =&gt; ()<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *BAR-PACKAGE*) is undefined<P>
(<A REL=DEFINITION HREF="../Body/f_pkg_us.htm#package-use-list"><B>PACKAGE-USE-LIST</B></A> *BAZ-PACKAGE*) =&gt; ()<P>
<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *FOO-PACKAGE*) =&gt; ()<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *BAR-PACKAGE*) is undefined<P>
(<A REL=DEFINITION HREF="../Body/f_pkg__1.htm#package-used-by-list"><B>PACKAGE-USED-BY-LIST</B></A> *BAZ-PACKAGE*) =&gt; ()<P>
<P>
<B>Rationale:<P>
</B><P>
This facility corrects the deficiency described in the problem description.<P>
<P>
<B>Current Practice:<P>
</B><P>
Symbolics has a function PKG-KILL which satisfies the proposed behavior<P>
except that an error is not signalled if the package is used.<P>
When a package is killed by PKG-KILL, the home package of all symbols<P>
in that package are left undisturbed (i.e., local symbols pointing to<P>
the killed package); this aspect is compatible with the stated proposal.<P>
<P>
Procyon Common Lisp has a function called <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A> already. It<P>
returns the name of the package so deleted (as a string). [Perhaps it also<P>
differs in the correctability of the errors it signals?]<P>
<P>
Lucid Common Lisp implements <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A>, except that the continuation<P>
option for a name that doesn't name a package is different.<P>
<P>
<B>Cost to Implementors:<P>
</B><P>
The cost of providing this facility is probably small.<P>
<P>
<B>Cost to Users:<P>
</B><P>
Very slight to none. This change is essentially compatible.<P>
<P>
Some code which cached packages in variables might have to be slightly<P>
more cautious, but experience in the Symbolics implementation suggests<P>
that it's really the responsibility of the person doing the <A REL=DEFINITION HREF="../Body/f_del_pk.htm#delete-package"><B>DELETE-PACKAGE</B></A><P>
to take care of worrying about the effects of having deleted the package:<P>
normal programs need not bother testing a package for validity (using<P>
<A REL=DEFINITION HREF="../Body/f_pkg_na.htm#package-name"><B>PACKAGE-NAME</B></A>) before using it.<P>
<P>
<B>Cost of Non-Adoption:<P>
</B><P>
Getting rid of a package would continue to be difficult to do portably.<P>
<P>
<B>Benefits:<P>
</B><P>
Better control of storage usage would be available portably.<P>
<P>
<B>Aesthetics:<P>
</B><P>
No significant effect.<P>
<P>
<B>Discussion:<P>
</B><P>
This was discussed as part of a larger bulk issue of how to undo all<P>
sorts of definitions. Since that proposal has not gone anywhere <P>
(perhaps bogged down under its own weight), this subtopic has been<P>
broken off for separate discussion.<P>
<P>
Note that if a symbol's package component is modified as a result<P>
of being &quot;unintern'd&quot; from a delete packaged, then it is unspecified<P>
as to how it will be printed.<P>
<P>
</PRE>
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