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124 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: Function MACROEXPAND, MACROEXPAND-1</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_macro_.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_evalua.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_defi_1.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="macroexpand"><A NAME="macroexpand-1"><I>Function</I> <B>MACROEXPAND, MACROEXPAND-1</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>macroexpand</B> <I>form <TT>&optional</TT> env</I> => <I>expansion, expanded-p</I><P>
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<B>macroexpand-1</B> <I>form <TT>&optional</TT> env</I> => <I>expansion, expanded-p</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>form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<I>env</I>---an <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. The default is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>expansion</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<I>expanded-p</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#macroexpand"><B>macroexpand</B></A> and <A REL=DEFINITION HREF="#macroexpand-1"><B>macroexpand-1</B></A> expand <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A>. <P>
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If <I>form</I> is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A>, then <A REL=DEFINITION HREF="#macroexpand-1"><B>macroexpand-1</B></A> expands the <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A> call once. <P>
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<A REL=DEFINITION HREF="#macroexpand"><B>macroexpand</B></A> repeatedly expands <I>form</I> until it is no longer a <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A>. In effect, <A REL=DEFINITION HREF="#macroexpand"><B>macroexpand</B></A> calls <A REL=DEFINITION HREF="#macroexpand-1"><B>macroexpand-1</B></A> repeatedly until the <A REL=DEFINITION HREF="26_glo_s.htm#secondary_value"><I>secondary value</I></A> it returns is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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If <I>form</I> is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A>, then the <I>expansion</I> is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_expansion"><I>macro expansion</I></A> and <I>expanded-p</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>. Otherwise, the <I>expansion</I> is the given <I>form</I> and <I>expanded-p</I> is <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A>. <P>
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Macro expansion is carried out as follows. Once <A REL=DEFINITION HREF="#macroexpand-1"><B>macroexpand-1</B></A> has determined that the <I>form</I> is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A>, it obtains an appropriate expansion <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> for the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> or <A REL=DEFINITION HREF="26_glo_s.htm#symbol_macro"><I>symbol macro</I></A>. The value of <A REL=DEFINITION HREF="v_mexp_h.htm#STmacroexpand-hookST"><B>*macroexpand-hook*</B></A> is coerced to a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> and then called as a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of three arguments: the expansion <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A>, the <I>form</I>, and the <I>env</I>. The <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> returned from this call is taken to be the expansion of the <I>form</I>. <P>
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In addition to <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> definitions in the global environment, any local macro definitions established within <I>env</I> by <A REL=DEFINITION HREF="s_flet_.htm#macrolet"><B>macrolet</B></A> or <A REL=DEFINITION HREF="s_symbol.htm#symbol-macrolet"><B>symbol-macrolet</B></A> are considered. If only <I>form</I> is supplied as an argument, then the environment is effectively null, and only global macro definitions as established by <A REL=DEFINITION HREF="m_defmac.htm#defmacro"><B>defmacro</B></A> are considered. <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>Macro</I></A> definitions are shadowed by local <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> definitions. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(defmacro alpha (x y) `(beta ,x ,y)) => ALPHA
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(defmacro beta (x y) `(gamma ,x ,y)) => BETA
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(defmacro delta (x y) `(gamma ,x ,y)) => EPSILON
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(defmacro expand (form &environment env)
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(multiple-value-bind (expansion expanded-p)
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(macroexpand form env)
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`(values ',expansion ',expanded-p))) => EXPAND
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(defmacro expand-1 (form &environment env)
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(multiple-value-bind (expansion expanded-p)
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(macroexpand-1 form env)
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`(values ',expansion ',expanded-p))) => EXPAND-1
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;; Simple examples involving just the global environment
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(macroexpand-1 '(alpha a b)) => (BETA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(expand-1 (alpha a b)) => (BETA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macroexpand '(alpha a b)) => (GAMMA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(expand (alpha a b)) => (GAMMA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macroexpand-1 'not-a-macro) => NOT-A-MACRO, <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(expand-1 not-a-macro) => NOT-A-MACRO, <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(macroexpand '(not-a-macro a b)) => (NOT-A-MACRO A B), <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(expand (not-a-macro a b)) => (NOT-A-MACRO A B), <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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;; Examples involving lexical environments
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(macrolet ((alpha (x y) `(delta ,x ,y)))
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(macroexpand-1 '(alpha a b))) => (BETA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macrolet ((alpha (x y) `(delta ,x ,y)))
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(expand-1 (alpha a b))) => (DELTA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macrolet ((alpha (x y) `(delta ,x ,y)))
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(macroexpand '(alpha a b))) => (GAMMA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macrolet ((alpha (x y) `(delta ,x ,y)))
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(expand (alpha a b))) => (GAMMA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macrolet ((beta (x y) `(epsilon ,x ,y)))
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(expand (alpha a b))) => (EPSILON A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(let ((x (list 1 2 3)))
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(symbol-macrolet ((a (first x)))
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(expand a))) => (FIRST X), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(let ((x (list 1 2 3)))
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(symbol-macrolet ((a (first x)))
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(macroexpand 'a))) => A, <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(symbol-macrolet ((b (alpha x y)))
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(expand-1 b)) => (ALPHA X Y), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(symbol-macrolet ((b (alpha x y)))
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(expand b)) => (GAMMA X Y), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(symbol-macrolet ((b (alpha x y))
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(a b))
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(expand-1 a)) => B, <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(symbol-macrolet ((b (alpha x y))
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(a b))
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(expand a)) => (GAMMA X Y), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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;; Examples of shadowing behavior
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(flet ((beta (x y) (+ x y)))
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(expand (alpha a b))) => (BETA A B), <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(macrolet ((alpha (x y) `(delta ,x ,y)))
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(flet ((alpha (x y) (+ x y)))
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(expand (alpha a b)))) => (ALPHA A B), <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(let ((x (list 1 2 3)))
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(symbol-macrolet ((a (first x)))
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(let ((a x))
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(expand a)))) => A, <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="m_defmac.htm#defmacro"><B>defmacro</B></A>, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> of <A REL=DEFINITION HREF="f_macro_.htm#macro-function"><B>macro-function</B></A>, <A REL=DEFINITION HREF="s_flet_.htm#macrolet"><B>macrolet</B></A>, <A REL=DEFINITION HREF="s_symbol.htm#symbol-macrolet"><B>symbol-macrolet</B></A> <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="v_mexp_h.htm#STmacroexpand-hookST"><B>*macroexpand-hook*</B></A>, <A REL=DEFINITION HREF="m_defmac.htm#defmacro"><B>defmacro</B></A>, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> of <A REL=DEFINITION HREF="f_macro_.htm#macro-function"><B>macro-function</B></A>, <A REL=DEFINITION HREF="s_flet_.htm#macrolet"><B>macrolet</B></A>, <A REL=DEFINITION HREF="s_symbol.htm#symbol-macrolet"><B>symbol-macrolet</B></A>, <A REL=CHILD HREF="03_a.htm">Section 3.1 (Evaluation)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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Neither <A REL=DEFINITION HREF="#macroexpand"><B>macroexpand</B></A> nor <A REL=DEFINITION HREF="#macroexpand-1"><B>macroexpand-1</B></A> makes any explicit attempt to expand <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro forms</I></A> that are either <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of the <I>form</I> or <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of the <I>expansion</I>. Such expansion might occur implicitly, however, due to the semantics or implementation of the <A REL=DEFINITION HREF="26_glo_m.htm#macro_function"><I>macro function</I></A>. <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/iss179.htm">FUNCTION-TYPE:X3J13-MARCH-88</A><LI> <A REL=CHILD HREF="../Issues/iss235.htm">MACROEXPAND-RETURN-VALUE:TRUE</A><P></UL><HR>
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