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89 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: Function SET-DISPATCH-MACRO-CHARACTER...</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="f_rdta_1.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_reader.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_set_ma.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="set-dispatch-macro-character"><A NAME="get-dispatch-macro-character"><I>Function</I> <B>SET-DISPATCH-MACRO-CHARACTER, GET-DISPATCH-MACRO-CHARACTER</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>get-dispatch-macro-character</B> <I>disp-char sub-char <TT>&optional</TT> readtable</I> => <I>function</I><P>
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<P>
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<B>set-dispatch-macro-character</B> <I>disp-char sub-char new-function <TT>&optional</TT> readtable</I> => <I><A REL=DEFINITION HREF="a_t.htm#t"><B>t</B></A></I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>disp-char</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A>. <P>
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<I>sub-char</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A>. <P>
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<I>readtable</I>---a <A REL=DEFINITION HREF="26_glo_r.htm#readtable_designator"><I>readtable designator</I></A>. The default is the <A REL=DEFINITION HREF="26_glo_c.htm#current_readtable"><I>current readtable</I></A>. <P>
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<I>function</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#function_designator"><I>function designator</I></A> or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>new-function</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#function_designator"><I>function designator</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#set-dispatch-macro-character"><B>set-dispatch-macro-character</B></A> causes <I>new-function</I> to be called when <I>disp-char</I> followed by <I>sub-char</I> is read. If <I>sub-char</I> is a lowercase letter, it is converted to its uppercase equivalent. It is an error if <I>sub-char</I> is one of the ten decimal digits. <P>
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<A REL=DEFINITION HREF="#set-dispatch-macro-character"><B>set-dispatch-macro-character</B></A> installs a <I>new-function</I> to be called when a particular <A REL=DEFINITION HREF="26_glo_d.htm#dispatching_macro_character"><I>dispatching macro character</I></A> pair is read. <I>New-function</I> is installed as the dispatch function to be called when <I>readtable</I> is in use and when <I>disp-char</I> is followed by <I>sub-char</I>. <P>
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For more information about how the <I>new-function</I> is invoked, see <A REL=CHILD HREF="02_add.htm">Section 2.1.4.4 (Macro Characters)</A>. <P>
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<A REL=DEFINITION HREF="#get-dispatch-macro-character"><B>get-dispatch-macro-character</B></A> retrieves the dispatch function associated with <I>disp-char</I> and <I>sub-char</I> in <I>readtable</I>. <P>
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<A REL=DEFINITION HREF="#get-dispatch-macro-character"><B>get-dispatch-macro-character</B></A> returns the macro-character function for <I>sub-char</I> under <I>disp-char</I>, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> if there is no function associated with <I>sub-char</I>. If <I>sub-char</I> is a decimal digit, <A REL=DEFINITION HREF="#get-dispatch-macro-character"><B>get-dispatch-macro-character</B></A> returns <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(get-dispatch-macro-character #\# #\{) => NIL
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(set-dispatch-macro-character #\# #\{ ;dispatch on #{
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#'(lambda(s c n)
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(let ((list (read s nil (values) t))) ;list is object after #n{
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(when (consp list) ;return nth element of list
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(unless (and n (< 0 n (length list))) (setq n 0))
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(setq list (nth n list)))
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list))) => T
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#{(1 2 3 4) => 1
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#3{(0 1 2 3) => 3
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#{123 => 123
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</PRE>
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</TT> If it is desired that <TT>#$</TT><I>foo</I><TT></TT> : as if it were <TT>(dollars </TT><I>foo</I><TT>)</TT>. <P>
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<PRE>
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(defun |#$-reader| (stream subchar arg)
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(declare (ignore subchar arg))
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(list 'dollars (read stream t nil t))) => |#$-reader|
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(set-dispatch-macro-character #\# #\$ #'|#$-reader|) => T
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</PRE>
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</TT> <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=CHILD HREF="02_add.htm">Section 2.1.4.4 (Macro Characters)</A> <P>
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<P><B>Side Effects:</B><P>
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<P>
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The <I>readtable</I> is modified. <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_rdtabl.htm#STreadtableST"><B>*readtable*</B></A>. <P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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For either function, an error is signaled if <I>disp-char</I> is not a <A REL=DEFINITION HREF="26_glo_d.htm#dispatching_macro_character"><I>dispatching macro character</I></A> in <I>readtable</I>. <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_rdtabl.htm#STreadtableST"><B>*readtable*</B></A> <P>
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<P><B>Notes:</B><P>
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It is necessary to use <A REL=DEFINITION HREF="f_mk_dis.htm#make-dispatch-macro-character"><B>make-dispatch-macro-character</B></A> to set up the dispatch character before specifying its sub-characters. <P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss184.htm">GET-MACRO-CHARACTER-READTABLE:NIL-STANDARD</A><P></UL><HR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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