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<TITLE>CLHS: Issue DEFTYPE-KEY 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/iss121_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss122.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss123_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue DEFTYPE-KEY Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss122.htm">DEFTYPE-KEY</A><P>
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<P>
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<B>References:</B> CLtL p.50<P>
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<P>
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Related issues: <A HREF="iss109.htm">DEFSTRUCT-CONSTRUCTOR-KEY-MIXTURE</A><P>
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<P>
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<B>Category:</B> CLARIFICATION/ADDITION<P>
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<P>
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<B>Edit history:</B> 29-Apr-90, Version 1 by Moon<P>
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30-Apr-90, Version 2 by Moon (update current practice)<P>
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4-May-90, Version 3 by Moon (update from comment received)<P>
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9-May-90, Version 4 by Moon (revise according to comments<P>
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received. Specifically, remove references to<P>
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<A REL=DEFINITION HREF="../Body/03_dd.htm#AMenvironment"><B>&ENVIRONMENT</B></A>, take no stand on destructuring, and<P>
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correct the current practice.)<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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CLtL p.50 only mentions <A REL=DEFINITION HREF="../Body/03_da.htm#AMoptional"><B>&OPTIONAL</B></A> and <A REL=DEFINITION HREF="../Body/03_da.htm#AMrest"><B>&REST</B></A> as allowed lambda-list<P>
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keywords in <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A>. It doesn't say whether <A REL=DEFINITION HREF="../Body/03_da.htm#AMkey"><B>&KEY</B></A> is allowed too.<P>
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<P>
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This is Symbolics issue #18.<P>
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<P>
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<B>Proposal (DEFTYPE-KEY:ALLOW):<P>
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</B><P>
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Allow <A REL=DEFINITION HREF="../Body/03_da.htm#AMoptional"><B>&OPTIONAL</B></A>, <A REL=DEFINITION HREF="../Body/03_da.htm#AMrest"><B>&REST</B></A>, <A REL=DEFINITION HREF="../Body/03_da.htm#AMkey"><B>&KEY</B></A>, <A REL=DEFINITION HREF="../Body/03_da.htm#AMallow-other-keys"><B>&ALLOW-OTHER-KEYS</B></A>, and <A REL=DEFINITION HREF="../Body/03_da.htm#AMaux"><B>&AUX</B></A> in the<P>
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lambda-list of <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A>.<P>
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<P>
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Clarify that unsupplied keyword arguments default to *, not <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>, the same<P>
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as unsupplied optional arguments, if no initform is specified in the<P>
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lambda-list. <A REL=DEFINITION HREF="../Body/03_da.htm#AMaux"><B>&AUX</B></A> parameters are initialized to <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> if no initform is<P>
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specified.<P>
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<P>
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<B>Examples:<P>
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</B><P>
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(<A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>deftype</B></A> xarray (<A REL=DEFINITION HREF="../Body/03_da.htm#AMkey"><B>&key</B></A> dimensions (rank '* rank-p) element-type)<P>
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(<A REL=DEFINITION HREF="../Body/m_check_.htm#check-type"><B>check-type</B></A> rank (<A REL=DEFINITION HREF="../Body/a_or.htm#or"><B>or</B></A> (<A REL=DEFINITION HREF="../Body/a_member.htm#member"><B>member</B></A> *) (<A REL=DEFINITION HREF="../Body/t_intege.htm#integer"><B>integer</B></A> 0 *)))<P>
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(<A REL=DEFINITION HREF="../Body/m_check_.htm#check-type"><B>check-type</B></A> dimensions (<A REL=DEFINITION HREF="../Body/a_or.htm#or"><B>or</B></A> (<A REL=DEFINITION HREF="../Body/a_member.htm#member"><B>member</B></A> *) <A REL=DEFINITION HREF="../Body/a_list.htm#list"><B>list</B></A>))<P>
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`(<A REL=DEFINITION HREF="../Body/t_array.htm#array"><B>array</B></A> ,element-type<P>
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,(<A REL=DEFINITION HREF="../Body/s_if.htm#if"><B>if</B></A> rank-p rank dimensions)))<P>
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<P>
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(<A REL=DEFINITION HREF="../Body/m_check_.htm#check-type"><B>check-type</B></A> z (xarray :rank 2 :element-type <A REL=DEFINITION HREF="../Body/t_short_.htm#double-float"><B>double-float</B></A>))<P>
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<P>
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(define-presentation-type command (<A REL=DEFINITION HREF="../Body/03_da.htm#AMkey"><B>&key</B></A> (command-table *command-table*))<P>
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....)<P>
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<P>
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define-presentation-type is similar to <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>deftype</B></A> but defines some<P>
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additional information about use of the type in user interfaces.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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Type specifiers with keyword arguments are used extensively in CLIM<P>
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and CLIM-based applications.<P>
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<P>
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<A REL=DEFINITION HREF="../Body/03_da.htm#AMaux"><B>&AUX</B></A> is allowed just for completeness.<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 8.0 supports the proposal.<P>
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Lucid 3.0.1 signals an error (<A REL=DEFINITION HREF="../Body/03_da.htm#AMkey"><B>&KEY</B></A> not allowed) for this example.<P>
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Franz Allegro CL 3.1.beta.22 supports the proposal.<P>
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Other implementations were not surveyed.<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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Should be small since this simply makes <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> support the same<P>
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lambda-list keywords as <A REL=DEFINITION HREF="../Body/m_defun.htm#defun"><B>DEFUN</B></A> and <A REL=DEFINITION HREF="../Body/a_lambda.htm#lambda"><B>LAMBDA</B></A> (which suggests an<P>
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implementation technique of inserting '* where an initform is not<P>
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specified for an &optional or &keyword argument and then making a<P>
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function that is applied to the <A REL=DEFINITION HREF="../Body/f_car_c.htm#cdr"><B>cdr</B></A> of the type specifier).<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.<P>
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<P>
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<B>Cost of non-adoption:<P>
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</B><P>
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CLIM will not fit into Common Lisp as well. <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> will be less<P>
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consistent with the rest of the language.<P>
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<P>
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<B>Performance impact:<P>
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</B><P>
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None.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Cost of non-adoption will not be incurred.<P>
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<P>
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<B>Esthetics:<P>
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</B><P>
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<A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> will be consistent with <A REL=DEFINITION HREF="../Body/m_defun.htm#defun"><B>DEFUN</B></A>, eliminating an arbitrary<P>
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restriction.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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There has been some discussion about whether <A REL=DEFINITION HREF="../Body/m_deftp.htm#deftype"><B>DEFTYPE</B></A> supports<P>
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destructuring. It seems that CLtL pages 50 and 146 may contradict<P>
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each other on this point. This issue explicitly does not address<P>
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the question of destructuring.<P>
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</PRE>
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