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103 lines
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Section 1.4.1.3</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="01_dabc.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="01_da.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="01_dad.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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1.4.1.3 Special Symbols</H2> <P>
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The special symbols described here are used as a notational convenience within this document, and are part of neither the Common Lisp language nor its environment. <P>
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<P><DL><DT>=> <P><DD>
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This indicates evaluation. For example: <P>
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<PRE>
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(+ 4 5) => 9
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</PRE>
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</TT> This means that the result of evaluating the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> <TT>(+ 4 5)</TT> is <TT>9</TT>. <P>
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If a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> returns <A REL=DEFINITION HREF="26_glo_m.htm#multiple_values"><I>multiple values</I></A>, those values might be shown separated by spaces, line breaks, or commas. For example: <P>
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<PRE>
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(truncate 7 5)
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=> 1 2
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(truncate 7 5)
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=> 1
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2
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(truncate 7 5)
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=> 1, 2
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</PRE>
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</TT> <P>
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Each of the above three examples is equivalent, and specifies that <TT>(truncate 7 5)</TT> returns two values, which are <TT>1</TT> and <TT>2</TT>. <P>
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Some <A REL=DEFINITION HREF="26_glo_c.htm#conforming_implementation"><I>conforming implementations</I></A> actually type an arrow (or some other indicator) before showing return values, while others do not. <P>
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<DT>OR=> <P><DD>
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The notation ``OR=> '' is used to denote one of several possible alternate results. The example <P>
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<PRE>
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(char-name #\a)
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=> NIL
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OR=> "LOWERCASE-a"
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OR=> "Small-A"
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OR=> "LA01"
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</PRE>
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</TT> <P>
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indicates that <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, <TT>"LOWERCASE-a"</TT>, <TT>"Small-A"</TT>, <TT>"LA01"</TT> are among the possible results of <TT>(char-name #\a)</TT>---each with equal preference. Unless explicitly specified otherwise, it should not be assumed that the set of possible results shown is exhaustive. Formally, the above example is equivalent to <P>
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<PRE>
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(char-name #\a) => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A>
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</PRE>
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</TT> <P>
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but it is intended to provide additional information to illustrate some of the ways in which it is permitted for implementations to diverge. <P>
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<DT>NOT=> <P><DD>
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The notation ``NOT=> '' is used to denote a result which is not possible. This might be used, for example, in order to emphasize a situation where some anticipated misconception might lead the reader to falsely believe that the result might be possible. For example, <P>
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<PRE>
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(function-lambda-expression
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(funcall #'(lambda (x) #'(lambda () x)) nil))
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=> NIL, <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>, NIL
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OR=> (LAMBDA () X), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>, NIL
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NOT=> NIL, <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>, NIL
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NOT=> (LAMBDA () X), <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>, NIL
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</PRE>
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</TT> <P>
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<DT>== <P><DD>
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This indicates code equivalence. For example: <P>
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<PRE>
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(gcd x (gcd y z)) == (gcd (gcd x y) z)
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</PRE>
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</TT> This means that the results and observable side-effects of evaluating the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> <TT>(gcd x (gcd y z))</TT> are always the same as the results and observable side-effects of <TT>(gcd (gcd x y) z)</TT> for any <TT>x</TT>, <TT>y</TT>, and <TT>z</TT>. <P>
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<DT>>> <P><DD>
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Common Lisp specifies input and output with respect to a non-interactive stream model. The specific details of how interactive input and output are mapped onto that non-interactive model are <A REL=DEFINITION HREF="26_glo_i.htm#implementation-defined"><I>implementation-defined</I></A>. <P>
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For example, <A REL=DEFINITION HREF="26_glo_c.htm#conforming_implementation"><I>conforming implementations</I></A> are permitted to differ in issues of how interactive input is terminated. For example, the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> terminates when the final delimiter is typed on a non-interactive stream. In some <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>, an interactive call to <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> returns as soon as the final delimiter is typed, even if that delimiter is not a <A REL=DEFINITION HREF="26_glo_n.htm#newline"><I>newline</I></A>. In other <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>, a final <A REL=DEFINITION HREF="26_glo_n.htm#newline"><I>newline</I></A> is always required. In still other <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>, there might be a command which ``activates'' a buffer full of input without the command itself being visible on the program's input stream. <P>
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In the examples in this document, the notation ``>> '' precedes lines where interactive input and output occurs. Within such a scenario, ``this notation'' notates user input. <P>
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For example, the notation <P>
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<PRE>
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(+ 1 (print (+ (sqrt (read)) (sqrt (read)))))
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>> 9 16
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>> 7
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=> 8
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</PRE>
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</TT> <P>
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shows an interaction in which ``<TT>(+ 1 (print (+ (sqrt (read)) (sqrt (read)))))</TT>'' is a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> to be <I>evaluated</I>, ``<TT>9 16 </TT>'' is interactive input, ``<TT>7</TT>'' is interactive output, and ``<TT>8</TT>'' is the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> <I>yielded</I> from the <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A>. <P>
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The use of this notation is intended to disguise small differences in interactive input and output behavior between <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>. <P>
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Sometimes, the non-interactive stream model calls for a <A REL=DEFINITION HREF="26_glo_n.htm#newline"><I>newline</I></A>. How that <A REL=DEFINITION HREF="26_glo_n.htm#newline"><I>newline</I></A> character is interactively entered is an <A REL=DEFINITION HREF="26_glo_i.htm#implementation-defined"><I>implementation-defined</I></A> detail of the user interface, but in that case, either the notation ``<Newline>'' or ``<NEWLINE>'' might be used. <P>
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<PRE>
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(progn (format t "~&Who? ") (read-line))
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>> Who? Fred, Mary, and Sally<NEWLINE>
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=> "Fred, Mary, and Sally", <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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</PRE>
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</TT> <P>
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<P></DL><P>
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