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100 lines
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Macro DEFUN</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="f_apply.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_data_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_fdefin.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="defun"><I>Macro</I> <B>DEFUN</B></A> <P>
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<P>
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<P><B>Syntax:</B><P>
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<P>
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<B>defun</B> <I>function-name lambda-list [[<I>declaration</I><B>*</B> | <I>documentation</I>]] <I>form</I><B>*</B></I><P> => <I>function-name</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>function-name</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function name</I></A>. <P>
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<I>lambda-list</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#ordinary_lambda_list"><I>ordinary lambda list</I></A>. <P>
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<I>declaration</I>---a <A REL=DEFINITION HREF="s_declar.htm#declare"><B>declare</B></A> <A REL=DEFINITION HREF="26_glo_e.htm#expression"><I>expression</I></A>; not evaluated. <P>
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<I>documentation</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>; not evaluated. <P>
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<I>forms</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>. <P>
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<I>block-name</I>---the <A REL=DEFINITION HREF="26_glo_f.htm#function_block_name"><I>function block name</I></A> of the <I>function-name</I>. <P>
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<P><B>Description:</B><P>
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<P>
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Defines a new <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> named <I>function-name</I> in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A>. The body of the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> defined by <A REL=DEFINITION HREF="#defun"><B>defun</B></A> consists of <I>forms</I>; they are executed as an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A> when the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> is called. <A REL=DEFINITION HREF="#defun"><B>defun</B></A> can be used to define a new <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>, to install a corrected version of an incorrect definition, to redefine an already-defined <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>, or to redefine a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> as a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>. <P>
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<A REL=DEFINITION HREF="#defun"><B>defun</B></A> implicitly puts a <A REL=DEFINITION HREF="s_block.htm#block"><B>block</B></A> named <I>block-name</I> around the body <I>forms</I> (but not the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> in the <I>lambda-list</I>) of the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> defined. <P>
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<I>Documentation</I> is attached as a <A REL=DEFINITION HREF="26_glo_d.htm#documentation_string"><I>documentation string</I></A> to <I>name</I> (as kind <A REL=DEFINITION HREF="s_fn.htm#function"><B>function</B></A>) and to the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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Evaluating <A REL=DEFINITION HREF="#defun"><B>defun</B></A> causes <I>function-name</I> to be a global name for the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> specified by the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_expression"><I>lambda expression</I></A> <P>
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<PRE>
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(lambda lambda-list
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</TT>[[<TT></TT><I>declaration</I><TT></TT><B>*</B><TT> </TT>|<TT> </TT><I>documentation</I><TT></TT>]]<TT>
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(block block-name form*))
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</PRE>
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</TT> <P>
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processed in the <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> in which <A REL=DEFINITION HREF="#defun"><B>defun</B></A> was executed. <P>
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(None of the arguments are evaluated at macro expansion time.) <P>
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<A REL=DEFINITION HREF="#defun"><B>defun</B></A> is not required to perform any compile-time side effects. In particular, <A REL=DEFINITION HREF="#defun"><B>defun</B></A> does not make the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> definition available at compile time. An <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> may choose to store information about the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> for the purposes of compile-time error-checking (such as checking the number of arguments on calls), or to enable the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> to be expanded inline. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(defun recur (x)
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(when (> x 0)
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(recur (1- x)))) => RECUR
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(defun ex (a b &optional c (d 66) &rest keys &key test (start 0))
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(list a b c d keys test start)) => EX
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(ex 1 2) => (1 2 NIL 66 NIL NIL 0)
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(ex 1 2 3 4 :test 'equal :start 50)
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=> (1 2 3 4 (:TEST EQUAL :START 50) EQUAL 50)
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(ex :test 1 :start 2) => (:TEST 1 :START 2 NIL NIL 0)
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;; This function assumes its callers have checked the types of the
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;; arguments, and authorizes the compiler to build in that assumption.
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(defun discriminant (a b c)
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(declare (number a b c))
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"Compute the discriminant for a quadratic equation."
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(- (* b b) (* 4 a c))) => DISCRIMINANT
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(discriminant 1 2/3 -2) => 76/9
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;; This function assumes its callers have not checked the types of the
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;; arguments, and performs explicit type checks before making any assumptions.
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(defun careful-discriminant (a b c)
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"Compute the discriminant for a quadratic equation."
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(check-type a number)
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(check-type b number)
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(check-type c number)
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(locally (declare (number a b c))
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(- (* b b) (* 4 a c)))) => CAREFUL-DISCRIMINANT
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(careful-discriminant 1 2/3 -2) => 76/9
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="s_flet_.htm#flet"><B>flet</B></A>, <A REL=DEFINITION HREF="s_flet_.htm#labels"><B>labels</B></A>, <A REL=DEFINITION HREF="s_block.htm#block"><B>block</B></A>, <A REL=DEFINITION HREF="s_ret_fr.htm#return-from"><B>return-from</B></A>, <A REL=DEFINITION HREF="s_declar.htm#declare"><B>declare</B></A>, <A REL=DEFINITION HREF="f_docume.htm#documentation"><B>documentation</B></A>, <A REL=CHILD HREF="03_a.htm">Section 3.1 (Evaluation)</A>, <A REL=CHILD HREF="03_da.htm">Section 3.4.1 (Ordinary Lambda Lists)</A>, <A REL=CHILD HREF="03_dk.htm">Section 3.4.11 (Syntactic Interaction of Documentation Strings and Declarations)</A> <P>
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<P><B>Notes:</B><P>
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<A REL=DEFINITION HREF="s_ret_fr.htm#return-from"><B>return-from</B></A> can be used to return prematurely from a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> defined by <A REL=DEFINITION HREF="#defun"><B>defun</B></A>. <P>
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Additional side effects might take place when additional information (typically debugging information) about the function definition is recorded. <P>
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss059.htm">COMPILE-FILE-HANDLING-OF-TOP-LEVEL-FORMS:CLARIFY</A><LI> <A REL=CHILD HREF="../Issues/iss135.htm">DOCUMENTATION-FUNCTION-BUGS:FIX</A><LI> <A REL=CHILD HREF="../Issues/iss105.htm">DEFMACRO-BLOCK-SCOPE:EXCLUDES-BINDINGS</A><LI> <A REL=CHILD HREF="../Issues/iss174.htm">FUNCTION-NAME:LARGE</A><LI> <A REL=CHILD HREF="../Issues/iss097.htm">DECLS-AND-DOC</A><P></UL><HR>
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