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47 lines
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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: Section 1.6</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="01_ebb.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="01_.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="01_g.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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1.6 Language Extensions</H2> <P>
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<P>
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A language extension is any documented <A REL=DEFINITION HREF="26_glo_i.htm#implementation-defined"><I>implementation-defined</I></A> behavior of a <A REL=DEFINITION HREF="26_glo_d.htm#defined_name"><I>defined name</I></A> in this standard that varies from the behavior described in this standard, or a documented consequence of a situation that the standard specifies as undefined, unspecified, or extendable by the implementation. For example, if this standard says that ``the results are unspecified,'' an extension would be to specify the results. <P>
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If the correct behavior of a program depends on the results provided by an extension, only implementations with the same extension will execute the program correctly. Note that such a program might be non-conforming. Also, if this standard says that ``an implementation may be extended,'' a conforming, but possibly non-portable, program can be written using an extension. <P>
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An implementation can have extensions, provided they do not alter the behavior of conforming code and provided they are not explicitly prohibited by this standard. <P>
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<P>
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The term ``extension'' refers only to extensions available upon startup. An implementation is free to allow or prohibit redefinition of an extension. <P>
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The following list contains specific guidance to implementations concerning certain types of extensions. <P><DL><P>
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<DT><B>Extra return values</B> <P><DD>
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An implementation must return exactly the number of return values specified by this standard unless the standard specifically indicates otherwise. <P>
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<DT><B>Unsolicited messages</B> <P><DD>
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<P>
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No output can be produced by a function other than that specified in the standard or due to the signaling of <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>conditions</I></A> detected by the function. <P>
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Unsolicited output, such as garbage collection notifications and autoload heralds, should not go directly to the <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A> that is the value of a <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A> variable defined in this standard, but can go indirectly to <A REL=DEFINITION HREF="26_glo_t.htm#terminal_iSLo"><I>terminal I/O</I></A> by using a <A REL=DEFINITION HREF="26_glo_s.htm#synonym_stream"><I>synonym stream</I></A> to <A REL=DEFINITION HREF="v_termin.htm#STterminal-ioST"><B>*terminal-io*</B></A>. <P>
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Progress reports from such functions as <A REL=DEFINITION HREF="f_load.htm#load"><B>load</B></A> and <A REL=DEFINITION HREF="f_cmp.htm#compile"><B>compile</B></A> are considered solicited, and are not covered by this prohibition. <P>
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<P>
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<DT><B>Implementation of macros and special forms</B> <P><DD>
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<P>
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<A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>Macros</I></A> and <A REL=DEFINITION HREF="26_glo_s.htm#special_operator"><I>special operators</I></A> defined in this standard must not be <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A>. <P>
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<P></DL><P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss227.htm">MACRO-AS-FUNCTION:DISALLOW</A><LI> <A REL=CHILD HREF="../Issues/iss357.htm">UNSOLICITED-MESSAGES:NOT-TO-SYSTEM-USER-STREAMS</A><LI> <A REL=CHILD HREF="../Issues/iss156.htm">EXTRA-RETURN-VALUES:NO</A><LI> <A REL=CHILD HREF="../Issues/iss154.htm">EXTENSIONS-POSITION:DOCUMENTATION</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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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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