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167 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: Special Operator FLET, LABELS, MACROLET</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_fmakun.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_funcal.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="flet"><A NAME="labels"><A NAME="macrolet"><I>Special Operator</I> <B>FLET, LABELS, MACROLET</B></A></A></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>flet</B> <I>((<I>function-name</I> <I>lambda-list</I> [[<I>local-declaration</I><B>*</B> | <I>local-documentation</I>]] <I>local-form</I><B>*</B>)<B>*</B>) <I>declaration</I><B>*</B> <I>form</I><B>*</B></I><P> => <I><I>result</I><B>*</B></I><P>
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<P>
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<B>labels</B> <I>((<I>function-name</I> <I>lambda-list</I> [[<I>local-declaration</I><B>*</B> | <I>local-documentation</I>]] <I>local-form</I><B>*</B>)<B>*</B>) <I>declaration</I><B>*</B> <I>form</I><B>*</B></I><P> => <I><I>result</I><B>*</B></I><P>
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<P>
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<B>macrolet</B> <I>((<I>name</I> <I>lambda-list</I> [[<I>local-declaration</I><B>*</B> | <I>local-documentation</I>]] <I>local-form</I><B>*</B>)<B>*</B>) <I>declaration</I><B>*</B> <I>form</I><B>*</B></I><P> => <I><I>result</I><B>*</B></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>name</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. <P>
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<I>lambda-list</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A>; for <A REL=DEFINITION HREF="#flet"><B>flet</B></A> and <A REL=DEFINITION HREF="#labels"><B>labels</B></A>, it is an <A REL=DEFINITION HREF="26_glo_o.htm#ordinary_lambda_list"><I>ordinary lambda list</I></A>; for <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A>, it is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A>. <P>
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<I>local-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>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>local-documentation</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>; not evaluated. <P>
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<I>local-forms</I>, <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>results</I>---the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>values</I></A> of the <I>forms</I>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#flet"><B>flet</B></A>, <A REL=DEFINITION HREF="#labels"><B>labels</B></A>, and <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> define local <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> and <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A>, and execute <I>forms</I> using the local definitions. <I>Forms</I> are executed in order of occurrence. <P>
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The body forms (but not the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A>) of each <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> created by <A REL=DEFINITION HREF="#flet"><B>flet</B></A> and <A REL=DEFINITION HREF="#labels"><B>labels</B></A> and each <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> created by <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> are enclosed in an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_block"><I>implicit block</I></A> whose name is the <A REL=DEFINITION HREF="26_glo_f.htm#function_block_name"><I>function block name</I></A> of the <I>function-name</I> or <I>name</I>, as appropriate. <P>
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The scope of the <I>declarations</I> between the list of local function/macro definitions and the body <I>forms</I> in <A REL=DEFINITION HREF="#flet"><B>flet</B></A> and <A REL=DEFINITION HREF="#labels"><B>labels</B></A> does not include the bodies of the locally defined <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A>, except that for <A REL=DEFINITION HREF="#labels"><B>labels</B></A>, any <A REL=DEFINITION HREF="d_inline.htm#inline"><B>inline</B></A>, <A REL=DEFINITION HREF="d_inline.htm#notinline"><B>notinline</B></A>, or <A REL=DEFINITION HREF="d_ftype.htm#ftype"><B>ftype</B></A> declarations that refer to the locally defined functions do apply to the local function bodies. That is, their <A REL=DEFINITION HREF="26_glo_s.htm#scope"><I>scope</I></A> is the same as the function name that they affect. The scope of these <I>declarations</I> does not include the bodies of the macro expander functions defined by <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A>. <P>
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<P><DL><DT><B>flet</B> <P><DD>
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<A REL=DEFINITION HREF="#flet"><B>flet</B></A> defines locally named <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> and executes a series of <I>forms</I> with these definition <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A>. Any number of such local <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> can be defined. <P>
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The <A REL=DEFINITION HREF="26_glo_s.htm#scope"><I>scope</I></A> of the name <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> encompasses only the body. Within the body of <A REL=DEFINITION HREF="#flet"><B>flet</B></A>, <I>function-names</I> matching those defined by <A REL=DEFINITION HREF="#flet"><B>flet</B></A> refer to the locally defined <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> rather than to the global function definitions of the same name. Also, within the scope of <A REL=DEFINITION HREF="#flet"><B>flet</B></A>, global <A REL=DEFINITION HREF="26_glo_s.htm#setf_expander"><I>setf expander</I></A> definitions of the <I>function-name</I> defined by <A REL=DEFINITION HREF="#flet"><B>flet</B></A> do not apply. Note that this applies to <TT>(defsetf </TT><I>f</I><TT> ...)</TT>, not <TT>(defmethod (setf </TT><I>f</I><TT>) ...)</TT>. <P>
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The names of <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> defined by <A REL=DEFINITION HREF="#flet"><B>flet</B></A> are in the <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A>; they retain their local definitions only within the body of <A REL=DEFINITION HREF="#flet"><B>flet</B></A>. The function definition bindings are visible only in the body of <A REL=DEFINITION HREF="#flet"><B>flet</B></A>, not the definitions themselves. Within the function definitions, local function names that match those being defined refer to <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> or <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A> defined outside the <A REL=DEFINITION HREF="#flet"><B>flet</B></A>. <A REL=DEFINITION HREF="#flet"><B>flet</B></A> can locally <A REL=DEFINITION HREF="26_glo_s.htm#shadow"><I>shadow</I></A> a global function name, and the new definition can refer to the global definition. <P>
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Any <I>local-documentation</I> is attached to the corresponding local <I>function</I> (if one is actually created) as a <A REL=DEFINITION HREF="26_glo_d.htm#documentation_string"><I>documentation string</I></A>. <P>
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<DT><B>labels</B> <P><DD>
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<A REL=DEFINITION HREF="#labels"><B>labels</B></A> is equivalent to <A REL=DEFINITION HREF="#flet"><B>flet</B></A> except that the scope of the defined function names for <A REL=DEFINITION HREF="#labels"><B>labels</B></A> encompasses the function definitions themselves as well as the body. <P>
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<DT><B>macrolet</B> <P><DD>
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<A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> establishes local <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> definitions, using the same format used by <A REL=DEFINITION HREF="m_defmac.htm#defmacro"><B>defmacro</B></A>. <P>
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Within the body of <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A>, global <A REL=DEFINITION HREF="26_glo_s.htm#setf_expander"><I>setf expander</I></A> definitions of the <I>names</I> defined by the <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> do not apply; rather, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> expands the <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A> and recursively process the resulting <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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The macro-expansion functions defined by <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> are defined in the <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> in which the <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> form appears. Declarations and <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> and <A REL=DEFINITION HREF="s_symbol.htm#symbol-macrolet"><B>symbol-macrolet</B></A> definitions affect the local macro definitions in a <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A>, but the consequences are undefined if the local macro definitions reference any local <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> or <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A> that are visible in that <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A>. <P>
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Any <I>local-documentation</I> is attached to the corresponding local <I>macro function</I> as a <A REL=DEFINITION HREF="26_glo_d.htm#documentation_string"><I>documentation string</I></A>. <P>
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<P></DL><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 foo (x flag)
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(macrolet ((fudge (z)
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;The parameters x and flag are not accessible
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; at this point; a reference to flag would be to
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; the global variable of that name.
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` (if flag (* ,z ,z) ,z)))
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;The parameters x and flag are accessible here.
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(+ x
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(fudge x)
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(fudge (+ x 1)))))
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==
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(defun foo (x flag)
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(+ x
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(if flag (* x x) x)
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(if flag (* (+ x 1) (+ x 1)) (+ x 1))))
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</PRE>
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</TT> after macro expansion. The occurrences of <TT>x</TT> and <TT>flag</TT> legitimately refer to the parameters of the function <TT>foo</TT> because those parameters are visible at the site of the macro call which produced the expansion. <P>
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<P>
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<PRE>
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(flet ((flet1 (n) (+ n n)))
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(flet ((flet1 (n) (+ 2 (flet1 n))))
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(flet1 2))) => 6
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(defun dummy-function () 'top-level) => DUMMY-FUNCTION
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(funcall #'dummy-function) => TOP-LEVEL
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(flet ((dummy-function () 'shadow))
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(funcall #'dummy-function)) => SHADOW
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(eq (funcall #'dummy-function) (funcall 'dummy-function))
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=> <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(flet ((dummy-function () 'shadow))
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(eq (funcall #'dummy-function)
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(funcall 'dummy-function)))
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=> <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(defun recursive-times (k n)
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(labels ((temp (n)
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(if (zerop n) 0 (+ k (temp (1- n))))))
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(temp n))) => RECURSIVE-TIMES
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(recursive-times 2 3) => 6
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(defmacro mlets (x &environment env)
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(let ((form `(babbit ,x)))
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(macroexpand form env))) => MLETS
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(macrolet ((babbit (z) `(+ ,z ,z))) (mlets 5)) => 10
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</PRE>
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</TT> <P>
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<PRE>
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(flet ((safesqrt (x) (sqrt (abs x))))
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;; The safesqrt function is used in two places.
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(safesqrt (apply #'+ (map 'list #'safesqrt '(1 2 3 4 5 6)))))
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=> 3.291173
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</PRE>
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</TT> <P>
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<PRE>
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(defun integer-power (n k)
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(declare (integer n))
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(declare (type (integer 0 *) k))
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(labels ((expt0 (x k a)
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(declare (integer x a) (type (integer 0 *) k))
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(cond ((zerop k) a)
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((evenp k) (expt1 (* x x) (floor k 2) a))
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(t (expt0 (* x x) (floor k 2) (* x a)))))
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(expt1 (x k a)
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(declare (integer x a) (type (integer 0 *) k))
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(cond ((evenp k) (expt1 (* x x) (floor k 2) a))
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(t (expt0 (* x x) (floor k 2) (* x a))))))
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(expt0 n k 1))) => INTEGER-POWER
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</PRE>
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</TT> <P>
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<PRE>
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(defun example (y l)
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(flet ((attach (x)
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(setq l (append l (list x)))))
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(declare (inline attach))
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(dolist (x y)
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(unless (null (cdr x))
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(attach x)))
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l))
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(example '((a apple apricot) (b banana) (c cherry) (d) (e))
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'((1) (2) (3) (4 2) (5) (6 3 2)))
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=> ((1) (2) (3) (4 2) (5) (6 3 2) (A APPLE APRICOT) (B BANANA) (C CHERRY))
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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_declar.htm#declare"><B>declare</B></A>, <A REL=DEFINITION HREF="m_defmac.htm#defmacro"><B>defmacro</B></A>, <A REL=DEFINITION HREF="m_defun.htm#defun"><B>defun</B></A>, <A REL=DEFINITION HREF="f_docume.htm#documentation"><B>documentation</B></A>, <A REL=DEFINITION HREF="s_let_l.htm#let"><B>let</B></A>, <A REL=CHILD HREF="03_a.htm">Section 3.1 (Evaluation)</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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<P>
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It is not possible to define recursive <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> with <A REL=DEFINITION HREF="#flet"><B>flet</B></A>. <A REL=DEFINITION HREF="#labels"><B>labels</B></A> can be used to define mutually recursive <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A>. <P>
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If a <A REL=DEFINITION HREF="#macrolet"><B>macrolet</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is a <A REL=DEFINITION HREF="26_glo_t.htm#top_level_form"><I>top level form</I></A>, the body <I>forms</I> are also processed as <A REL=DEFINITION HREF="26_glo_t.htm#top_level_form"><I>top level forms</I></A>. See <A REL=CHILD HREF="03_bc.htm">Section 3.2.3 (File Compilation)</A>. <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/iss214.htm">LISP-SYMBOL-REDEFINITION:MAR89-X3J13</A><LI> <A REL=CHILD HREF="../Issues/iss104.htm">DEFINING-MACROS-NON-TOP-LEVEL:ALLOW</A><LI> <A REL=CHILD HREF="../Issues/iss185.htm">GET-SETF-METHOD-ENVIRONMENT:ADD-ARG</A><LI> <A REL=CHILD HREF="../Issues/iss308.htm">SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS</A><LI> <A REL=CHILD HREF="../Issues/iss092.htm">DECLARATION-SCOPE:NO-HOISTING</A><LI> <A REL=CHILD HREF="../Issues/iss159.htm">FLET-DECLARATIONS</A><LI> <A REL=CHILD HREF="../Issues/iss105.htm">DEFMACRO-BLOCK-SCOPE:EXCLUDES-BINDINGS</A><LI> <A REL=CHILD HREF="../Issues/iss161.htm">FLET-IMPLICIT-BLOCK:YES</A><LI> <A REL=CHILD HREF="../Issues/iss174.htm">FUNCTION-NAME:LARGE</A><LI> <A REL=CHILD HREF="../Issues/iss160.htm">FLET-DECLARATIONS:ALLOW</A><LI> <A REL=CHILD HREF="../Issues/iss097.htm">DECLS-AND-DOC</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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