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245 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>6.2.2. Specific Data Type Predicates</TITLE>
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<meta name="description" value=" Specific Data Type Predicates">
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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=tex2html2422 HREF="node74.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2420 HREF="node71.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2416 HREF="node72.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2424 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2425 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2423 HREF="node74.html"> Equality Predicates</A>
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<B>Up:</B> <A NAME=tex2html2421 HREF="node71.html"> Data Type Predicates</A>
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<B> Previous:</B> <A NAME=tex2html2417 HREF="node72.html"> General Type Predicates</A>
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<HR> <P>
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<H2><A NAME=SECTION001022000000000000000>6.2.2. Specific Data Type Predicates</A></H2>
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<P>
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The following predicates test for individual data types.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>null</tt> <tt><i>object</i></tt><P>
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<tt>null</tt> is true if its argument is <tt>()</tt>,
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and otherwise is false.
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This is the same operation performed by the function <tt>not</tt>;
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however, <tt>not</tt> is normally used to invert a Boolean value,
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whereas <tt>null</tt> is normally used to test for an empty list. The programmer
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can therefore express <i>intent</i> by the choice of function name.
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<P><pre>
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(null x) == (typep x 'null) == (eq x '<tt>()</tt>)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>symbolp</tt> <tt><i>object</i></tt><P><tt>symbolp</tt> is true if its argument is a symbol,
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and otherwise is false.
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<P><pre>
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(symbolp x) == (typep x 'symbol)
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</pre><P>
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<hr>
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<b>Compatibility note:</b> The Interlisp equivalent of <tt>symbolp</tt> is
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called <tt>litatom</tt>.
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<hr>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>atom</tt> <tt><i>object</i></tt><P>The predicate <tt>atom</tt> is true if its argument is not a cons,
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and otherwise is false.
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Note that <tt>(atom '<tt>()</tt>)</tt> is true, because <tt>()</tt><IMG ALIGN=BOTTOM ALT="" SRC="_24769_tex2html_wrap40411.gif"><tt>nil</tt>.
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<P><pre>
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(atom x) == (typep x 'atom) == (not (typep x 'cons))
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</pre><P>
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<hr>
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<b>Compatibility note:</b> In some Lisp dialects, notably Interlisp,
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only symbols and numbers are considered to be atoms; arrays
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and strings are considered to be neither atoms nor lists (conses).
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<hr>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>consp</tt> <tt><i>object</i></tt><P>The predicate <tt>consp</tt> is true if its argument is a cons,
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and otherwise is false.
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Note that the empty list is not a cons, so
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<tt>(consp '<tt>()</tt>)</tt> == <tt>(consp '<tt>nil</tt>)</tt> => <tt>nil</tt>.
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<P><pre>
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(consp x) == (typep x 'cons) == (not (typep x 'atom))
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</pre><P>
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<hr>
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<b>Compatibility note:</b> Some Lisp implementations call this function
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<tt>pairp</tt> or <tt>listp</tt>. The name <tt>pairp</tt> was rejected for Common Lisp
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because it emphasizes too strongly the dotted-pair notion rather than the
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usual usage of conses in lists. On the other hand, <tt>listp</tt> too strongly
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implies that the cons is in fact part of a list, which after all it might
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not be; moreover, <tt>()</tt> is a list, though not a cons.
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The name <tt>consp</tt> seems to be the appropriate compromise.
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<hr>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>listp</tt> <tt><i>object</i></tt><P><tt>listp</tt> is true if its argument is a cons or the empty list <tt>()</tt>,
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and otherwise is false. It does not check for whether the list
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is a ``true list'' (one terminated by <tt>nil</tt>) or a ``dotted list''
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(one terminated by a non-null atom).
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<P><pre>
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(listp x) == (typep x 'list) == (typep x '(or cons null))
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>numberp</tt> <tt><i>object</i></tt><P><tt>numberp</tt> is true if its argument is any kind of number,
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and otherwise is false.
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<P><pre>
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(numberp x) == (typep x 'number)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>integerp</tt> <tt><i>object</i></tt><P><tt>integerp</tt> is true if its argument is an integer, and otherwise
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is false.
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<P><pre>
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(integerp x) == (typep x 'integer)
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</pre><P>
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<hr>
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<b>Compatibility note:</b> In MacLisp this is called <tt>fixp</tt>.
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Users have been confused as to whether this meant <tt>integerp</tt>
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or <tt>fixnump</tt>, and so the name <tt>integerp</tt> has been adopted here.
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<hr>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>rationalp</tt> <tt><i>object</i></tt><P><tt>rationalp</tt> is true if its argument is a rational number (a ratio or
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an integer), and otherwise is false.
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<P><pre>
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(rationalp x) == (typep x 'rational)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>floatp</tt> <tt><i>object</i></tt><P><tt>floatp</tt> is true if its argument is a floating-point number,
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and otherwise is false.
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<P><pre>
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(floatp x) == (typep x 'float)
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</pre><P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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<BR><b>[Function]</b><BR>
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<tt>realp</tt> <tt><i>object</i></tt><P>X3J13 voted in March 1989 (REAL-NUMBER-TYPE) <A NAME=4196> </A> to add the function <tt>realp</tt>.
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<tt>realp</tt> is true if its argument is a real number,
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and otherwise is false.
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<P><pre>
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(realp x) == (typep x 'real)
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</pre><P>
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<img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR><b>[Function]</b><BR>
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<tt>complexp</tt> <tt><i>object</i></tt><P><tt>complexp</tt> is true if its argument is a complex number,
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and otherwise is false.
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<P><pre>
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(complexp x) == (typep x 'complex)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>characterp</tt> <tt><i>object</i></tt><P><tt>characterp</tt> is true if its argument is a character,
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and otherwise is false.
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<P><pre>
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(characterp x) == (typep x 'character)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>stringp</tt> <tt><i>object</i></tt><P><tt>stringp</tt> is true if its argument is a string,
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and otherwise is false.
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<P><pre>
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(stringp x) == (typep x 'string)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>bit-vector-p</tt> <tt><i>object</i></tt><P><tt>bit-vector-p</tt> is true if its argument is a bit-vector,
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and otherwise is false.
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<P><pre>
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(bit-vector-p x) == (typep x 'bit-vector)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>vectorp</tt> <tt><i>object</i></tt><P><tt>vectorp</tt> is true if its argument is a vector,
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and otherwise is false.
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<P><pre>
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(vectorp x) == (typep x 'vector)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>simple-vector-p</tt> <tt><i>object</i></tt><P><tt>vectorp</tt> is true if its argument is a simple general vector,
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and otherwise is false.
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<P><pre>
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(simple-vector-p x) == (typep x 'simple-vector)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>simple-string-p</tt> <tt><i>object</i></tt><P><tt>simple-string-p</tt> is true if its argument is a simple string,
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and otherwise is false.
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<P><pre>
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(simple-string-p x) == (typep x 'simple-string)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>simple-bit-vector-p</tt> <tt><i>object</i></tt><P><tt>simple-bit-vector-p</tt> is true if its argument is a simple bit-vector,
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and otherwise is false.
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<P><pre>
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(simple-bit-vector-p x) == (typep x 'simple-bit-vector)
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</pre>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>arrayp</tt> <tt><i>object</i></tt><P><tt>arrayp</tt> is true if its argument is an array,
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and otherwise is false.
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<P><pre>
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(arrayp x) == (typep x 'array)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>packagep</tt> <tt><i>object</i></tt><P><tt>packagep</tt> is true if its argument is a package,
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and otherwise is false.
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<P><pre>
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(packagep x) == (typep x 'package)
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</pre><P>
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<BR><b>[Function]</b><BR>
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<tt>functionp</tt> <tt><i>object</i></tt><P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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<tt>functionp</tt> is true if its argument is suitable for applying
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to arguments, using for example the <tt>funcall</tt> or <tt>apply</tt> function.
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Otherwise <tt>functionp</tt> is false.
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<P>
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<tt>functionp</tt> is always true of symbols, lists whose <i>car</i>
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is the symbol <tt>lambda</tt>, any value returned by the <tt>function</tt>
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special form, and any values returned by the function <tt>compile</tt>
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when the first argument is <tt>nil</tt>.
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<br><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 June 1988 (FUNCTION-TYPE) <A NAME=4267> </A>
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to define
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<P><pre>
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(functionp x) == (typep x 'function)
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</pre><P>
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Because the vote also specifies that types <tt>cons</tt> and <tt>symbol</tt> are disjoint
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from the type <tt>function</tt>, this is an incompatible change;
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now <tt>functionp</tt> is in fact always false of symbols and lists.
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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><b>[Function]</b><BR>
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<tt>compiled-function-p</tt> <tt><i>object</i></tt><P><tt>compiled-function-p</tt> is true if its argument is any compiled code object,
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and otherwise is false.
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<P><pre>
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(compiled-function-p x) == (typep x 'compiled-function)
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</pre><P>
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<P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif">
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<BR><b>[Function]</b><BR>
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<tt>commonp</tt> <tt><i>object</i></tt><P><tt>commonp</tt> is true if its argument is any standard Common Lisp data type,
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and otherwise is false.
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<P><pre>
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(commonp x) == (typep x 'common)
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</pre><P>
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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
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(COMMON-TYPE) <A NAME=4289> </A>
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to remove the predicate <tt>commonp</tt> (and the type <tt>common</tt>) from the language.
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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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<P>See also <tt>standard-char-p</tt>, <tt>string-char-p</tt>,
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<tt>streamp</tt>, <tt>random-state-p</tt>,
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<tt>readtablep</tt>,
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<tt>hash-table-p</tt>, and <tt>pathnamep</tt>.
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<P>
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<BR> <HR><A NAME=tex2html2422 HREF="node74.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2420 HREF="node71.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2416 HREF="node72.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2424 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2425 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2423 HREF="node74.html"> Equality Predicates</A>
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|
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<B>Up:</B> <A NAME=tex2html2421 HREF="node71.html"> Data Type Predicates</A>
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|
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<B> Previous:</B> <A NAME=tex2html2417 HREF="node72.html"> General Type Predicates</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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