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211 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>11.6. Built-in Packages</TITLE>
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<BODY>
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<meta name="description" value=" Built-in Packages">
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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=tex2html2983 HREF="node118.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2981 HREF="node111.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2975 HREF="node116.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2985 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2986 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2984 HREF="node118.html"> Package System Functions </A>
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<B>Up:</B> <A NAME=tex2html2982 HREF="node111.html"> Packages</A>
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<B> Previous:</B> <A NAME=tex2html2976 HREF="node116.html"> Name Conflicts</A>
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<HR> <P>
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<H1><A NAME=SECTION001560000000000000000>11.6. Built-in Packages</A></H1>
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<P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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The following packages, at least, are built into every Common Lisp system.
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<P>
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<DL COMPACT><DT><tt>lisp</tt>
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<DD>
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The package named <tt>lisp</tt> contains the primitives of the
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Common Lisp system. Its external symbols include all of the
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user-visible functions and global variables that are present in the
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Common Lisp system, such as <tt>car</tt>, <tt>cdr</tt>, and <tt>*package*</tt>.
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Almost all other packages will want to use <tt>lisp</tt> so that these
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symbols will be accessible without qualification.
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<P>
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<DT><tt>user</tt>
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<DD>
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The <tt>user</tt> package is, by default, the current package at the time
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a Common Lisp system starts up. This package uses the <tt>lisp</tt> package.
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</DL>
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<img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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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X3J13 voted in March 1989 (LISP-PACKAGE-NAME) <A NAME=10403> </A> to specify that
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the forthcoming ANSI Common Lisp will use the package name <tt>common-lisp</tt>
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instead of <tt>lisp</tt> and the package name <tt>common-lisp-user</tt>
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instead of <tt>user</tt>. The purpose is to allow a single Lisp system
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to support both ``old'' Common Lisp and ``new'' ANSI Common Lisp
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simultaneously despite the fact that in some cases
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the two languages use the same
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names for incompatible purposes. (That's what packages are for!)
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<P>
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<DL COMPACT><DT><tt>common-lisp</tt>
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<DD>
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The package named <tt>common-lisp</tt> contains the primitives of the
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ANSI Common Lisp system (as opposed to a Common Lisp system based
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on the 1984 specification). Its external symbols include all of the
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user-visible functions and global variables that are present in the
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ANSI Common Lisp system, such as <tt>car</tt>, <tt>cdr</tt>, and <tt>*package*</tt>.
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Note, however, that the home package of such symbols is not
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necessarily the <tt>common-lisp</tt> package (this makes it easier for
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symbols such as <tt>t</tt> and <tt>lambda</tt> to be shared between
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the <tt>common-lisp</tt> package and another package, possibly one named <tt>lisp</tt>).
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Almost all other packages ought to use <tt>common-lisp</tt> so that these
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symbols will be accessible without qualification.
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This package has the nickname <tt>cl</tt>.
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<P>
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<DT><tt>common-lisp-user</tt>
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<DD>
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The <tt>common-lisp-user</tt> package is, by default,
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the current package at the time an ANSI Common Lisp system starts up.
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This package uses the <tt>common-lisp</tt> package
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and has the nickname <tt>cl-user</tt>.
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It may contain other implementation-dependent symbols
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and may use other implementation-specific packages.
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</DL>
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<img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<DL COMPACT><DT><tt>keyword</tt>
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<DD>
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This package contains all of the keywords used by built-in
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or user-defined Lisp functions. Printed symbol representations
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that start with a colon are interpreted as referring to symbols
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in this package, which are always external symbols. All symbols in this
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package are treated as constants that evaluate to themselves, so that the
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user can type <tt>:foo</tt> instead of <tt>':foo</tt>.
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<P>
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</DL>
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<P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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<DL COMPACT><DT><tt>system</tt>
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<DD>
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This package name is reserved to the implementation.
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Normally this is used to contain names of implementation-dependent
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system-interface functions. This package uses <tt>lisp</tt> and has the
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nickname <tt>sys</tt>.
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</DL>
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<img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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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X3J13 voted in January 1989
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(PACKAGE-CLUTTER) <A NAME=10440> </A>
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to modify the requirements on the built-in packages
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so as to limit what may appear in the <tt>common-lisp</tt> package
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and to lift the requirement that every implementation have a package
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named <tt>system</tt>. The details are as follows.
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<P>
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Not only must the <tt>common-lisp</tt> package in any given implementation
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contain all the external symbols prescribed by the standard;
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the <tt>common-lisp</tt> package moreover may not contain any external symbol
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that is not prescribed by the standard. However, the <tt>common-lisp</tt>
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package may contain additional internal symbols, depending on the
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implementation.
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<P>
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An external symbol of the <tt>common-lisp</tt> package may not have a function,
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macro, or special form definition, or a top-level value,
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or a <tt>special</tt> proclamation, or a type definition, unless specifically
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permitted by the standard. Programmers may validly rely on this fact;
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for example, <tt>fboundp</tt> is guaranteed to be false for all
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external symbols of the <tt>common-lisp</tt> package except those explicitly
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specified in the standard to name functions, macros, and special forms.
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Similarly, <tt>boundp</tt> will be false of all such external symbols
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except those documented to be variables or constants.
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<P>
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Portable programs
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may use external symbols in the <tt>common-lisp</tt> package that are not documented
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to be constants or variables as names of local lexical
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variables with the presumption that the implementation has not
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proclaimed such variables to be special; this legitimizes the common
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practice of using such names as <tt>list</tt> and <tt>string</tt> as names
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for local variables.
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<P>
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A valid implementation may initially have properties on any symbol,
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or dynamically put new properties on symbols (even user-created symbols),
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as long as no property indicator used for this purpose is
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an external symbol of any package defined by the standard
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or a symbol that is accessible from the <tt>common-lisp-user</tt> package or any
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package defined by the user.
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<P>
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This vote eliminates the requirement that every implementation have
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a predefined package named <tt>system</tt>. An implementation may
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provide any number of predefined packages; these should be described
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in the documentation for that implementation.
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<P>
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The <tt>common-lisp-user</tt> package may contain symbols not described by the standard
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and may use other implementation-specific packages.
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<P>
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X3J13 voted in March 1989 (LISP-SYMBOL-REDEFINITION) <A NAME=10459> </A>
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to restrict user programs from performing certain actions that
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might interfere with built-in facilities or interact badly
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with them.
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Except where explicitly allowed, the consequences are undefined if any
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of the following actions are performed on a symbol in the <tt>common-lisp</tt>
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package.
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<UL><LI> binding or altering its value (lexically or dynamically)
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<LI> defining or binding it as a function
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<LI> defining or binding it as a macro
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<LI> defining it as a type specifier (<tt>defstruct</tt>, <tt>defclass</tt>, <tt>deftype</tt>)
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<LI> defining it as a structure (<tt>defstruct</tt>)
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<LI> defining it as a declaration
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<LI> dsing it as a symbol macro
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<LI> altering its print name
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<LI> altering its package
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<LI> tracing it
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<LI> declaring or proclaiming it special or lexical
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<LI> declaring or proclaiming its <tt>type</tt> or <tt>ftype</tt>
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<LI> removing it from the package <tt>common-lisp</tt>
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</UL>
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X3J13 also voted in June 1989 (DEFINE-COMPILER-MACRO) <A NAME=10470> </A>
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to add to this list the item
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<UL><LI> defining it as a compiler macro
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</UL>
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<P>
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If such a symbol is not globally defined as a variable or a constant,
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a user program is allowed to lexically bind it and declare the <tt>type</tt> of that binding.
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<P>
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If such a symbol is not defined as a function, macro, or special form,
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a user program is allowed to (lexically) bind it as a function and to declare the
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<tt>ftype</tt> of that binding and to trace that binding.
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<P>
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If such a symbol is not defined as a function, macro, or special form,
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a user program is allowed to (lexically) bind it as a macro.
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<P>
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As an example, the behavior of the code fragment
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<P><pre>
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(flet ((open (filename &key direction)
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(format t "~%OPEN was called.")
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(open filename :direction direction)))
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(with-open-file (x "frob" :direction ':output)
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(format t "~%Was OPEN called?")))
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</pre><P>
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is undefined. Even in a ``reasonable'' implementation,
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for example, the macro expansion of <tt>with-open-file</tt> might refer
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to the <tt>open</tt> function and might not. However, the preceding rules eliminate
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the burden of deciding whether an implementation is reasonable. The code
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fragment violates the rules; officially its behavior is therefore
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completely undefined, and that's that.
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<P>
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Note that ``altering the property list'' is not in the list of
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proscribed actions, so a user program <i>is</i> permitted to
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add properties to or remove properties from
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symbols in the <tt>common-lisp</tt> package.
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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=tex2html2983 HREF="node118.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2981 HREF="node111.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2975 HREF="node116.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2985 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2986 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2984 HREF="node118.html"> Package System Functions </A>
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<B>Up:</B> <A NAME=tex2html2982 HREF="node111.html"> Packages</A>
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<B> Previous:</B> <A NAME=tex2html2976 HREF="node116.html"> Name Conflicts</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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