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59 lines
6.3 KiB
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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: Function DESCRIBE</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="f_apropo.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_enviro.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_desc_1.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="describe"><I>Function</I> <B>DESCRIBE</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>describe</B> <I>object <TT>&optional</TT> stream</I> => <I><I><no values></I></I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>object</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>stream</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#output"><I>output</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#stream_designator"><I>stream designator</I></A>. The default is <A REL=DEFINITION HREF="26_glo_s.htm#standard_output"><I>standard output</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#describe"><B>describe</B></A> displays information about <I>object</I> to <I>stream</I>. <P>
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For example, <A REL=DEFINITION HREF="#describe"><B>describe</B></A> of a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> might show the <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>'s value, its definition, and each of its properties. <A REL=DEFINITION HREF="#describe"><B>describe</B></A> of a <A REL=DEFINITION HREF="26_glo_f.htm#float"><I>float</I></A> might show the number's internal representation in a way that is useful for tracking down round-off errors. In all cases, however, the nature and format of the output of <A REL=DEFINITION HREF="#describe"><B>describe</B></A> is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A>. <P>
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<A REL=DEFINITION HREF="#describe"><B>describe</B></A> can describe something that it finds inside the <I>object</I>; in such cases, a notational device such as increased indentation or positioning in a table is typically used in order to visually distinguish such recursive descriptions from descriptions of the argument <I>object</I>. <P>
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The actual act of describing the object is implemented by <A REL=DEFINITION HREF="f_desc_1.htm#describe-object"><B>describe-object</B></A>. <A REL=DEFINITION HREF="#describe"><B>describe</B></A> exists as an interface primarily to manage argument defaulting (including conversion of arguments <A REL=DEFINITION HREF="a_t.htm#t"><B>t</B></A> and <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> into <A REL=DEFINITION HREF="26_glo_s.htm#stream"><I>stream</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A>) and to inhibit any return values from <A REL=DEFINITION HREF="f_desc_1.htm#describe-object"><B>describe-object</B></A>. <P>
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<A REL=DEFINITION HREF="#describe"><B>describe</B></A> is not intended to be an interactive function. In a <A REL=DEFINITION HREF="26_glo_c.htm#conforming_implementation"><I>conforming implementation</I></A>, <A REL=DEFINITION HREF="#describe"><B>describe</B></A> must not, by default, prompt for user input. User-defined methods for <A REL=DEFINITION HREF="f_desc_1.htm#describe-object"><B>describe-object</B></A> are likewise restricted. <P>
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<P><B>Examples:</B> None.
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<P>
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<P><B>Side Effects:</B><P>
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<P>
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Output to <A REL=DEFINITION HREF="26_glo_s.htm#standard_output"><I>standard output</I></A> or <A REL=DEFINITION HREF="26_glo_t.htm#terminal_iSLo"><I>terminal I/O</I></A>. <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_debug_.htm#STstandard-outputST"><B>*standard-output*</B></A> and <A REL=DEFINITION HREF="v_termin.htm#STterminal-ioST"><B>*terminal-io*</B></A>, methods on <A REL=DEFINITION HREF="f_desc_1.htm#describe-object"><B>describe-object</B></A> and <A REL=DEFINITION HREF="f_pr_obj.htm#print-object"><B>print-object</B></A> for <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> having user-defined <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>classes</I></A>. <P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_inspec.htm#inspect"><B>inspect</B></A>, <A REL=DEFINITION HREF="f_desc_1.htm#describe-object"><B>describe-object</B></A> <P>
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<P><B>Notes:</B> None.
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<P>
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<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/iss127.htm">DESCRIBE-INTERACTIVE:NO</A><LI> <A REL=CHILD HREF="../Issues/iss128.htm">DESCRIBE-UNDERSPECIFIED:DESCRIBE-OBJECT</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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