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76 lines
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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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<TITLE> 1.2.4. Errors</TITLE>
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<meta name="description" value=" Errors">
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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=tex2html1620 HREF="node12.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1618 HREF="node7.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1612 HREF="node10.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html1622 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html1623 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html1621 HREF="node12.html"> Descriptions of Functions </A>
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<B>Up:</B> <A NAME=tex2html1619 HREF="node7.html"> Notational Conventions</A>
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<B> Previous:</B> <A NAME=tex2html1613 HREF="node10.html"> EvaluationExpansion, and </A>
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<HR> <P>
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<H2><A NAME=SECTION00524000000000000000> 1.2.4. Errors</A></H2>
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<A NAME=INTROERRORS>When</A>
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this book specifies that it ``is an error'' for some situation
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to occur, this means that:
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<UL><LI> No valid Common Lisp program should cause this situation to occur.
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<P>
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<LI> If this situation occurs, the effects and results are completely
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undefined as far as adherence to the Common Lisp specification is concerned.
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<P>
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<LI> No Common Lisp implementation is required to detect such an error.
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Of course, implementors are encouraged to provide for detection
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of such errors wherever reasonable.
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</UL>
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This is not to say that some particular implementation might not define
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the effects and results for such a situation; the point is that no program
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conforming to the Common Lisp specification may correctly depend on such
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effects or results.
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<P>
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On the other hand, if it is specified in this book that in some situation
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``an error is <i>signaled</i>,'' this means that:
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<UL><LI> If this situation occurs, an error will be signaled
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(see <tt>error</tt> and <tt>cerror</tt>).
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<P>
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<LI> Valid Common Lisp programs may rely on the fact that an error will be signaled.
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<P>
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<LI> Every Common Lisp implementation is required to detect such an error.
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</UL>
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<P>
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In places where it is stated that so-and-so ``must'' or ``must not''
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or ``may not'' be the case, then it ``is an error'' if the stated requirement
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is not met. For example, if an argument ``must be a symbol,'' then it
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``is an error'' if the argument is not a symbol. In all cases where
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an error is to be <i>signaled</i>, the word ``signaled'' is always used
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explicitly in this book.
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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 has adopted a more elaborate terminology for errors,
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and has made some effort to specify the type of error to be signaled
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in situations where signaling is appropriate. This effort
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was not complete as of September 1989, and I have made little
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attempt to incorporate the new error terminology or
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error type specifications in this book. However, the new terminology
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is described and used in the specification of the
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Common Lisp Object System appearing in chapter <A HREF="node260.html#CLOS">28</A>; this gives
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the flavor of how erroneous situations will be described,
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and appropriate actions prescribed, in the forthcoming ANSI Common
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Lisp standard.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<BR> <HR><A NAME=tex2html1620 HREF="node12.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1618 HREF="node7.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1612 HREF="node10.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html1622 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html1623 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html1621 HREF="node12.html"> Descriptions of Functions </A>
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<B>Up:</B> <A NAME=tex2html1619 HREF="node7.html"> Notational Conventions</A>
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<B> Previous:</B> <A NAME=tex2html1613 HREF="node10.html"> EvaluationExpansion, 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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