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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 IN-PACKAGE-FUNCTIONALITY Writeup</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="../Issues/iss194_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss195.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss196_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue IN-PACKAGE-FUNCTIONALITY Writeup</H2>
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<PRE><B>Status:</B> proposal MAR89-X3J13 passed, as amended, Mar 89 X3J13<P>
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<B>Issue:</B> <A HREF="iss195.htm">IN-PACKAGE-FUNCTIONALITY</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> (p182-183)<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit history:</B> 07-Jul-88, Version 1 by Pitman<P>
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7-Oct-88, Version 2 by Masinter (discussion)<P>
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8-Dec-88, Version 3 by Masinter<P>
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12-Dec-88, Version 4 by Masinter<P>
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20-Jan-89, Version 5 by Loosemore<P>
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30-Jan-89, Version 6 by Loosemore<P>
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10-Mar-89, Version 7 by Loosemore<P>
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15-Mar-89, Version 8 by Masinter (add back SELECT-ONLY)<P>
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9-Apr-89, Verison 9 by Masinter, as amended Mar 89 X3J13,<P>
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and discussion updated.<P>
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<P>
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Related-Issues: <A REL=DEFINITION HREF="../Body/m_defpkg.htm#defpackage"><B>DEFPACKAGE</B></A> (passed)<P>
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<A HREF="iss063.htm">COMPILE-FILE-SYMBOL-HANDLING</A><P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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There are two typical uses for <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> -- to define/create a package<P>
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and to select a package. The fact that these two purposes have been<P>
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given to the same function has led to reduced error checking.<P>
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<P>
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A more general problem is that the "Put In Seven Extremely Randoms" <P>
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convention described in CLtL is now recognized by many people as being<P>
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unsatisfactory for both package definition and package selection.<P>
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The <A REL=DEFINITION HREF="../Body/m_defpkg.htm#defpackage"><B>DEFPACKAGE</B></A> macro provides a much cleaner mechanism for package<P>
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definition, but there is still a need for a convenient way to select<P>
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a package that has well-defined compilation semantics.<P>
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<P>
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<P>
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<B>Proposal (IN-PACKAGE-FUNCTIONALITY:MAR89-X3J13):<P>
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</B><P>
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Change <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> from a function to a macro:<P>
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<P>
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<A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> name [macro]<P>
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<P>
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This macro causes <A REL=DEFINITION HREF="../Body/v_pkg.htm#STpackageST"><B>*PACKAGE*</B></A> to be set to the package named NAME,<P>
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which must be a symbol or string. An error is signalled if the<P>
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package does not already exist. Everything this macro does is also<P>
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performed at compile time if the call appears at top-level.<P>
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<P>
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Remove the second paragraph of section 11.7 in CLtL. (This includes<P>
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the requirement for special compile-time treatment of the various<P>
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package functions.)<P>
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<P>
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Rationale:<P>
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<P>
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This could allow improved error checking and modularity, with only<P>
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minimal loss of functionality.<P>
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<P>
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Making <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> a macro rather than a function means that there<P>
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is no need to <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>require</B></A> <A REL=DEFINITION HREF="../Body/f_cmp_fi.htm#compile-file"><B>COMPILE-FILE</B></A> to handle it specially. Since<P>
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<A REL=DEFINITION HREF="../Body/m_defpkg.htm#defpackage"><B>DEFPACKAGE</B></A> is also defined to side-effect the compilation environment,<P>
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there is no need to <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>require</B></A> any of the package functions to be treated<P>
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specially by the compiler.<P>
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<P>
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The language in section 11.7 of CLtL puts the burden on<P>
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implementations of ensuring that all symbols in a file which is<P>
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compiled and loaded end up in the same package that they would if the<P>
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source file were loaded interpretively. No implementation can<P>
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possibly meet this requirement because, in general, the runtime<P>
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behavior of the program cannot be predicted by the compiler.<P>
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<P>
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Current Practice:<P>
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<P>
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Probably no one implements this behavior exactly since it's an <P>
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incompatible change to CLtL.<P>
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<P>
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Cost to Implementors:<P>
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<P>
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The SELECT-PACKAGE macro can be implemented trivially by using <P>
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<A REL=DEFINITION HREF="../Body/s_eval_w.htm#eval-when"><B>EVAL-WHEN</B></A> in its expansion:<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/m_defmac.htm#defmacro"><B>defmacro</B></A> select-package (name)<P>
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`(<A REL=DEFINITION HREF="../Body/s_eval_w.htm#eval-when"><B>eval-when</B></A> (<A REL=DEFINITION HREF="../Body/f_eval.htm#eval"><B>eval</B></A> <A REL=DEFINITION HREF="../Body/f_cmp.htm#compile"><B>compile</B></A> <A REL=DEFINITION HREF="../Body/f_load.htm#load"><B>load</B></A>)<P>
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(<A REL=DEFINITION HREF="../Body/s_setq.htm#setq"><B>setq</B></A> <A REL=DEFINITION HREF="../Body/v_pkg.htm#STpackageST"><B>*package*</B></A><P>
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(<A REL=DEFINITION HREF="../Body/a_or.htm#or"><B>or</B></A> (<A REL=DEFINITION HREF="../Body/f_find_p.htm#find-package"><B>find-package</B></A> ',name)<P>
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(<A REL=DEFINITION HREF="../Body/a_error.htm#error"><B>error</B></A> "Package ~s does <A REL=DEFINITION HREF="../Body/a_not.htm#not"><B>not</B></A> exist." ',name)))))<P>
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<P>
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The changes required to <A REL=DEFINITION HREF="../Body/f_cmp_fi.htm#compile-file"><B>COMPILE-FILE</B></A> to remove the magic treatment<P>
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of the package functions are also likely to be small.<P>
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<P>
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Cost to Users:<P>
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<P>
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In most cases, minor syntactic changes to some files would be<P>
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necessary. Programmers that are now using the "Put In Seven<P>
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Extremely Randoms" convention will probably find it straightforward<P>
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to convert their code to do a <A REL=DEFINITION HREF="../Body/m_defpkg.htm#defpackage"><B>DEFPACKAGE</B></A> followed by a <P>
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SELECT-PACKAGE.<P>
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<P>
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Cost of Non-Adoption:<P>
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<P>
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The specification of <A REL=DEFINITION HREF="../Body/f_cmp_fi.htm#compile-file"><B>COMPILE-FILE</B></A> will be much more difficult to<P>
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understand.<P>
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<P>
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The <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> will <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>require</B></A> compilers to solve the halting problem.<P>
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<P>
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Benefits:<P>
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<P>
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Modular package declarations would be encouraged and errors due<P>
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to demand-creation of packages would be easier to detect.<P>
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<P>
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The specification of <A REL=DEFINITION HREF="../Body/f_cmp_fi.htm#compile-file"><B>COMPILE-FILE</B></A> will be simplified.<P>
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<P>
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There will be a clear statement of the requirements for program<P>
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conformance, as relating to usage of packages.<P>
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<P>
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Aesthetics:<P>
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<P>
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The fact that <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> is currently ambiguous about intent (whether<P>
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the package should exist already or not) is clearly not aesthetic.<P>
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Removing it can't be any worse.<P>
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<P>
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The fact that the currently stated requirements for handling of<P>
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the package functions by the compiler are not implementable is<P>
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clearly not aesthetic.<P>
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<B>Discussion:<P>
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</B><P>
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The dual use of <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> has not been helpful and is confusing.<P>
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<P>
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This is an incompatible change.<P>
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<P>
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KMP's notes of the Mar 89 X3J13:<P>
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<P>
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On Tuesday, we took a straw poll.<P>
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0 opposed both proposals.<P>
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15 liked NEW-MACRO.<P>
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7 liked SELECT-ONLY.<P>
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``Keeping <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> makes no difference to compatibility.'' --Moon<P>
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Pitman moved to amend this to say "deprecate" instead of remove.<P>
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The motion to amend failed 3-N.<P>
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The NEW-MACRO proposal passed unamended 12-4.<P>
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<P>
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On Thursday, Aaron Larson and JonL asked that the issue be reconsidered.<P>
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The motion to reconsider passed N-1.<P>
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There was a motion to rename the SELECT-PACKAGE which we'd voted in to<P>
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<A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> -- so that the compatible syntax (<A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A> "FOO") would work<P>
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in CLtL and ANSI CL.<P>
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Steele requested verbal clarification that we were not trying to solve<P>
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the ``dusty file'' problem but rather to make it possible to write new code<P>
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that worked in old and new situations -- it was agreed that this was a<P>
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correct characterization of the proposal.<P>
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JonL's amendment passed 13-1.<P>
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Then the amended proposal was voted in 14-0.<P>
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<P>
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The net effect is that NEW-MACRO passed with the name of SELECT-PACKAGE<P>
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changed to <A REL=DEFINITION HREF="../Body/m_in_pkg.htm#in-package"><B>IN-PACKAGE</B></A>.<P>
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<P>
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<P>
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</PRE>
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<HR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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