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33 lines
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<TITLE>CLHS: Section 22.2.1.4</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="22_bac.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="22_ba.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="22_bae.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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22.2.1.4 Pretty Print Dispatch Tables</H2> <P>
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<P>
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A <A REL=DEFINITION HREF="26_glo_p.htm#pprint_dispatch_table"><I>pprint dispatch table</I></A> is a mapping from keys to pairs of values. Each key is a <A REL=DEFINITION HREF="26_glo_t.htm#type_specifier"><I>type specifier</I></A>. The values associated with a key are a ``function'' (specifically, 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>) and a ``numerical priority'' (specifically, a <A REL=DEFINITION HREF="t_real.htm#real"><I>real</I></A>). Basic insertion and retrieval is done based on the keys with the equality of keys being tested by <A REL=DEFINITION HREF="f_equal.htm#equal"><B>equal</B></A>. <P>
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When <A REL=DEFINITION HREF="v_pr_pre.htm#STprint-prettyST"><B>*print-pretty*</B></A> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, the <A REL=DEFINITION HREF="26_glo_c.htm#current_pprint_dispatch_table"><I>current pprint dispatch table</I></A> (in <A REL=DEFINITION HREF="v_pr_ppr.htm#STprint-pprint-dispatchST"><B>*print-pprint-dispatch*</B></A>) controls how <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> are printed. The information in this table takes precedence over all other mechanisms for specifying how to print <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A>. In particular, it has priority over user-defined <A REL=DEFINITION HREF="f_pr_obj.htm#print-object"><B>print-object</B></A> <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> because the <A REL=DEFINITION HREF="26_glo_c.htm#current_pprint_dispatch_table"><I>current pprint dispatch table</I></A> is consulted first. <P>
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The function is chosen from the <A REL=DEFINITION HREF="26_glo_c.htm#current_pprint_dispatch_table"><I>current pprint dispatch table</I></A> by finding the highest priority function that is associated with a <A REL=DEFINITION HREF="26_glo_t.htm#type_specifier"><I>type specifier</I></A> that matches the <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>; if there is more than one such function, it is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A> which is used. <P>
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However, if there is no information in the table about how to <A REL=DEFINITION HREF="26_glo_p.htm#pretty_print"><I>pretty print</I></A> a particular kind of <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>, a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> is invoked which uses <A REL=DEFINITION HREF="f_pr_obj.htm#print-object"><B>print-object</B></A> to print the <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. The value of <A REL=DEFINITION HREF="v_pr_pre.htm#STprint-prettyST"><B>*print-pretty*</B></A> is still <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> when this function is <I>called</I>, and individual methods for <A REL=DEFINITION HREF="f_pr_obj.htm#print-object"><B>print-object</B></A> might still elect to produce output in a special format conditional on the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of <A REL=DEFINITION HREF="v_pr_pre.htm#STprint-prettyST"><B>*print-pretty*</B></A>. <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss116.htm">DEFSTRUCT-PRINT-FUNCTION-AGAIN:X3J13-MAR-93</A><LI> <A REL=CHILD HREF="../Issues/iss180.htm">GENERALIZE-PRETTY-PRINTER:UNIFY</A><P></UL><HR>
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