111 lines
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111 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>22.4. Querying the User</TITLE>
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<meta name="description" value=" Querying the User">
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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=tex2html4044 HREF="node202.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4042 HREF="node186.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4038 HREF="node200.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4046 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4047 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4045 HREF="node202.html"> File System Interface</A>
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<B>Up:</B> <A NAME=tex2html4043 HREF="node186.html"> Input/Output</A>
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<B> Previous:</B> <A NAME=tex2html4039 HREF="node200.html"> Formatted Output to </A>
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<HR> <P>
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<H1><A NAME=SECTION002640000000000000000>22.4. Querying the User</A></H1>
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<P>
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<A NAME=25365>The</A>
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<A NAME=25366>following</A>
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functions provide a convenient and consistent interface for
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asking questions of the user. Questions are printed and the answers are
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read using the stream <tt>*query-io*</tt>, which normally is synonymous with
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<tt>*terminal-io*</tt> but can be rebound to another stream for special
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applications.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>y-or-n-p &optional <i>format-string</i> &rest <i>arguments</i></tt><P>This predicate is for asking the user a question whose answer is either
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``yes'' or ``no.'' It types out a message (if supplied), reads an answer
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in some implementation-dependent manner (intended to be short and simple,
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like reading a single character such as <tt>Y</tt> or <tt>N</tt>), and is
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true if the answer was ``yes'' or false if the answer was ``no.''
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<P>
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If the <i>format-string</i> argument is supplied and not <tt>nil</tt>,
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then a <tt>fresh-line</tt> operation is performed; then
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a message is printed as if the <i>format-string</i> and <i>arguments</i>
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were given to <tt>format</tt>.
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Otherwise it is assumed that any message has already been printed
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by other means.
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If you want a question mark at the end of the message,
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you must put it there yourself; <tt>y-or-n-p</tt> will not add it.
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However, the message should not contain an explanatory note such
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as <tt>(Y or N)</tt>, because the nature of the interface provided for
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<tt>y-or-n-p</tt> by a given implementation might not involve typing a
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character on a keyboard; <tt>y-or-n-p</tt> will provide such a note
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if appropriate.
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<P>
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All input and output are performed using the stream in the global
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variable <tt>*query-io*</tt>.
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<P>
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Here are some examples of the use of <tt>y-or-n-p</tt>:
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<P><pre>
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(y-or-n-p "Produce listing file?")
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(y-or-n-p "Cannot connect to network host ~S. Retry?" host)
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</pre><P>
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<P>
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<tt>y-or-n-p</tt> should only be used for questions that the user knows
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are coming or in situations where the user is known to be waiting for
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a response of some kind.
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If the user is unlikely to anticipate the question,
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or if the consequences of the answer might be grave and irreparable,
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then <tt>y-or-n-p</tt> should not be used because the user might type ahead
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and thereby accidentally answer the question.
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For such questions as ``Shall I delete all of your files?'' it is better to use
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<tt>yes-or-no-p</tt>.
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<P>
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<br><b>[Function]</b><BR>
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<tt>yes-or-no-p &optional <i>format-string</i> &rest <i>arguments</i></tt><P>This predicate, like <tt>y-or-n-p</tt>, is for asking the user a question
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whose answer is either ``yes'' or ``no.'' It types out a message (if
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supplied), attracts the user's attention (for example, by ringing
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the terminal's bell), and reads a reply in some
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implementation-dependent manner. It is intended that the reply require
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the user to take more action than just a single keystroke, such as typing
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the full word <tt>yes</tt> or <tt>no</tt> followed by a newline.
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<P>
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If the <i>format-string</i> argument is supplied and not <tt>nil</tt>,
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then a <tt>fresh-line</tt> operation is performed; then
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a message is printed as if the <i>format-string</i> and <i>arguments</i>
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were given to <tt>format</tt>.
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Otherwise it is assumed that any message has already been printed
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by other means.
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If you want a question mark at the end of the message,
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you must put it there yourself; <tt>yes-or-no-p</tt> will not add it.
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However, the message should not contain an explanatory note such
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as <tt>(Yes or No)</tt> because the nature of the interface provided for
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<tt>yes-or-no-p</tt> by a given implementation might not involve typing the
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reply on a keyboard; <tt>yes-or-no-p</tt> will provide such a note
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if appropriate.
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<P>
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All input and output are performed using the stream in the global
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variable <tt>*query-io*</tt>.
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<P>
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To allow the user to answer a yes-or-no question with a single
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character, use <tt>y-or-n-p</tt>. <tt>yes-or-no-p</tt> should be
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used for unanticipated or momentous questions;
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this is why it attracts attention
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and why it requires a multiple-action sequence to answer it.
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<P>
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<P>
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<BR> <HR><A NAME=tex2html4044 HREF="node202.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4042 HREF="node186.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4038 HREF="node200.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4046 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4047 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4045 HREF="node202.html"> File System Interface</A>
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<B>Up:</B> <A NAME=tex2html4043 HREF="node186.html"> Input/Output</A>
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<B> Previous:</B> <A NAME=tex2html4039 HREF="node200.html"> Formatted Output to </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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