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<H2>Issue EXTRA-RETURN-VALUES Writeup</H2>
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<PRE>Version 6 (not shown here) is what passed.<P>
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It was modified by amendment to strike everything in the <P>
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proposal section except for the first paragraph. <P>
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v6 is the one that passed.<P>
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-kmp (Aug 89)<P>
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<P>
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-----<P>
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<B>Issue:</B> <A HREF="iss156.htm">EXTRA-RETURN-VALUES</A><P>
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<B>References:</B> Chapter 1, Section 1.5, Working draft of <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A><P>
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<B>Category:</B> Clarification<P>
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<B>Edit history:</B> 8-JAN-89, Version 1 by Masinter<P>
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3-FEB-89, Version 2 by Chapman<P>
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10-MAR-89, Version 3 by Chapman<P>
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30-MAY-89, Version 4 by Pierson<P>
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20-JUN-89, Version 5 by Chapman<P>
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<P>
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<P>
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Problem: Is it OK to return extra values from Common Lisp functions?<P>
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<P>
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Proposal: <A HREF="iss156.htm">EXTRA-RETURN-VALUES:NO</A><P>
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<P>
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A function that is specified by the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> must return EXACTLY the number <P>
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of return values specified by the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A>. <P>
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<P>
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The following functions are explicited permitted to have additional<P>
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return values: <P>
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<P>
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<A REL=DEFINITION HREF="../Body/f_gethas.htm#gethash"><B>gethash</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_remhas.htm#remhash"><B>remhash</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_set_ma.htm#get-macro-character"><B>get-macro-character</B></A> <P>
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<A REL=DEFINITION HREF="../Body/f_set__1.htm#get-dispatch-macro-character"><B>get-dispatch-macro-character</B></A><P>
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read<P>
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<A REL=DEFINITION HREF="../Body/f_rd_rd.htm#read-preserving-whitespace"><B>read-preserving-whitespace</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_rd_del.htm#read-delimited-list"><B>read-delimited-list</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_rd_lin.htm#read-line"><B>read-line</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_rd_cha.htm#read-char"><B>read-char</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_unrd_c.htm#unread-char"><B>unread-char</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_peek_c.htm#peek-char"><B>peek-char</B></A><P>
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listen<P>
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<A REL=DEFINITION HREF="../Body/f_rd_c_1.htm#read-char-no-hang"><B>read-char-no-hang</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_rd_fro.htm#read-from-string"><B>read-from-string</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_parse_.htm#parse-integer"><B>parse-integer</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_rd_by.htm#read-byte"><B>read-byte</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#write-to-string"><B>write-to-string</B></A><P>
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prin1-to-string<P>
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<A REL=DEFINITION HREF="../Body/f_wr_to_.htm#princ-to-string"><B>princ-to-string</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_wr_stg.htm#write-string"><B>write-string</B></A><P>
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format<P>
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<A REL=DEFINITION HREF="../Body/f_y_or_n.htm#y-or-n-p"><B>y-or-n-p</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_y_or_n.htm#yes-or-no-p"><B>yes-or-no-p</B></A><P>
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open<P>
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<A REL=DEFINITION HREF="../Body/f_rn_fil.htm#rename-file"><B>rename-file</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_probe_.htm#probe-file"><B>probe-file</B></A><P>
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directory<P>
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<A REL=DEFINITION HREF="../Body/m_tracec.htm#trace"><B>trace</B></A><P>
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<A REL=DEFINITION HREF="../Body/m_tracec.htm#untrace"><B>untrace</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_apropo.htm#apropos-list"><B>apropos-list</B></A><P>
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describe <P>
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<P>
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<P>
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<P>
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<B>Rationale:<P>
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</B> <P>
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The reason is that additional arguments are visible to otherwise<P>
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portable programs. For instance, (<A REL=DEFINITION HREF="../Body/s_multip.htm#multiple-value-call"><B>multiple-value-call</B></A> #'cons (floor x<P>
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y)) looks portable, but it will try to pass the wrong number of<P>
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arguments to <A REL=DEFINITION HREF="../Body/a_cons.htm#cons"><B>CONS</B></A> if <A REL=DEFINITION HREF="../Body/f_floorc.htm#floor"><B>FLOOR</B></A> returns an extra value.<P>
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<P>
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The order of the above list is by page number in CLtL.<P>
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<P>
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<B>Current Practice:<P>
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</B> <P>
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At least one implementation returns extra values for certain functions<P>
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not currently specified to return those values.<P>
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<P>
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<B>Adoption Cost:<P>
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</B> <P>
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Implementations and their associated documentation that now contain <P>
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functions that return extra values will have to change.<P>
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<P>
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<B>Benefits:<P>
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</B> <P>
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Programs will potentially become more portable.<P>
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<P>
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<B>Conversion Cost:<P>
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</B> <P>
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See Adoption Cost.<P>
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<P>
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<B>Aesthetics:<P>
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</B> <P>
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None.<P>
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<P>
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<B>Discussion:<P>
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</B>Pierson created the original list, Moon revised the list.<P>
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<P>
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Moon says:<P>
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"The ones that I care the most about are <A REL=DEFINITION HREF="../Body/f_gethas.htm#gethash"><B>gethash</B></A> and <A REL=DEFINITION HREF="../Body/f_rd_lin.htm#read-line"><B>read-line</B></A>."<P>
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</PRE>
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