48 lines
2.4 KiB
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48 lines
2.4 KiB
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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>B.2. Generators</TITLE>
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<meta name="description" value=" Generators">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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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=tex2html6250 HREF="node365.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html6248 HREF="node362.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html6242 HREF="node363.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html6252 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html6253 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html6251 HREF="node365.html"> Gatherers</A>
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<B>Up:</B> <A NAME=tex2html6249 HREF="node362.html"> Generators and Gatherers</A>
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<B> Previous:</B> <A NAME=tex2html6243 HREF="node363.html"> Introduction</A>
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<HR> <P>
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<H1><A NAME=SECTION003520000000000000000>B.2. Generators</A></H1>
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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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These functions create and process generators.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>generator <i>series</i></tt><P>Given a series, <tt>generator</tt> returns a generator containing the same
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elements.
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<P>
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<BR><b>[Macro]</b><BR>
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<tt>next-in <i>generator</i> {<i>action</i>}*</tt><P><tt>next-in</tt> returns the next element in the generator <i>generator</i>.
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The <i>actions</i> can be any Lisp expressions. They are evaluated if and
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only if no more elements can be retrieved from <i>generator</i>. If there
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are no more elements and no actions, it is an error. It is also an error
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to apply <tt>next-in</tt> to a generator a second time after the generator has
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run out of elements. As an example of generators, consider the following.
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<P><pre>
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(let ((x (generator (scan '(1 2 3 4)))))
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(with-output-to-string (s)
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(loop (prin1 (next-in x (return)) s)
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(prin1 (next-in x (return)) s)
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(princ "," s))))
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=> "12,34,"
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</pre><P>
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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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<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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