60 lines
3.9 KiB
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60 lines
3.9 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>29.3.14. Condition Types</TITLE>
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<BODY>
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<meta name="description" value=" Condition Types">
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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=tex2html5803 HREF="node330.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5801 HREF="node315.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5795 HREF="node328.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5805 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5806 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5804 HREF="node330.html"> Signaling Conditions</A>
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<B>Up:</B> <A NAME=tex2html5802 HREF="node315.html"> Survey of Concepts</A>
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<B> Previous:</B> <A NAME=tex2html5796 HREF="node328.html"> Non-Serious Conditions</A>
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<HR> <P>
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<H2><A NAME=SECTION0033314000000000000000>29.3.14. Condition Types</A></H2>
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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 types of conditions are predefined by the system. All types of conditions
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are subtypes of <tt>condition</tt>. That is, <tt>(typep <i>x</i> 'condition)</tt> is true if
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and only if the value of <i>x</i> is a condition.
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<P>
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Implementations supporting multiple (or non-hierarchical) type inheritance
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are expressly permitted to exploit multiple inheritance in the tree of
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condition types as implementation-dependent extensions, as long as such
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extensions are compatible with the specifications in this chapter.
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[X3J13 voted in March 1989 (ZLOS-CONDITIONS) <A NAME=36600> </A>
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to integrate the Condition System and the Object System,
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so multiple inheritance is always available for condition types.-GLS]
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<P>
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In order to avoid problems in portable code that runs both in systems with
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multiple type inheritance and in systems without it, programmers are explicitly
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warned that while all correct Common Lisp implementations will ensure that
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<tt>(typep <i>c</i> 'condition)</tt>
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is true for all conditions <i>c</i> (and all subtype relationships indicated in this
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chapter will also be true), it should <i>not</i> be assumed that two condition
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types specified to be subtypes of the same third type are disjoint.
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(In some cases,
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disjoint subtypes are identified explicitly, but such disjointness is not to be assumed by
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default.) For example, it follows from the subtype descriptions contained in
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this chapter that in all implementations
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<tt>(typep <i>c</i> 'control-error)</tt> implies <tt>(typep <i>c</i> 'error)</tt>,
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but note that
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<tt>(typep <i>c</i> 'control-error)</tt> does <i>not</i>
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imply <tt>(not (typep <i>c</i> 'cell-error))</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> <HR><A NAME=tex2html5803 HREF="node330.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5801 HREF="node315.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5795 HREF="node328.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5805 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5806 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5804 HREF="node330.html"> Signaling Conditions</A>
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<B>Up:</B> <A NAME=tex2html5802 HREF="node315.html"> Survey of Concepts</A>
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<B> Previous:</B> <A NAME=tex2html5796 HREF="node328.html"> Non-Serious Conditions</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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