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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 REQUIRE-PATHNAME-DEFAULTS 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/iss295_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss296.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss297_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue REQUIRE-PATHNAME-DEFAULTS Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss296.htm">REQUIRE-PATHNAME-DEFAULTS</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/v_module.htm#STmodulesST"><B>*MODULES*</B></A>, <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A>, <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A>, pp 188-191<P>
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<A REL=DEFINITION HREF="../Body/f_load.htm#load"><B>LOAD</B></A>, pp 426-427<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit history:</B> Version 1 by Pierson 9/13/88<P>
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Version 2 by Pierson 9/19/88, change <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> stuff per comments<P>
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Version 3 by Pierson 10/17/88, remove <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> locaction specs.<P>
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Version 4 by Pierson 10/31/88, remove from language<P>
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Version 5 by Pierson 11/15/88, cleanup, fix discussion<P>
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Version 6 by Pierson 12/9/88, remove <A REL=DEFINITION HREF="../Body/v_module.htm#STmodulesST"><B>*MODULES*</B></A> as well<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> are a dual-purpose pair of functions that attempt<P>
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to <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>provide</B></A> multi-file Common Lisp programs with a single mechanism to<P>
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detect and correct incorrect load sequences. These functions were<P>
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also designed to be used for general file inclusion in Common Lisp.<P>
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Unfortunately, the file loading feature of <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> is specified such<P>
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that it is inherently non-portable and environment dependent.<P>
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<P>
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<B>Proposal (REQUIRE-PATHNAME-DEFAULTS:ELIMINATE):<P>
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</B><P>
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Remove <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A>, <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A>, and <A REL=DEFINITION HREF="../Body/v_module.htm#STmodulesST"><B>*MODULES*</B></A> from the Common Lisp <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A>.<P>
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<P>
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<B>Test Cases/Examples:<P>
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</B><P>
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(<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> 'fft)<P>
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<P>
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Would not be Common Lisp.<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> 'fft)<P>
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<P>
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Would not be Common Lisp.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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The file loading feature of <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> is non-portable. The remaining<P>
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functionality of <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> (pushing and testing <A REL=DEFINITION HREF="../Body/v_module.htm#STmodulesST"><B>*MODULES*</B></A>)<P>
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can easily be implemented by user code. Since some implementations<P>
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will retain the automatic module loading features of <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> and some<P>
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won't, use of <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> will almost always make code less portable.<P>
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<P>
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<B>Current practice:<P>
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</B><P>
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All implementations currently support some sort of file loading via<P>
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single-argument <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A>. In general, the Lisp Machine implementations<P>
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invoke the system module building/loading facility while the Unix<P>
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implementations simply try to load a file in the current directory.<P>
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<P>
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<B>Cost to Implementors:<P>
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</B><P>
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Implementations will have to move <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> to their package<P>
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for implementation extensions and change their documentation to<P>
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indicate that <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> are non-standard. This is a fairly<P>
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small change.<P>
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<P>
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<B>Cost to Users:<P>
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</B><P>
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Non-portable programs that rely on <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> will probably<P>
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be unaffected since implementations will probably maintain their<P>
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existing functionality. Since the current behavior is decidedly<P>
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non-portable, portable programs have to aviod or special-case <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A><P>
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and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> anyway.<P>
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<P>
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<B>Cost of non-Adoption:<P>
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</B><P>
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<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> will continue as impediments to portability.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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The non-portability of <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> will be made obvious.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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This simplifies the language by removing an environment-dependent<P>
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feature. <P>
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<P>
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<B>Discussion:<P>
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</B><P>
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The cleanup committee tried to come up with a proposal to restrict<P>
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<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> to the portable subset of their functionality.<P>
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This failed because several implementors objected that it compelled<P>
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them to significantly reduce the functionality they provided users in<P>
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order to create a trivial feature which any user could easily write<P>
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for herself.<P>
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<P>
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Fahlman, Gregor, Grey, Loosemore, Moon, Pierson, Pitman, Steele, and<P>
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Zacharias have expressed support for removing <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> from<P>
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the language, at least as the lesser of several evils.<P>
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<P>
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JonL would much rather see <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> remain in the language<P>
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as a safety net behind any implementation-specific system building<P>
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facility. Pierson likes the safety net idea, but doesn't think it's<P>
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workable without forbidding <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> from loading files.<P>
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<P>
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Pitman suggested that <A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> should be depricated rather<P>
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than removed entirely. Pierson agrees, but notes that Larry wants us<P>
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to deal with deprication versus elimination as a separate global topic.<P>
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<P>
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Several people have expressed a desire not to break existing user<P>
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code. If accepted, this proposal should not break existing code<P>
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because all implementations are expected to retain their current<P>
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<A REL=DEFINITION HREF="../Body/f_provid.htm#provide"><B>PROVIDE</B></A> and <A REL=DEFINITION HREF="../Body/f_provid.htm#require"><B>REQUIRE</B></A> functionality as an extension to Common Lisp.<P>
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<P>
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</PRE>
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