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86 lines
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<TITLE>27.2. Pretty Printing Control Variables</TITLE>
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<meta name="description" value=" Pretty Printing Control Variables">
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html4752 HREF="node256.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4750 HREF="node253.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4744 HREF="node254.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4754 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4755 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4753 HREF="node256.html"> Dynamic Control of </A>
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<B>Up:</B> <A NAME=tex2html4751 HREF="node253.html"> Pretty Printing</A>
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<B> Previous:</B> <A NAME=tex2html4745 HREF="node254.html"> Introduction</A>
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<HR> <P>
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<H1><A NAME=SECTION003120000000000000000>27.2. Pretty Printing Control Variables</A></H1>
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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<A NAME=PPRINTVARIABLESSECTION>The</A>
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function <tt>write</tt> accepts keyword arguments named
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<tt>:pprint-dispatch</tt>, <tt>:miser-width</tt>, <tt>:right-margin</tt>, and <tt>:lines</tt>,
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corresponding to these variables.
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<P>
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<BR><b>[Variable]</b><BR>
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<tt>*print-pprint-dispatch*</tt><P>When <tt>*print-pretty*</tt> is not <tt>nil</tt>, printing is controlled by the `pprint
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dispatch table' stored in the variable <tt>*print-pprint-dispatch*</tt>. The
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initial value of <tt>*print-pprint-dispatch*</tt> is implementation-dependent and
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causes traditional pretty printing of Lisp code. The last section of this
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chapter explains how the contents of this table can be changed.
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<P>
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<BR><b>[Variable]</b><BR>
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<tt>*print-right-margin*</tt><P>A primary goal of pretty printing is to keep the output between a pair of
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margins. The left margin is set at the column where the output begins. If
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this cannot be determined, the left margin is set to zero.
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<P>
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When <tt>*print-right-margin*</tt> is not <tt>nil</tt>, it specifies the right
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margin to use when making layout decisions. When <tt>*print-right-margin*</tt>
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is <tt>nil</tt> (the initial value), the right margin is set at the maximum
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line length that can be displayed by the output stream without wraparound
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or truncation. If this cannot be determined, the right margin is set to an
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implementation-dependent value.
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<P>
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To allow for the possibility of variable-width fonts,
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<tt>*print-right-margin*</tt> is in units of ems-the width of an
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``m'' in the font being used to display characters on the relevant output
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stream at the moment when the variables are consulted.
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<P>
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<BR><b>[Variable]</b><BR>
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<tt>*print-miser-width*</tt><P>If <tt>*print-miser-width*</tt> is not <tt>nil</tt>, the pretty printer switches to a compact
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style of output (called miser style) whenever the width available for
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printing a substructure is less than or equal to <tt>*print-miser-width*</tt> ems.
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The initial value of <tt>*print-miser-width*</tt> is implementation-dependent.
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<P>
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<BR><b>[Variable]</b><BR>
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<tt>*print-lines*</tt><P>When given a value other than its initial value of <tt>nil</tt>,
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<tt>*print-lines*</tt> limits the number of output lines produced when
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something is pretty printed. If an attempt is made to go beyond
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<tt>*print-lines*</tt> lines, ``<tt> ..</tt>'' (a space and two periods)
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is printed at the end of the last
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line followed by all of the suffixes (closing delimiters) that are pending
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to be printed.
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<P><pre>
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(let ((*print-right-margin* 25) (*print-lines* 3))
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(pprint '(progn (setq a 1 b 2 c 3 d 4))))
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<BR>(PROGN (SETQ A 1
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B 2
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C 3 ..))
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</pre><P>
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<P>
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(The symbol ``<tt>..</tt>'' is printed out to ensure that a reader error will
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occur if the output is later read. A symbol different from ``<tt>...</tt>'' is
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used to indicate that a different kind of abbreviation has occurred.)
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR> <HR><A NAME=tex2html4752 HREF="node256.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4750 HREF="node253.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4744 HREF="node254.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4754 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4755 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4753 HREF="node256.html"> Dynamic Control of </A>
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<B>Up:</B> <A NAME=tex2html4751 HREF="node253.html"> Pretty Printing</A>
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<B> Previous:</B> <A NAME=tex2html4745 HREF="node254.html"> Introduction</A>
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<HR> <P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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