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3.7 KiB
HTML
58 lines
3.7 KiB
HTML
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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>B.1. Introduction</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Introduction">
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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=tex2html6238 HREF="node364.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html6236 HREF="node362.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html6230 HREF="node362.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html6240 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html6241 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html6239 HREF="node364.html"> Generators</A>
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<B>Up:</B> <A NAME=tex2html6237 HREF="node362.html"> Generators and Gatherers</A>
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<B> Previous:</B> <A NAME=tex2html6231 HREF="node362.html"> Generators and Gatherers</A>
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<HR> <P>
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<H1><A NAME=SECTION003510000000000000000>B.1. Introduction</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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Generators are generalized input streams in the sense of
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Smalltalk [<A HREF="node368.html#SMALLTALK80BOOK">20</A>]. A generator can produce a potentially
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unbounded number of elements of any type. Individual elements are not
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computed until requested by <tt>next-in</tt>. When an element is taken from
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a generator, it is removed by side effect. Subsequent uses of
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<tt>next-in</tt> obtain later elements.
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<P>
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There is a close relationship between a generator and a series of the
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elements it produces. In particular, any series can be converted into
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a generator. As a result, all the scanner functions used for
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creating series (see appendix <A HREF="node347.html#SERIES">A</A>) can be used to create
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generators as well. There is no need to have a separate
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set of functions for creating generators.
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<P>
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Gatherers are generalized output streams. Elements of any type can be
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entered into a gatherer using <tt>next-out</tt>. The gatherer combines the
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elements together in time-sequence order into a net result. This result can
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be retrieved using <tt>result-of</tt>.
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<P>
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There is a close relationship between a gatherer and a collector function
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that combines elements in the same way. In particular, any one-input
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one-output collector can be converted into a gatherer. As a result, all
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the collectors used for computing summary results from series can be used to
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create gatherers. There is no need to have a separate set of functions for
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creating gatherers.
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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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<BR> <HR><A NAME=tex2html6238 HREF="node364.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html6236 HREF="node362.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html6230 HREF="node362.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html6240 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html6241 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html6239 HREF="node364.html"> Generators</A>
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<B>Up:</B> <A NAME=tex2html6237 HREF="node362.html"> Generators and Gatherers</A>
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<B> Previous:</B> <A NAME=tex2html6231 HREF="node362.html"> Generators and Gatherers</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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