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167 lines
9.8 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>23.1.5.3. Using Logical Pathnames</TITLE>
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<BODY>
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<meta name="description" value=" Using Logical Pathnames">
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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=tex2html4196 HREF="node212.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4194 HREF="node208.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4188 HREF="node210.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4198 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4199 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4197 HREF="node212.html"> Examples of the </A>
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<B>Up:</B> <A NAME=tex2html4195 HREF="node208.html"> Logical Pathnames</A>
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<B> Previous:</B> <A NAME=tex2html4189 HREF="node210.html"> Parsing of Logical </A>
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<HR> <P>
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<H3><A NAME=SECTION002715300000000000000>23.1.5.3. Using Logical Pathnames</A></H3>
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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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Some real file systems do not have versions. Logical pathname
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translation to such a file system ignores the version. This implies that
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a portable program cannot rely on being able to store in a file system
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more than one version of a
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file named by a logical pathname.
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<P>
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The type of a logical pathname for a Common Lisp source file is <tt>LISP</tt>.
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This should be translated into whatever implementation-defined
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type is appropriate in a physical pathname.
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<P>
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The logical pathname host name <tt>SYS</tt> is reserved for the implementation.
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The existence and meaning of logical pathnames for logical host <tt>SYS</tt> is
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implementation-defined.
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<P>
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File manipulation functions must operate with logical pathnames
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according to the following requirements:
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<UL><LI> The following accept logical pathnames
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and translate them into physical pathnames as if by calling the
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function <tt>translate-logical-pathname</tt>:
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<pre>
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compile-file ed probe-file
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compile-file-pathname file-author rename-file
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delete-file file-write-date truename
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directory load with-open-file
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dribble open
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</pre>
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<P>
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<LI> Applying the function <tt>pathname</tt> to a stream created by the function <tt>open</tt>
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or the macro <tt>with-open-file</tt> using a logical pathname produces a logical pathname.
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<P>
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<LI> The functions <tt>truename</tt>, <tt>probe-file</tt>, and <tt>directory</tt>
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never return logical pathnames.
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<P>
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<LI> Calling <tt>rename-file</tt> with a logical pathname as the second argument returns a
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logical pathname as the first value.
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<P>
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<LI> <tt>make-pathname</tt> returns a logical pathname if and only if the host is
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logical. If the <tt>:host</tt> argument to <tt>make-pathname</tt> is supplied, the host is
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logical if it came from the <tt>pathname-host</tt> of a logical pathname. Whether a
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<tt>:host</tt> argument is logical if it is a string equal to a logical pathname
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host name is implementation-defined.
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</UL>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>logical-pathname <i>pathname</i></tt><P> Converts the argument to a logical pathname and returns it. The
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argument can be a logical pathname, a logical pathname namestring
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containing a host component, or a stream for which the <tt>pathname</tt>
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function returns a logical pathname. For any other argument,
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<tt>logical-pathname</tt> signals an error of type <tt>type-error</tt>.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>translate-logical-pathname <i>pathname</i> &key</tt><P> Translates a logical pathname to the corresponding physical pathname.
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The <i>pathname</i> argument is first coerced to a pathname. If it is not a
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pathname, string, or file stream, an error of type <tt>type-error</tt> is
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signaled.
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<P>
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If the coerced argument is a physical pathname, it is returned.
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<P>
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If the coerced argument is a logical pathname, the first matching
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translation (according to <tt>pathname-match-p</tt>) of the logical pathname
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host is applied, as if by calling <tt>translate-pathname</tt>. If the result is
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a logical pathname, this process is repeated. When the result is
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finally a physical pathname, it is returned.
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<P>
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If no translation matches a logical pathname,
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an error of type <tt>file-error</tt> is signaled.
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<P>
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<tt>translate-logical-pathname</tt> may perform additional translations,
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typically to provide translation of file types to local naming
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conventions, to accommodate physical file systems with names of limited length,
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or to deal with special character requirements such as
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translating hyphens to underscores or uppercase letters to lowercase.
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Any such additional translations are implementation-defined. Some
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implementations do no additional translations.
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<P>
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There are no specified keyword arguments for
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<tt>translate-logical-pathname</tt> but implementations are permitted to extend
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it by adding keyword arguments. There is one specified return value
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from <tt>translate-logical-pathname</tt>; implementations are permitted to
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extend it by returning additional values.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>logical-pathname-translations <i>host</i></tt><P> If the specified <i>host</i> is not the host component of a logical pathname and is not a
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string that has been defined as a logical pathname host name by <tt>setf</tt> of
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<tt>logical-pathname-translations</tt>, this function signals an error of type <tt>type-error</tt>;
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otherwise, it returns the list of translations for the specified <i>host</i>. Each translation is
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a list of at least two elements, from-wildname and to-wildname. Any
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additional elements are implementation-defined. A from-wildname is a
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logical pathname whose host is the specified <i>host</i>. A to-wildname is any pathname.
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Translations are searched in the order listed, so more specific
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from-wildnames must precede more general ones.
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<P>
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<tt>(setf (logical-pathname-translations <i>host</i>) <i>translations</i>)</tt>
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sets the list of translations for the logical
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pathname <i>host</i> to <i>translations</i>. If <i>host</i> is a string that has
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not previously been used as logical pathname host, a new logical
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pathname host is defined; otherwise an existing host's translations are
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replaced. Logical pathname host names are compared with <tt>string-equal</tt>.
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<P>
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When setting the translations list, each from-wildname can be a logical
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pathname whose host is <i>host</i> or a logical pathname namestring <i>s</i>
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parseable by <tt>(parse-namestring <i>s</i> <i>host-object</i>)</tt>, where <i>host-object</i>
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is an appropriate object for representing the specified <i>host</i> to
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<tt>parse-namestring</tt>. (This circuitous specification dodges the fact
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that <tt>parse-namestring</tt> does not necessarily accept as its second argument
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any old string that names a logical host.)
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Each to-wildname can be anything coercible to a pathname by application of
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the function <tt>pathname</tt>.
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If to-wildname coerces to a logical pathname,
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<tt>translate-logical-pathname</tt> will retranslate the result, repeatedly if
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necessary.
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<P>
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Implementations may define additional functions that operate on
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logical pathname hosts (for example, to specify additional translation
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rules or options).
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<P>
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<BR><b>[Function]</b><BR>
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<tt>load-logical-pathname-translations <i>host</i></tt><P> If a logical pathname host named <i>host</i> (a string) is already defined,
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this function returns <tt>nil</tt>. Otherwise, it searches for a logical pathname host definition
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in an implementation-defined manner. If none is found, it signals an
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error. If a definition is found, it installs the definition and returns <tt>t</tt>.
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<P>
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The search used by <tt>load-logical-pathname-translations</tt> should be
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documented, as logical pathname definitions will be created by users as well as
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by Lisp implementors. A typical search technique is to
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look in an implementation-defined directory for a file whose name is derived from
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the host name in an implementation-defined fashion.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>compile-file-pathname <i>pathname</i> &key :output-file</tt><P> Returns the pathname that <tt>compile-file</tt> would write into, if given the
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same arguments. If the pathname argument is a logical pathname and the
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<tt>:output-file</tt> argument is unspecified, the result is a logical pathname.
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If an implementation supports additional keyword arguments to
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<tt>compile-file</tt>, <tt>compile-file-pathname</tt> must accept the same arguments.
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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=tex2html4196 HREF="node212.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4194 HREF="node208.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4188 HREF="node210.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4198 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4199 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4197 HREF="node212.html"> Examples of the </A>
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<B>Up:</B> <A NAME=tex2html4195 HREF="node208.html"> Logical Pathnames</A>
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<B> Previous:</B> <A NAME=tex2html4189 HREF="node210.html"> Parsing of Logical </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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