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82 lines
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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>29.4.9. Warnings</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Warnings">
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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=tex2html5980 HREF="node344.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5978 HREF="node334.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5972 HREF="node342.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5982 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5983 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5981 HREF="node344.html"> Restart Functions</A>
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<B>Up:</B> <A NAME=tex2html5979 HREF="node334.html"> Program Interface to </A>
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<B> Previous:</B> <A NAME=tex2html5973 HREF="node342.html"> Finding and Manipulating </A>
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<HR> <P>
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<H2><A NAME=SECTION003349000000000000000>29.4.9. Warnings</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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<A NAME=WARNINGCONDITIONS>Warnings</A>
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are a subclass of errors that are conventionally regarded as ``mild.''
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<P>
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<BR><b>[Function]</b><BR>
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<tt>warn <i>datum</i> &rest <em>arguments</em></tt><P> [This supersedes the description of <tt>warn</tt>
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given in section <A HREF="node220.html#ERRORSIGNALLINGFUNCTIONS">24.1</A>.-GLS]
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<P>
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Warns about a situation, by signaling a condition of type <tt>warning</tt>.
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<P>
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If <i>datum</i> is a condition, then that condition is used directly.
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In this case, if the condition is not of type <tt>warning</tt> or arguments
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is non-<tt>nil</tt>, an error of type <tt>type-error</tt> is signaled.
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<P>
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If <i>datum</i> is a condition type (a class or class name), then the condition used is effectively the result
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of <tt>(apply #'make-condition <i>datum</i> <i>arguments</i>)</tt>. This result
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must be of type <tt>warning</tt> or an error of type <tt>type-error</tt> is signaled.
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<P>
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If <i>datum</i> is a string, then the condition used is effectively the result of
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<P><pre>
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(make-condition 'simple-error
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:format-string <i>datum</i>
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:format-arguments <i>arguments</i>)
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</pre><P>
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<P>
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The precise mechanism for warning is as follows.
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<OL>
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<P>
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<LI> The warning condition is signaled.
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<P>
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While the <tt>warning</tt> condition is being signaled, the <tt>muffle-warning</tt>
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restart is established for use by a handler to bypass further action
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by <tt>warn</tt> (that is, to cause <tt>warn</tt> to immediately return <tt>nil</tt>).
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<P>
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As part of the signaling process, if
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<tt>(typep <i>condition</i> *break-on-signals*)</tt>
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is true, then a <tt>break</tt> will occur prior to beginning the signaling
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process.
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<P>
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<LI> If no handlers for the warning condition are found, or if all such
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handlers decline, then the condition will be reported to <tt>*error-output*</tt>
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by the <tt>warn</tt> function (with possible implementation-specific extra
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output such as motion to a fresh line before or after the display
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of the warning, or supplying some introductory text mentioning
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the name of the function that called <tt>warn</tt> or the fact that this
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is a warning).
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<P>
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<LI> The value returned by <tt>warn</tt> (if it returns) is <tt>nil</tt>.
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</OL>
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<img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR> <HR><A NAME=tex2html5980 HREF="node344.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5978 HREF="node334.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5972 HREF="node342.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5982 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5983 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5981 HREF="node344.html"> Restart Functions</A>
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<B>Up:</B> <A NAME=tex2html5979 HREF="node334.html"> Program Interface to </A>
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<B> Previous:</B> <A NAME=tex2html5973 HREF="node342.html"> Finding and Manipulating </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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