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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: Section 3.4.4</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="03_dc.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_d.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_dda.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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3.4.4 Macro Lambda Lists</H2> <A NAME="AMbody"></A> <A NAME="AMwhole"></A> <A NAME="AMenvironment"></A> <P>
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A <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A> is used in describing <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A> defined by the <A REL=DEFINITION HREF="26_glo_o.htm#operator"><I>operators</I></A> in the next figure. <P>
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<PRE>
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<A REL=DEFINITION HREF="m_define.htm#define-compiler-macro">define-compiler-macro</A> <A REL=DEFINITION HREF="m_defmac.htm#defmacro">defmacro</A> <A REL=DEFINITION HREF="s_flet_.htm#macrolet">macrolet</A>
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<A REL=DEFINITION HREF="m_defi_3.htm#define-setf-expander">define-setf-expander</A>
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</PRE>
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<P><B>Figure 3-17. Operators that use Macro Lambda Lists</B> <P>
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With the additional restriction that an <A REL=DEFINITION HREF="26_glo_e.htm#environment_parameter"><I>environment parameter</I></A> may appear only once (at any of the positions indicated), a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A> has the following syntax: <P>
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<P> <PRE>
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reqvars::= var*
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</PRE>
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<PRE>
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optvars::= [&optional {var | (var [init-form [supplied-p-parameter]])}*]
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</PRE>
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<PRE>
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restvar::= [{&rest | &body} var]
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</PRE>
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<PRE>
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keyvars::= [&key {var | ({var | (keyword-name var)} [init-form [supplied-p-parameter]])}*
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[&allow-other-keys]]
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</PRE>
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<PRE>
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auxvars::= [&aux {var | (var [init-form])}*]
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</PRE>
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<PRE>
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envvar::= [&environment var]
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</PRE>
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<PRE>
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wholevar::= [&whole var]
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</PRE>
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<PRE>
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lambda-list::= (wholevar envvar reqvars envvar optvars envvar
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restvar envvar keyvars envvar auxvars envvar) |
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(wholevar envvar reqvars envvar optvars envvar . var)
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</PRE>
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<PRE>
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pattern::= (wholevar reqvars optvars restvar keyvars auxvars) |
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(wholevar reqvars optvars . var)
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</PRE>
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<P> <P>
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A <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A> can contain the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list_keyword"><I>lambda list keywords</I></A> shown in the next figure. <P>
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<PRE>
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&allow-other-keys &environment &rest
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&aux &key &whole
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&body &optional
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</PRE>
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<P><B>Figure 3-18. Lambda List Keywords used by Macro Lambda Lists</B> <P>
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<A REL=DEFINITION HREF="26_glo_o.htm#optional_parameter"><I>Optional parameters</I></A> (introduced by <TT>&optional</TT>) and <A REL=DEFINITION HREF="26_glo_k.htm#keyword_parameter"><I>keyword parameters</I></A> (introduced by <TT>&key</TT>) can be supplied in a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A>, just as in an <A REL=DEFINITION HREF="26_glo_o.htm#ordinary_lambda_list"><I>ordinary lambda list</I></A>. Both may contain default initialization forms and <A REL=DEFINITION HREF="26_glo_s.htm#supplied-p_parameter"><I>supplied-p parameters</I></A>. <P>
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<TT>&body</TT> is identical in function to <TT>&rest</TT>, but it can be used to inform certain output-formatting and editing functions that the remainder of the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is treated as a body, and should be indented accordingly. Only one of <TT>&body</TT> or <TT>&rest</TT> can be used at any particular level; see <A REL=CHILD HREF="03_dda.htm">Section 3.4.4.1 (Destructuring by Lambda Lists)</A>. <TT>&body</TT> can appear at any level of a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A>; for details, see <A REL=CHILD HREF="03_dda.htm">Section 3.4.4.1 (Destructuring by Lambda Lists)</A>. <P>
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<TT>&whole</TT> is followed by a single variable that is bound to the entire macro-call form; this is the value that the <A REL=DEFINITION HREF="26_glo_m.htm#macro_function"><I>macro function</I></A> receives as its first argument. If <TT>&whole</TT> and a following variable appear, they must appear first in <I>lambda-list</I>, before any other parameter or <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list_keyword"><I>lambda list keyword</I></A>. <TT>&whole</TT> can appear at any level of a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A>. At inner levels, the <TT>&whole</TT> variable is bound to the corresponding part of the argument, as with <TT>&rest</TT>, but unlike <TT>&rest</TT>, other arguments are also allowed. The use of <TT>&whole</TT> does not affect the pattern of arguments specified. <P>
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<TT>&environment</TT> is followed by a single variable that is bound to an <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A> representing the <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> in which the macro call is to be interpreted. This <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A> should be used with <A REL=DEFINITION HREF="f_macro_.htm#macro-function"><B>macro-function</B></A>, <A REL=DEFINITION HREF="f_get_se.htm#get-setf-expansion"><B>get-setf-expansion</B></A>, <A REL=DEFINITION HREF="f_cmp_ma.htm#compiler-macro-function"><B>compiler-macro-function</B></A>, and <A REL=DEFINITION HREF="f_mexp_.htm#macroexpand"><B>macroexpand</B></A> (for example) in computing the expansion of the macro, to ensure that any <A REL=DEFINITION HREF="26_glo_l.htm#lexical_binding"><I>lexical bindings</I></A> or definitions established in the <A REL=DEFINITION HREF="26_glo_c.htm#compilation_environment"><I>compilation environment</I></A> are taken into account. <TT>&environment</TT> can only appear at the top level of a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A>, and can only appear once, but can appear anywhere in that list; the <TT>&environment</TT> <A REL=DEFINITION HREF="26_glo_p.htm#parameter"><I>parameter</I></A> is <A REL=DEFINITION HREF="26_glo_b.htm#bound"><I>bound</I></A> along with <TT>&whole</TT> before any other <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variables</I></A> in the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A>, regardless of where <TT>&environment</TT> appears in the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A>. The <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> that is bound to the <A REL=DEFINITION HREF="26_glo_e.htm#environment_parameter"><I>environment parameter</I></A> has <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_extent"><I>dynamic extent</I></A>. <P>
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Destructuring allows a <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A> to express the structure of a macro call syntax. If no <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list_keyword"><I>lambda list keywords</I></A> appear, then the <A REL=DEFINITION HREF="26_glo_m.htm#macro_lambda_list"><I>macro lambda list</I></A> is a <A REL=DEFINITION HREF="26_glo_t.htm#tree"><I>tree</I></A> containing parameter names at the leaves. The pattern and the <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A> must have compatible <A REL=DEFINITION HREF="26_glo_t.htm#tree_structure"><I>tree structure</I></A>; that is, their <A REL=DEFINITION HREF="26_glo_t.htm#tree_structure"><I>tree structure</I></A> must be equivalent, or it must differ only in that some <A REL=DEFINITION HREF="26_glo_l.htm#leaf"><I>leaves</I></A> of the pattern match <A REL=DEFINITION HREF="26_glo_n.htm#non-atomic"><I>non-atomic</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> of the <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A>. For information about error detection in this <A REL=DEFINITION HREF="26_glo_s.htm#situation"><I>situation</I></A>, see <A REL=CHILD HREF="03_eag.htm">Section 3.5.1.7 (Destructuring Mismatch)</A>. <P>
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A destructuring <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A> (whether at top level or embedded) can be dotted, ending in a parameter name. This situation is treated exactly as if the parameter name that ends the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> had appeared preceded by <TT>&rest</TT>. <P>
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It is permissible for a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> (or a <A REL=DEFINITION HREF="26_glo_s.htm#subexpression"><I>subexpression</I></A> of a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>) to be a <A REL=DEFINITION HREF="26_glo_d.htm#dotted_list"><I>dotted list</I></A> only when <TT>(... &rest var)</TT> or <TT>(... . var)</TT> is used to match it. It is the responsibility of the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> to recognize and deal with such situations. <P>
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<A REL=CHILD HREF="03_dda.htm"><H2>
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3.4.4.1 Destructuring by Lambda Lists</H2></A><P><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/iss139.htm">DOTTED-MACRO-FORMS:ALLOW</A><LI> <A REL=CHILD HREF="../Issues/iss010.htm">ARGUMENT-MISMATCH-ERROR-AGAIN:CONSISTENT</A><LI> <A REL=CHILD HREF="../Issues/iss229.htm">MACRO-ENVIRONMENT-EXTENT:DYNAMIC</A><LI> <A REL=CHILD HREF="../Issues/iss001.htm">&ENVIRONMENT-BINDING-ORDER:FIRST</A><LI> <A REL=CHILD HREF="../Issues/iss101.htm">DEFINE-COMPILER-MACRO:X3J13-NOV89</A><LI> <A REL=CHILD HREF="../Issues/iss342.htm">SYNTACTIC-ENVIRONMENT-ACCESS:RETRACTED-MAR91</A><LI> <A REL=CHILD HREF="../Issues/iss308.htm">SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS</A><LI> <A REL=CHILD HREF="../Issues/iss185.htm">GET-SETF-METHOD-ENVIRONMENT:ADD-ARG</A><LI> <A REL=CHILD HREF="../Issues/iss231.htm">MACRO-FUNCTION-ENVIRONMENT:YES</A><LI> <A REL=CHILD HREF="../Issues/iss106.htm">DEFMACRO-LAMBDA-LIST:TIGHTEN-DESCRIPTION</A><P></UL><HR>
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