90 lines
4.8 KiB
HTML
90 lines
4.8 KiB
HTML
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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>2.5.2. Strings</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Strings">
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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=tex2html1893 HREF="node32.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1891 HREF="node29.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1885 HREF="node30.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html1895 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html1896 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html1894 HREF="node32.html"> Bit-Vectors</A>
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<B>Up:</B> <A NAME=tex2html1892 HREF="node29.html"> Arrays</A>
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<B> Previous:</B> <A NAME=tex2html1886 HREF="node30.html"> Vectors</A>
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<HR> <P>
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<H2><A NAME=SECTION00652000000000000000>2.5.2. Strings</A></H2>
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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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<A NAME=STRINGTYPESECTION>A</A>
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string is simply a vector of characters.
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More precisely, a string is a specialized vector whose elements
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are of type <tt>string-char</tt>.
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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=1261> </A>
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to eliminate the type <tt>string-char</tt> and to redefine the type
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<tt>string</tt> to be the union of one or more specialized vector
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types, the types of whose elements are subtypes of the type <tt>character</tt>.
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Subtypes of <tt>string</tt> include <tt>simple-string</tt>, <tt>base-string</tt>,
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and <tt>simple-base-string</tt>.
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<P>
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<P><pre>
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base-string == (vector base-character)
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simple-base-string == (simple-array base-character (*))
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</pre><P>
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An implementation may support
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other string subtypes as well. All Common Lisp functions that operate
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on strings treat all strings uniformly; note, however,
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that it is an error to attempt to insert
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an extended character into a base string.
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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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The type <tt>string</tt> is therefore a subtype of the type <tt>vector</tt>.
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<P>
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A string can be written as the sequence of characters contained in the
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string, preceded and followed by a <tt>"</tt> (double quote) character.
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Any <tt>"</tt> or <tt>\</tt> character in the sequence must additionally
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have a <tt>\</tt> character before it.
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<P>
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For example:
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<P>
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<P><pre>
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"Foo" ;A string with three characters in it
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"" ;An empty string
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"\"APL\\360?\" he cried." ;A string with twenty characters
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"|x| = |-x|" ;A ten-character string
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</pre><P>
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Notice that any vertical bar <tt>|</tt> in a string need not be
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preceded by a <tt>\</tt>. Similarly, any double quote in the name
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of a symbol written using vertical-bar notation need not be
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preceded by a <tt>\</tt>. The double-quote and vertical-bar notations
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are similar but distinct: double quotes indicate a character string
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containing the sequence of characters,
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whereas vertical bars indicate a symbol whose name is the contained
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sequence of characters.
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<P>
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The characters contained by the double quotes, taken from left to right,
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occupy locations within the string with increasing indices.
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The leftmost character is string element number 0, the next one
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is element number 1, the next one is element number 2, and so on.
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<P>
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Note that the function <tt>prin1</tt> will print any character vector
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(not just a simple one)
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using this syntax, but the function <tt>read</tt> will always construct
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a simple string when it reads this syntax.
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<P>
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<BR> <HR><A NAME=tex2html1893 HREF="node32.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1891 HREF="node29.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1885 HREF="node30.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html1895 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html1896 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html1894 HREF="node32.html"> Bit-Vectors</A>
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<B>Up:</B> <A NAME=tex2html1892 HREF="node29.html"> Arrays</A>
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<B> Previous:</B> <A NAME=tex2html1886 HREF="node30.html"> Vectors</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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