121 lines
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121 lines
6.8 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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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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<HEAD>
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<TITLE>13.5. Character Control-Bit Functions</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Character Control-Bit Functions">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html3272 HREF="node141.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3270 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3266 HREF="node139.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3274 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3275 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3273 HREF="node141.html"> Sequences</A>
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<B>Up:</B> <A NAME=tex2html3271 HREF="node135.html"> Characters</A>
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<B> Previous:</B> <A NAME=tex2html3267 HREF="node139.html"> Character Conversions</A>
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<HR> <P>
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<H1><A NAME=SECTION001750000000000000000>13.5. Character Control-Bit Functions</A></H1>
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<P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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Common Lisp provides explicit names for four bits of the bits attribute:
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<i>Control</i>, <i>Meta</i>, <i>Hyper</i>, and <i>Super</i>. The following
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definitions are provided for manipulating these.
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Each Common Lisp implementation provides these functions for compatibility,
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even if it does not support any or all of the bits named below.
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>char-control-bit</tt> <tt><BR></tt><tt>char-meta-bit</tt> <tt><BR></tt><tt>char-super-bit</tt> <tt><BR></tt><tt>char-hyper-bit</tt><P>The values of these named constants are the ``weights'' (as integers) for
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the four named control bits. The weight of the control bit is <tt>1</tt>;
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of the meta bit, <tt>2</tt>; of the super bit, <tt>4</tt>; and of the hyper bit, <tt>8</tt>.
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<P>
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If a given implementation of Common Lisp does not support a particular bit,
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then the corresponding constant is zero instead.
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<br><img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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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X3J13 voted in March 1989 (CHARACTER-PROPOSAL) <A NAME=15068> </A>
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to eliminate all four of the constants
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<tt>char-control-bit</tt>, <tt>char-meta-bit</tt>, <tt>char-super-bit</tt>,
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and <tt>char-hyper-bit</tt>.
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<P>
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<P>When Common Lisp was first designed, keyboards with ``extra bits'' were
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relatively rare. The bits attribute was originally designed to support input
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from keyboards in use at Stanford and M.I.T. circa 1981.
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<P>
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Since that time such extended keyboards have come into wider use.
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Notable here are the keyboards associated with certain
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personal computers and workstations. For example, in some specific applications
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the <i>command</i> and <i>option</i> keys of Apple Macintosh keyboards have
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had the connotations of <i>control</i> and <i>meta</i>. Macintosh II
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extended keyboards also have keys marked <i>control</i> whose use
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is analogous to that of <i>hyper</i> on the old M.I.T. keyboards.
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IBM PC personal computer keyboards have <i>alt</i> keys that function
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much like <i>meta</i> keys; similarly, keyboards on Sun workstations
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have keys very much like <i>meta</i> keys but labelled <i>left</i> and <i>right</i>.
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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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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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<BR><b>[Function]</b><BR>
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<tt>char-bit <i>char</i> <i>name</i></tt><P><tt>char-bit</tt> takes a character object <i>char</i> and the name of a bit,
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and returns non-<tt>nil</tt> if the bit of that name is set in <i>char</i>,
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or <tt>nil</tt> if the bit is not set in <i>char</i>.
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For example:
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<P><pre>
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(char-bit #\Control-X <tt>:control</tt>) => <i>true</i>
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</pre><P>
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Valid values for <i>name</i>
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are implementation-dependent, but typically are <tt>:control</tt>,
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<tt>:meta</tt>, <tt>:hyper</tt>, and <tt>:super</tt>.
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It is an error to give <tt>char-bit</tt> the name of a bit not supported
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by the implementation.
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<P>
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If the argument <i>char</i> is specified by a form that is a <i>place</i> form
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acceptable to <tt>setf</tt>,
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then <tt>setf</tt> may be used with <tt>char-bit</tt>
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to modify a bit of the character stored in that
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<i>place</i>.
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The effect is to perform a <tt>set-char-bit</tt> operation
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and then store the result back into the <i>place</i>.
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<br><img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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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X3J13 voted in March 1989 (CHARACTER-PROPOSAL) <A NAME=15117> </A>
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to eliminate <tt>char-bit</tt>.
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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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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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<BR><b>[Function]</b><BR>
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<tt>set-char-bit <i>char</i> <i>name</i> <i>newvalue</i></tt><P><tt>char-bit</tt> takes a character object <i>char</i>, the name of a bit,
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and a flag. A character is returned that is just like <i>char</i>
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except that the named bit is set or reset according to whether
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<i>newvalue</i> is non-<tt>nil</tt> or <tt>nil</tt>.
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Valid values for <i>name</i>
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are implementation-dependent, but typically are <tt>:control</tt>,
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<tt>:meta</tt>, <tt>:hyper</tt>, and <tt>:super</tt>.
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For example:
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<pre>
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(set-char-bit #\X <tt>:control</tt> t) => #\Control-X
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(set-char-bit #\Control-X <tt>:control</tt> t) => #\Control-X
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(set-char-bit #\Control-X <tt>:control</tt> <tt>nil</tt>) => #\X
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</pre>
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<br><img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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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X3J13 voted in March 1989 (CHARACTER-PROPOSAL) <A NAME=15148> </A>
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to eliminate <tt>set-char-bit</tt>.
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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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<P>
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<BR> <HR><A NAME=tex2html3272 HREF="node141.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3270 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3266 HREF="node139.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3274 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3275 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3273 HREF="node141.html"> Sequences</A>
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<B>Up:</B> <A NAME=tex2html3271 HREF="node135.html"> Characters</A>
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<B> Previous:</B> <A NAME=tex2html3267 HREF="node139.html"> Character Conversions</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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</ADDRESS>
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</BODY>
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