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80 lines
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<H2>Issue COPY-SYMBOL-COPY-PLIST Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss087.htm">COPY-SYMBOL-COPY-PLIST</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/f_cp_sym.htm#copy-symbol"><B>COPY-SYMBOL</B></A> (p 169), <A REL=DEFINITION HREF="../Body/f_cp_lis.htm#copy-list"><B>COPY-LIST</B></A> (p 268), <A REL=DEFINITION HREF="../Body/f_cp_tre.htm#copy-tree"><B>COPY-TREE</B></A> (p<P>
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269).<P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> 10-Jan-89, Version 1 by Margolin<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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The description of <A REL=DEFINITION HREF="../Body/f_cp_sym.htm#copy-symbol"><B>COPY-SYMBOL</B></A>, where the COPY-PROPS optional argument<P>
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is non-NIL, says that a copy of the property list is used as the new<P>
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symbol's property list. However, there are several ways in which a list<P>
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may be copied, most notably <A REL=DEFINITION HREF="../Body/f_cp_lis.htm#copy-list"><B>COPY-LIST</B></A> and <A REL=DEFINITION HREF="../Body/f_cp_tre.htm#copy-tree"><B>COPY-TREE</B></A>, and the description<P>
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doesn't say which mechanism should be used.<P>
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<P>
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Proposal (<A HREF="iss087.htm">COPY-SYMBOL-COPY-PLIST:COPY-LIST</A>)<P>
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<P>
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Clarify that when <A REL=DEFINITION HREF="../Body/f_cp_sym.htm#copy-symbol"><B>COPY-SYMBOL</B></A> copies the property list of the symbol, it<P>
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is as if (<A REL=DEFINITION HREF="../Body/f_cp_lis.htm#copy-list"><B>COPY-LIST</B></A> (<A REL=DEFINITION HREF="../Body/f_symb_4.htm#symbol-plist"><B>SYMBOL-PLIST</B></A> sym)) were used as the new symbol's<P>
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property list.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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<A REL=DEFINITION HREF="../Body/f_cp_lis.htm#copy-list"><B>COPY-LIST</B></A> is the simplest list-copying primitive. The result of this<P>
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copy is that <A REL=DEFINITION HREF="../Body/f_get.htm#get"><B>GET</B></A> returns <A REL=DEFINITION HREF="../Body/a_eql.htm#eql"><B>EQL</B></A> results for the two symbols until one of<P>
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the property lists is altered, but altering either of the property lists<P>
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doesn't affect the other. This is current practice in the<P>
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implementations I tested, and probably what most users assume.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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Symbolics Genera and Sun Common Lisp currently implement this. I<P>
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suspect most others do, too.<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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Little or none.<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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None unless they've been assuming some other type of copy.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Less ambiguity.<P>
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<P>
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<B>Aesthetics:<P>
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</B><P>
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Well, I like it.<P>
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<P>
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</PRE>
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