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82 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: Issue CLOS-ERROR-CHECKING-ORDER Writeup</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="../Issues/iss049_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss050.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss051_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue CLOS-ERROR-CHECKING-ORDER Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss050.htm">CLOS-ERROR-CHECKING-ORDER</A><P>
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Reference: dpANS 12.24<P>
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Section 7.6.5 Keyword Arguments in Generic Functions and Methods<P>
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Section 7.6.6 Method Selection and Combination<P>
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<A REL=DEFINITION HREF="../Body/f_no_app.htm#no-applicable-method"><B>no-applicable-method</B></A>, p.7-47<P>
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X3J13/92-3248 David Moon comment #48<P>
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<B>Category:</B> CLARIFICATION/CHANGE<P>
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<B>Edit History:</B> Version 1, 12/13/92, Kim Barrett<P>
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<B>Status:</B> Proposal NO-APPLICABLE-METHOD-FIRST passed (10+1)-0 on<P>
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letter ballot 93-302.<P>
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<P>
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<B>Problem Description:<P>
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</B><P>
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There is no specification of the ordering between the check for<P>
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<A REL=DEFINITION HREF="../Body/f_no_app.htm#no-applicable-method"><B>no-applicable-method</B></A> and the check for unexpected keyword arguments.<P>
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Specifically, section 7.6.5 states that if a generic function is passed a<P>
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keyword argument that no applicable <A REL=DEFINITION HREF="../Body/t_method.htm#method"><B>method</B></A> accepts, an error should be<P>
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signaled, while section 7.6.6 states that if there are no applicable methods<P>
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then the generic function no-applicable-methods is called.<P>
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<P>
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<B>Proposal (CLOS-ERROR-CHECKING-ORDER:NO-APPLICABLE-METHOD-FIRST):<P>
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</B><P>
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Check for no applicable <A REL=DEFINITION HREF="../Body/t_method.htm#method"><B>method</B></A> first. Change the end of the last paragraph<P>
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of section 7.6.6 from<P>
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<P>
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If a \term{generic function} is called and no \term{methods} are<P>
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\term{applicable}, the \term{generic function} \funref{no-applicable-method}<P>
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is invoked.<P>
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<P>
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to<P>
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<P>
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If a \term{generic function} is called and no \term{methods} are<P>
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\term{applicable}, the \term{generic function} \funref{no-applicable-method}<P>
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is invoked, with the \term{results} from that call being used as the<P>
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\term{results} of the call to the original \term{generic function}. Calling<P>
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\funref{no-applicable-method} takes precedence over checking for acceptable<P>
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keyword arguments; \SeeSection{... section name for 7.6.5 ...}.<P>
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<P>
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<B>Editorial Impact:<P>
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</B><P>
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Changing or adding a couple of lines of text.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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It was clearly intended that the call to no-applicable-methods be for value,<P>
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rather than for effect. It just wasn't actually specified that way anywhere.<P>
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<P>
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Adopting the suggested order would remove an ambiguity from the specification<P>
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and would make the <A REL=DEFINITION HREF="../Body/f_no_app.htm#no-applicable-method"><B>no-applicable-method</B></A> feature a little more useful.<P>
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<P>
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</PRE>
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