464 lines
10 KiB
HTML
464 lines
10 KiB
HTML
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<!DOCTYPE HTML>
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<HTML LANG="en-us"
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><HEAD
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><TITLE
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>*print-readably* | Common Lisp Nova Spec</TITLE
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><META CHARSET="US-ASCII"
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><LINK REL="canonical" HREF="v_print-readably.html"
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><LINK REL="next" HREF="v_print-right-margin.html" TYPE="text/html" TITLE="*print-right-margin*"
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><LINK REL="prev" HREF="v_print-pretty.html" TYPE="text/html" TITLE="*print-pretty*"
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><LINK REL="up" HREF="22_4_Printer_Dictionary.html" TYPE="text/html" TITLE="22.4 Printer Dictionary"
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><LINK REL="start" HREF="index.html" TYPE="text/html" TITLE="Common Lisp Nova Spec"
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><META NAME="VIEWPORT" CONTENT="width=device-width, initial-scale=1.0"
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><LINK REL="STYLESHEET" HREF="dpans.css%3F3909942064.css"
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><SCRIPT SRC="dpans.js%3F3909942064"
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></SCRIPT
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><SCRIPT SRC="apropos.js%3F3909942064"
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></SCRIPT
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></HEAD
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><BODY
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><DIV
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><DIV CLASS="topnav"
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><DIV CLASS="breadcrumb"
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><SPAN CLASS="breadcrumb-item"
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><A HREF="index.html"
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>Common Lisp Nova Spec</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="22_Printer.html"
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>22. Printer</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="22_4_Printer_Dictionary.html"
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>22.4 Printer Dictionary</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="v_print-readably.html"
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>*print-readably*</A
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></SPAN
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></DIV
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><DIV CLASS="apropos"
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><DIV CLASS="apropos-io"
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><A HREF="v_print-pretty.html" CLASS="prev"
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>←</A
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><SPAN ID="apropos-label"
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>Apropos </SPAN
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><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
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><A HREF="v_print-right-margin.html" CLASS="next"
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>→</A
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></DIV
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><DIV ID="apropos-res"
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></DIV
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></DIV
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></DIV
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><DIV CLASS="matter"
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><DIV CLASS="com"
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><DIV CLASS="begincom"
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><HR
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TR
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="*print-readably*"
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></SPAN
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><SPAN CLASS="cmsy"
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>*</SPAN
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><B
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>print-readably</B
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><SPAN CLASS="cmsy"
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>*</SPAN
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Variable</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Value Type</B
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></DT
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><DD
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><P CLASS="j"
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>a <A HREF="26_1_Glossary.html#generalized_boolean"
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><EM CLASS="term"
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>generalized boolean</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Initial Value</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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>If <A HREF="v_print-readably.html" CLASS="varref"
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><B
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>*print-readably*</B
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></A
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> is <A HREF="26_1_Glossary.html#true"
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><EM CLASS="term"
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>true</EM
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></A
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>, some special rules for printing <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>objects</EM
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></A
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> go into effect. Specifically, printing any <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> <I
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>O</I
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>1</SPAN
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></SUB
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> produces a printed representation that, when seen by the <A HREF="26_1_Glossary.html#Lisp_reader"
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><EM CLASS="term"
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>Lisp reader</EM
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></A
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> while the <A HREF="26_1_Glossary.html#standard_readtable"
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><EM CLASS="term"
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>standard readtable</EM
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></A
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> is in effect, will produce an <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> <I
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>O</I
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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> that is <A HREF="26_1_Glossary.html#similar"
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><EM CLASS="term"
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>similar</EM
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></A
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> to <I
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>O</I
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>1</SPAN
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></SUB
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>. The printed representation produced might or might not be the same as the printed representation produced when <A HREF="v_print-readably.html" CLASS="varref"
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><B
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>*print-readably*</B
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></A
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> is <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>. If printing an <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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> <A HREF="26_1_Glossary.html#readably"
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><EM CLASS="term"
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>readably</EM
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></A
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> is not possible, an error of <A HREF="26_1_Glossary.html#type"
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><EM CLASS="term"
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>type</EM
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></A
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> <A HREF="t_print-not-readable.html" CLASS="typeref"
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><B
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>print-not-readable</B
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></A
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> is signaled rather than using a syntax (<I CLASS="i"
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><I
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>e.g.</I
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></I
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>, the “<CODE CLASS="f"
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>#<</CODE
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>” syntax) that would not be readable by the same <A HREF="26_1_Glossary.html#implementation"
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><EM CLASS="term"
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>implementation</EM
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></A
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>. If the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>value</EM
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></A
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> of some other <A HREF="26_1_Glossary.html#printer_control_variable"
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><EM CLASS="term"
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>printer control variable</EM
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></A
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> is such that these requirements would be violated, the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>value</EM
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></A
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> of that other <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> is ignored. </P
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><P CLASS="j"
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>Specifically, if <A HREF="v_print-readably.html" CLASS="varref"
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><B
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>*print-readably*</B
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></A
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> is <A HREF="26_1_Glossary.html#true"
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><EM CLASS="term"
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>true</EM
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></A
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>, printing proceeds as if <A HREF="v_print-escape.html" CLASS="varref"
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><B
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>*print-escape*</B
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></A
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>, <A HREF="v_print-array.html" CLASS="varref"
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><B
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>*print-array*</B
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></A
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>, and <A HREF="v_print-gensym.html" CLASS="varref"
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><B
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>*print-gensym*</B
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></A
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> were also <A HREF="26_1_Glossary.html#true"
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><EM CLASS="term"
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>true</EM
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></A
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>, and as if <A HREF="v_print-level.html" CLASS="varref"
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><B
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>*print-length*</B
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></A
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>, <A HREF="v_print-level.html" CLASS="varref"
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><B
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>*print-level*</B
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></A
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>, and <A HREF="v_print-lines.html" CLASS="varref"
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><B
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>*print-lines*</B
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></A
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> were <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>. </P
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><P CLASS="j"
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>If <A HREF="v_print-readably.html" CLASS="varref"
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><B
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>*print-readably*</B
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></A
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> is <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>, the normal rules for printing and the normal interpretations of other <A HREF="26_1_Glossary.html#printer_control_variable"
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><EM CLASS="term"
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>printer control variables</EM
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></A
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> are in effect. </P
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><P CLASS="j"
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>Individual <A HREF="26_1_Glossary.html#method"
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><EM CLASS="term"
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>methods</EM
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></A
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> for <A HREF="f_print-object.html" CLASS="funref"
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><B
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>print-object</B
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></A
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>, including user-defined <A HREF="26_1_Glossary.html#method"
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><EM CLASS="term"
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>methods</EM
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></A
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>, are responsible for implementing these requirements. </P
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><P CLASS="j"
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>If <A HREF="v_read-eval.html" CLASS="varref"
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><B
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>*read-eval*</B
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></A
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> is <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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> and <A HREF="v_print-readably.html" CLASS="varref"
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><B
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>*print-readably*</B
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></A
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> is <A HREF="26_1_Glossary.html#true"
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><EM CLASS="term"
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>true</EM
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></A
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>, any such method that would output a reference to the “<CODE CLASS="f"
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>#.</CODE
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>” <A HREF="26_1_Glossary.html#reader_macro"
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><EM CLASS="term"
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>reader macro</EM
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></A
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> will either output something else or will signal an error (as described above).</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
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><DD
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><PRE CLASS="screen"
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> (let ((x (list "a" '\a (gensym) '((a (b (c))) d e f g)))
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(*print-escape* nil)
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(*print-gensym* nil)
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(*print-level* 3)
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(*print-length* 3))
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(write x)
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(let ((*print-readably* t))
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(terpri)
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(write x)
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:done))
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<SPAN CLASS="cmr"
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>⊳</SPAN
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> (a a G4581 ((A #) D E ...))
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<SPAN CLASS="cmr"
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>⊳</SPAN
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> ("a" |a| #:G4581 ((A (B (C))) D E F G))
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<SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> :DONE
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;; This is setup code is shared between the examples
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;; of three hypothetical implementations which follow.
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(setq table (make-hash-table)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> #<HASH-TABLE EQL 0/120 32005763>
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(setf (gethash table 1) 'one) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> ONE
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(setf (gethash table 2) 'two) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> TWO
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;; Implementation A
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(let ((*print-readably* t)) (print table))
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Error: Can't print #<HASH-TABLE EQL 0/120 32005763> readably.
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;; Implementation B
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;; No standardized #S notation for hash tables is defined,
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;; but there might be an implementation-defined notation.
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(let ((*print-readably* t)) (print table))
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<SPAN CLASS="cmr"
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>⊳</SPAN
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> #S(HASH-TABLE :TEST EQL :SIZE 120 :CONTENTS (1 ONE 2 TWO))
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<SPAN CLASS="cmsy"
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||
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><SPAN CLASS="arrow"
|
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|
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>→</SPAN
|
||
|
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></SPAN
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> #<HASH-TABLE EQL 0/120 32005763>
|
||
|
|
|
||
|
|
;; Implementation C
|
||
|
|
;; Note that #. notation can only be used if *READ-EVAL* is true.
|
||
|
|
;; If *READ-EVAL* were false, this same implementation might have to
|
||
|
|
;; signal an error unless it had yet another printing strategy to fall
|
||
|
|
;; back on.
|
||
|
|
(let ((*print-readably* t)) (print table))
|
||
|
|
<SPAN CLASS="cmr"
|
||
|
|
>⊳</SPAN
|
||
|
|
> #.(LET ((HASH-TABLE (MAKE-HASH-TABLE)))
|
||
|
|
<SPAN CLASS="cmr"
|
||
|
|
>⊳</SPAN
|
||
|
|
> (SETF (GETHASH 1 HASH-TABLE) ONE)
|
||
|
|
<SPAN CLASS="cmr"
|
||
|
|
>⊳</SPAN
|
||
|
|
> (SETF (GETHASH 2 HASH-TABLE) TWO)
|
||
|
|
<SPAN CLASS="cmr"
|
||
|
|
>⊳</SPAN
|
||
|
|
> HASH-TABLE)
|
||
|
|
<SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> #<HASH-TABLE EQL 0/120 32005763></PRE
|
||
|
|
></DD
|
||
|
|
><DT
|
||
|
|
><B
|
||
|
|
>See Also</B
|
||
|
|
></DT
|
||
|
|
><DD
|
||
|
|
><P CLASS="j"
|
||
|
|
><A HREF="f_write.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>write</B
|
||
|
|
></A
|
||
|
|
>, <A HREF="f_print-unreadable-object.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>print-unreadable-object</B
|
||
|
|
></A
|
||
|
|
></P
|
||
|
|
></DD
|
||
|
|
><DT
|
||
|
|
><B
|
||
|
|
>Notes</B
|
||
|
|
></DT
|
||
|
|
><DD
|
||
|
|
><P CLASS="j"
|
||
|
|
>The rules for “<A HREF="26_1_Glossary.html#similarity"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>similarity</EM
|
||
|
|
></A
|
||
|
|
>” imply that <CODE CLASS="f"
|
||
|
|
>#A</CODE
|
||
|
|
> or <CODE CLASS="f"
|
||
|
|
>#(</CODE
|
||
|
|
> syntax cannot be used for <A HREF="26_1_Glossary.html#array"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>arrays</EM
|
||
|
|
></A
|
||
|
|
> of <A HREF="26_1_Glossary.html#element_type"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>element type</EM
|
||
|
|
></A
|
||
|
|
> other than <A HREF="t_t.html" CLASS="typeref"
|
||
|
|
><B
|
||
|
|
>t</B
|
||
|
|
></A
|
||
|
|
>. An implementation will have to use another syntax or signal an error of <A HREF="26_1_Glossary.html#type"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>type</EM
|
||
|
|
></A
|
||
|
|
> <A HREF="t_print-not-readable.html" CLASS="typeref"
|
||
|
|
><B
|
||
|
|
>print-not-readable</B
|
||
|
|
></A
|
||
|
|
>.</P
|
||
|
|
></DD
|
||
|
|
></DL
|
||
|
|
></DIV
|
||
|
|
></DIV
|
||
|
|
><DIV CLASS="footer"
|
||
|
|
><DIV CLASS="btmnav"
|
||
|
|
><A HREF="v_print-pretty.html" CLASS="prev"
|
||
|
|
>←</A
|
||
|
|
><A HREF="v_print-right-margin.html" CLASS="next"
|
||
|
|
>→</A
|
||
|
|
></DIV
|
||
|
|
><DIV CLASS="trail"
|
||
|
|
>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
|
||
|
|
></DIV
|
||
|
|
></DIV
|
||
|
|
><SCRIPT
|
||
|
|
>domReady();</SCRIPT
|
||
|
|
></BODY
|
||
|
|
></HTML
|
||
|
|
>
|