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116 lines
5.4 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>4.4. Type Specifiers That Combine</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Type Specifiers That Combine">
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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=tex2html2103 HREF="node49.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2101 HREF="node44.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2095 HREF="node47.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2105 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2106 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2104 HREF="node49.html"> Type Specifiers That </A>
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<B>Up:</B> <A NAME=tex2html2102 HREF="node44.html"> Type Specifiers</A>
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<B> Previous:</B> <A NAME=tex2html2096 HREF="node47.html"> Predicating Type Specifiers</A>
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<HR> <P>
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<H1><A NAME=SECTION00840000000000000000>4.4. Type Specifiers That Combine</A></H1>
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<P>
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The following type specifier lists define a type in terms of
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other types or objects.
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<P>
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<DL COMPACT><DT><tt>(member <i>object1</i> <i>object2</i> ...)</tt>
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<DD>
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This denotes the set
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containing precisely those objects named. An object is of
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this type if and only if it is <tt>eql</tt> to one of the specified objects.
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</DL>
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<P>
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<hr>
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<b>Compatibility note:</b> This is roughly equivalent to
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the Interlisp DECL package's <tt>memq</tt>.
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<hr><P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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<P>
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<DL COMPACT><DT><tt>(eql <i>object</i>)</tt>
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<DD>
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X3J13 voted in June 1988 (CLOS) <A NAME=2168> </A> to add the <tt>eql</tt> type specifier.
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It may be used as a parameter specializer for CLOS methods
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(see section <A HREF="node279.html#IntroductiontoMethodsSECTION">28.1.6.2</A>
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and <tt>find-method</tt>).
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It denotes the set of the one object named; an object is of
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this type if and only if it is <tt>eql</tt> to <i>object</i>. While
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<tt>(eql <i>object</i>)</tt> denotes the same type as <tt>(member <i>object</i>)</tt>,
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only <tt>(eql <i>object</i>)</tt> may be used as a CLOS parameter specializer.
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<P>
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</DL>
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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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<DL COMPACT><DT><tt>(not <i>type</i>)</tt>
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<DD>
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This denotes the set of all those objects that
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are <i>not</i> of the specified type.
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<P>
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<DT><tt>(and <i>type1</i> <i>type2</i> ...)</tt>
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<DD>
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This denotes the intersection of
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the specified types.
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</DL><P>
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<hr>
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<b>Compatibility note:</b> This is roughly equivalent to
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the Interlisp DECL package's <tt>allof</tt>.
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<hr><P>
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<DL COMPACT><dd>
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When <tt>typep</tt> processes an <tt>and</tt> type specifier, it always
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tests each of the component types in order from left to right
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and stops processing as soon as one component of the intersection has
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been found to which the object in question does not belong.
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In this respect an <tt>and</tt> type specifier is similar to an
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executable <tt>and</tt> form. The purpose of this similarity is to allow
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a <tt>satisfies</tt> type specifier to depend on filtering by previous
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type specifiers. For example, suppose there were a function <tt>primep</tt>
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that takes an integer and says whether it is prime. Suppose also that
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it is an error to give any object other than an integer to <tt>primep</tt>.
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Then the type specifier
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<P><pre>
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(and integer (satisfies primep))
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</pre><P>
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is guaranteed never to result in an error because the function <tt>primep</tt>
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will not be invoked unless the object in question has already been
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determined to be an integer.
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<P>
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<DT><tt>(or <i>type1</i> <i>type2</i> ...)</tt>
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<DD>
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This denotes the union of the
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specified types. For example, the type <tt>list</tt> by definition is the same as
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<tt>(or null cons)</tt>. Also, the value returned by the function
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<tt>position</tt> is always of type <tt>(or null (integer 0 *))</tt>
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(either <tt>nil</tt> or a non-negative integer).
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</dl>
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<P>
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<hr>
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<b>Compatibility note:</b> This is roughly equivalent to
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the Interlisp DECL package's <tt>oneof</tt>.
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<hr>
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<P>
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<dl compact><dd>
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As for <tt>and</tt>,
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when <tt>typep</tt> processes an <tt>or</tt> type specifier, it always
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tests each of the component types in order from left to right
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and stops processing as soon as one component of the union has
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been found to which the object in question belongs.
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<P>
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</DL>
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<P>
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<BR> <HR><A NAME=tex2html2103 HREF="node49.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2101 HREF="node44.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2095 HREF="node47.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2105 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2106 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2104 HREF="node49.html"> Type Specifiers That </A>
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<B>Up:</B> <A NAME=tex2html2102 HREF="node44.html"> Type Specifiers</A>
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<B> Previous:</B> <A NAME=tex2html2096 HREF="node47.html"> Predicating Type Specifiers</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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