179 lines
9.2 KiB
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179 lines
9.2 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>13.4. Character Conversions</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Character Conversions">
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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=tex2html3262 HREF="node140.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3260 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3254 HREF="node138.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3264 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3265 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3263 HREF="node140.html"> Character Control-Bit Functions</A>
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<B>Up:</B> <A NAME=tex2html3261 HREF="node135.html"> Characters</A>
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<B> Previous:</B> <A NAME=tex2html3255 HREF="node138.html"> Character Construction and </A>
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<HR> <P>
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<H1><A NAME=SECTION001740000000000000000>13.4. Character Conversions</A></H1>
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<P>
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These functions perform various transformations on characters,
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including case conversions.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>character <i>object</i></tt><P>The function <tt>character</tt> coerces its argument to be a character
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if possible; see <tt>coerce</tt>.
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<P><pre>
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(character x) == (coerce x 'character)
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</pre><P>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>char-upcase <i>char</i> <BR></tt><tt>char-downcase <i>char</i></tt><P>The argument <i>char</i> must be a character object.
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<tt>char-upcase</tt> attempts to convert its argument to an uppercase
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equivalent; <tt>char-downcase</tt> attempts to convert its argument
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to a lowercase equivalent.
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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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<tt>char-upcase</tt> returns a character object with the same font
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and bits attributes as <i>char</i>, but with possibly a different code
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attribute. If the code is different from <i>char</i>'s, then the predicate
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<tt>lower-case-p</tt> is true of <i>char</i>, and <tt>upper-case-p</tt>
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is true of the result character. Moreover, if <tt>(char= (char-upcase x) x)</tt>
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is <i>not</i> true, then it is true that
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<P><pre>
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(char= (char-downcase (char-upcase x)) x)
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</pre><P>
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Similarly,
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<tt>char-downcase</tt> returns a character object with the same font
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and bits attributes as <i>char</i>, but with possibly a different code
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attribute. If the code is different from <i>char</i>'s, then the predicate
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<tt>upper-case-p</tt> is true of <i>char</i>, and <tt>lower-case-p</tt>
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is true of the result character. Moreover, if <tt>(char= (char-downcase x) x)</tt>
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is <i>not</i> true, then it is true that
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<P><pre>
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(char= (char-upcase (char-downcase x)) 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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Note that the action of <tt>char-upcase</tt> and <tt>char-downcase</tt> may
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depend on the bits and font attributes of the character. In particular,
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they have no effect on a character with a non-zero bits attribute,
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because such characters are by definition not alphabetic.
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See <tt>alpha-char-p</tt>.
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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=14961> </A>
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to replace the notion of bits and font attributes with
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that of implementation-defined attributes. The effect of
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<tt>char-upcase</tt> and <tt>char-downcase</tt> is to preserve
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implementation-defined attributes.
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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><b>[Function]</b><BR>
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<tt>digit-char <i>weight</i> &optional (<i>radix</i> 10) (<i>font</i> 0)</tt><P>All arguments must be integers. <tt>digit-char</tt>
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determines whether or not it is possible to construct
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a character object
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whose font attribute is <i>font</i>, and whose <i>code</i> is such that the
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result character has the weight <i>weight</i> when considered as
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a digit of the radix <i>radix</i> (see the predicate <tt>digit-char-p</tt>).
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It returns such a character if that is possible, and otherwise returns <tt>nil</tt>.
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<P>
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<tt>digit-char</tt> cannot return <tt>nil</tt> if <i>font</i> is zero,
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<i>radix</i> is between 2 and 36 inclusive, and <i>weight</i> is non-negative
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and less than <i>radix</i>.
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<P>
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If more than one character object can encode
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such a weight in the given radix, one will be chosen consistently
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by any given implementation; moreover, among the standard characters,
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uppercase letters are preferred to lowercase letters.
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For example:
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<P><pre>
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(digit-char 7) => #\7
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(digit-char 12) => <tt>nil</tt>
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(digit-char 12 16) => #\C ;not #\c
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(digit-char 6 2) => <tt>nil</tt>
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(digit-char 1 2) => #\1
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</pre><P>
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Note that no argument is provided for specifying the <i>bits</i> component
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of the returned character, because a digit cannot have a non-zero
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<i>bits</i> component. The reasoning is that every digit is graphic
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(see <tt>digit-char-p</tt>) and no graphic character has a non-zero
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<i>bits</i> component (see <tt>graphic-char-p</tt>).
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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=14995> </A>
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to eliminate the <i>font</i> argument from the specification of <tt>digit-char</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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<BR><b>[Function]</b><BR>
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<tt>char-int <i>char</i></tt><P>The argument <i>char</i> must be a character object.
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<tt>char-int</tt> returns a non-negative integer encoding the character object.
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<P>
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If the font and bits attributes of <i>char</i> are zero, then
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<tt>char-int</tt> returns the same integer <tt>char-code</tt> would.
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Also,
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<P><pre>
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(char= c1 c2) == (= (char-int c1) (char-int c2))
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</pre><P>
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for characters <tt>c1</tt> and <tt>c2</tt>.
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<P>
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This function is provided primarily for the purpose of hashing characters.
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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>int-char <i>integer</i></tt><P>The argument must be a non-negative integer.
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<tt>int-char</tt> returns a character object <tt>c</tt> such that
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<tt>(char-int c)</tt> is equal to <i>integer</i>, if possible; otherwise
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<tt>int-char</tt> returns false.
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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=15021> </A>
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to eliminate <tt>int-char</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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<BR><b>[Function]</b><BR>
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<tt>char-name <i>char</i></tt><P>The argument <i>char</i> must be a character object.
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If the character has a name, then that name (a string) is returned;
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otherwise <tt>nil</tt> is returned. All characters that have
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zero font and bits attributes and that are non-graphic
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(do not satisfy the predicate <tt>graphic-char-p</tt>) have names.
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Graphic characters may or may not have names.
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<P>
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The standard newline and space characters have the respective
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names <tt>Newline</tt> and <tt>Space</tt>.
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The semi-standard characters have the names
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<tt>Tab</tt>, <tt>Page</tt>, <tt>Rubout</tt>, <tt>Linefeed</tt>, <tt>Return</tt>, and <tt>Backspace</tt>.
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<P>
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Characters that have names can be notated as <tt>#\</tt> followed
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by the name. (See section <A HREF="node191.html#SHARPSIGNMACROCHARACTERSECTION">22.1.4</A>.)
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Although the name may be written in any case,
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it is stylish to capitalize it thus: <tt>#\Space</tt>.
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<P>
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<tt>char-name</tt> will only locate ``simple'' character names;
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it will not construct names such as <tt>Control-Space</tt> on the
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basis of the character's bits attribute.
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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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The easiest way to get a name that includes the bits attribute of
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a character <tt>c</tt> is <tt>(format nil "~:C" c)</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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<BR><b>[Function]</b><BR>
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<tt>name-char <i>name</i></tt><P>The argument <tt>name</tt> must be an object coerceable to a string
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as if by the function <tt>string</tt>.
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If the name is the same as the name of a character object
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(as determined by <tt>string-equal</tt>), that object
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is returned; otherwise <tt>nil</tt> is returned.
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<P>
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<BR> <HR><A NAME=tex2html3262 HREF="node140.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html3260 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html3254 HREF="node138.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html3264 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html3265 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3263 HREF="node140.html"> Character Control-Bit Functions</A>
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<B>Up:</B> <A NAME=tex2html3261 HREF="node135.html"> Characters</A>
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<B> Previous:</B> <A NAME=tex2html3255 HREF="node138.html"> Character Construction and </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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