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69 lines
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<H2>Issue SETF-APPLY-EXPANSION Writeup</H2>
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<PRE><B>Status:</B> Proposal IGNORE-EXPANDER passed 12/91<P>
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<B>Issue:</B> <A HREF="iss303.htm">SETF-APPLY-EXPANSION</A><P>
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Reference: CLtL-II, p.127<P>
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Draft 10.156, p.5-10<P>
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<B>Category:</B> CHANGE<P>
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<B>Edit History:</B> Version 1, 12-Dec-91, Kim Barrett<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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In Draft 10.156, the description of a call to <A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A> as a place for <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> does<P>
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not include some text from CLtL. Specifically, the draft says that for a<P>
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user-defined function,<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> (<A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A> #'name a1 a2 ...) v1)<P>
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<P>
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is equivalent to<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A> #'(<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> name) v1 a1 a2 ...)<P>
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<P>
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except that the proper left-to-right evaluation order is maintained. Instead<P>
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of this, CLtL talks about <A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A> as a place in terms of the expander for the<P>
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function name as a place, saying that the last argument to the store form must<P>
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be the same as the last argument of the access call.<P>
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<P>
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<B>Proposal (SETF-APPLY-EXPANSION:IGNORE-EXPANDER):<P>
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</B> <P>
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Affirm the draft text, eliminating the mechanism prescribed by CLtL for<P>
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handling <A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A> as a place for <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A>.<P>
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<P>
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<B>Editorial impact:<P>
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</B><P>
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None. This affirms the wording in the draft.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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Implementation of the mechanism described in CLtL places some unmentioned<P>
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requirements on the <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> expander of functions that will be used with <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> of<P>
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<A REL=DEFINITION HREF="../Body/f_apply.htm#apply"><B>APPLY</B></A>. Some people consider the whole mechanism an ugly and unreliable hack.<P>
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</PRE>
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