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58 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>26.12.1. Data Types</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Data Types">
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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=tex2html4700 HREF="node252.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html4698 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html4692 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html4702 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html4703 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html4701 HREF="node252.html"> Destructuring</A>
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<B>Up:</B> <A NAME=tex2html4699 HREF="node250.html"> Miscellaneous Features</A>
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<B> Previous:</B> <A NAME=tex2html4693 HREF="node250.html"> Miscellaneous Features</A>
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<HR> <P>
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<H2><A NAME=SECTION0030121000000000000000>26.12.1. Data Types</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=LOOPTYPESSECTION>Many</A>
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loop constructs take a <i>type-spec</i> argument that
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allows you to specify certain data types for loop variables.
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While it is not necessary to specify a data type for any variable,
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by doing so you ensure that the variable has a correctly typed initial
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value. The type declaration is made available to the compiler for
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more efficient <tt>loop</tt>
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expansion.
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In some implementations,
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fixnum and float declarations are especially
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useful; the compiler notices them and emits more efficient code.
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<P>
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The <i>type-spec</i> argument has the following syntax:
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<PRE>
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<i>type-spec</i> ::= <tt>of-type</tt> <i>d-type-spec</i>
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<i>d-type-spec</i> ::= <i>type-specifier</i> | <tt>(<i>d-type-spec</i> . <i>d-type-spec</i>)</tt>
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</PRE>
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A <i>type-specifier</i> in this syntax can be any Common Lisp type
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specifier. The <i>d-type-spec</i> argument is used for destructuring,
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as described in section <A HREF="node252.html#LOOPDESTRUCTURINGSECTION">26.12.2</A>. If the
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<i>d-type-spec</i> argument consists solely of the types <tt>fixnum</tt>,
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<tt>float</tt>, <tt>t</tt>, or <tt>nil</tt>, the <tt>of-type</tt> keyword is optional. The
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<tt>of-type</tt> construct is optional in these cases to provide backward
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compatibility; thus the following two expressions are the same:
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<P>
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<P><pre>
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;;; This expression uses the old syntax for type specifiers.
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(loop for i fixnum upfrom 3 ...) <BR><BR>;;; This expression uses the new syntax for type specifiers.
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(loop for i of-type fixnum upfrom 3 ...)
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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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