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>define-symbol-macro | Common Lisp Nova Spec</TITLE
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TR
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="define-symbol-macro"
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></SPAN
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><B
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>define-symbol-macro</B
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Macro</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Syntax</B
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></DT
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><DD
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><DIV CLASS="DefmacWithValuesNewline"
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><DIV
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><B
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>define-symbol-macro</B
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> <SPAN CLASS="cmssi"
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>symbol</SPAN
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> <SPAN CLASS="cmssi"
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>expansion</SPAN
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> </DIV
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><DIV
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><SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> <SPAN CLASS="cmssi"
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>symbol</SPAN
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></DIV
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></DIV
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></DD
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><DT
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><B
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>Arguments and Values</B
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></DT
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><DD
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><P CLASS="j"
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><VAR CLASS="param"
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>symbol</VAR
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> — a <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>expansion</VAR
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> — a <A HREF="26_1_Glossary.html#form"
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><EM CLASS="term"
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>form</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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>Provides a mechanism for globally affecting the <A HREF="26_1_Glossary.html#macro_expansion"
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><EM CLASS="term"
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>macro expansion</EM
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></A
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> of the indicated <VAR CLASS="param"
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>symbol</VAR
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>. </P
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><P CLASS="j"
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>Globally establishes an expansion function for the <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> named by <VAR CLASS="param"
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>symbol</VAR
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>. The only guaranteed property of an expansion <A HREF="26_1_Glossary.html#function"
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><EM CLASS="term"
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>function</EM
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></A
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> for a <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> is that when it is applied to the <A HREF="26_1_Glossary.html#form"
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><EM CLASS="term"
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>form</EM
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></A
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> and the <A HREF="26_1_Glossary.html#environment"
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><EM CLASS="term"
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>environment</EM
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></A
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> it returns the correct expansion. (In particular, it is <A HREF="26_1_Glossary.html#implementation-dependent"
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><EM CLASS="term"
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>implementation-dependent</EM
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></A
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> whether the expansion is conceptually stored in the expansion function, the <A HREF="26_1_Glossary.html#environment"
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><EM CLASS="term"
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>environment</EM
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></A
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>, or both.) </P
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><P CLASS="j"
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>Each global reference to <VAR CLASS="param"
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>symbol</VAR
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> (<I CLASS="i"
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><I
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>i.e.</I
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></I
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>, not <A HREF="26_1_Glossary.html#shadow"
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><EM CLASS="term"
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>shadowed</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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> by a <A HREF="26_1_Glossary.html#binding"
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><EM CLASS="term"
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>binding</EM
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></A
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> for a <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> or <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> named by the same <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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>) is expanded by the normal macro expansion process; see <A HREF="3_1_Evaluation.html#sec_3_1_2_1_1" CLASS="secref"
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><SPAN CLASS="cmr"
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>Section</SPAN
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> <SPAN CLASS="cmr"
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>3.1.2.1.1</SPAN
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> <SPAN CLASS="cmr"
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>(Symbols</SPAN
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> <SPAN CLASS="cmr"
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>as</SPAN
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> <SPAN CLASS="cmr"
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>Forms)</SPAN
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></A
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>. The expansion of a <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> is subject to further <A HREF="26_1_Glossary.html#macro_expansion"
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><EM CLASS="term"
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>macro expansion</EM
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></A
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> in the same <A HREF="26_1_Glossary.html#lexical_environment"
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><EM CLASS="term"
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>lexical environment</EM
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></A
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> as the <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> reference, exactly analogous to normal <A HREF="26_1_Glossary.html#macro"
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><EM CLASS="term"
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>macros</EM
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></A
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>. </P
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><P CLASS="j"
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>The consequences are unspecified if a <A HREF="m_special.html" CLASS="declref"
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><B
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>special</B
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></A
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> declaration is made for <VAR CLASS="param"
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>symbol</VAR
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> while in the scope of this definition (<I CLASS="i"
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><I
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>i.e.</I
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></I
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>, when it is not <A HREF="26_1_Glossary.html#shadow"
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><EM CLASS="term"
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>shadowed</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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> by a <A HREF="26_1_Glossary.html#binding"
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><EM CLASS="term"
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>binding</EM
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></A
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> for a <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> or <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> named by the same <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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>). </P
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><P CLASS="j"
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>Any use of <A HREF="f_setq.html" CLASS="specref"
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><B
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>setq</B
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></A
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> to set the value of the <VAR CLASS="param"
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>symbol</VAR
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> while in the scope of this definition is treated as if it were a <A HREF="f_setf.html" CLASS="macref"
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><B
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>setf</B
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></A
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>. <A HREF="f_psetq.html" CLASS="macref"
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><B
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>psetq</B
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></A
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> of <VAR CLASS="param"
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>symbol</VAR
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> is treated as if it were a <A HREF="f_setf.html" CLASS="macref"
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><B
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>psetf</B
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></A
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>, and <A HREF="f_multiple-value-setq.html" CLASS="macref"
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><B
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>multiple-value-setq</B
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></A
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> is treated as if it were a <A HREF="f_setf.html" CLASS="macref"
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><B
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>setf</B
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></A
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> of <A HREF="f_values.html" CLASS="funref"
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><B
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>values</B
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></A
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>. </P
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><P CLASS="j"
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>A <A HREF="26_1_Glossary.html#binding"
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><EM CLASS="term"
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>binding</EM
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></A
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> for a <A HREF="26_1_Glossary.html#symbol_macro"
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><EM CLASS="term"
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>symbol macro</EM
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></A
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> can be <A HREF="26_1_Glossary.html#shadow"
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><EM CLASS="term"
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>shadowed</EM
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></A
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><SPAN CLASS="meaning"
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><SUB CLASS="sub"
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><SPAN CLASS="cmr"
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>2</SPAN
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></SUB
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></SPAN
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> by <A HREF="f_let.html" CLASS="specref"
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><B
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>let</B
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></A
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> or <A HREF="f_symbol-macrolet.html" CLASS="specref"
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><B
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>symbol-macrolet</B
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></A
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>.</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
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><DD
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><PRE CLASS="screen"
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>(defvar *things* (list 'alpha 'beta 'gamma)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> *THINGS*
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(define-symbol-macro thing1 (first *things*)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> THING1
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(define-symbol-macro thing2 (second *things*)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> THING2
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(define-symbol-macro thing3 (third *things*)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> THING3
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thing1 <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> ALPHA
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(setq thing1 'ONE) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> ONE
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*things* <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> (ONE BETA GAMMA)
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(multiple-value-setq (thing2 thing3) (values 'two 'three)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> TWO
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thing3 <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> THREE
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*things* <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> (ONE TWO THREE)
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(list thing2 (let ((thing2 2)) thing2)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> (TWO 2)</PRE
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></DD
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><DT
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><B
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>Exceptional Situations</B
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></DT
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><DD
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><P CLASS="j"
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>If <VAR CLASS="param"
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>symbol</VAR
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> is already defined as a <A HREF="26_1_Glossary.html#global_variable"
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><EM CLASS="term"
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>global variable</EM
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></A
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>, an error of <A HREF="26_1_Glossary.html#type"
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><EM CLASS="term"
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>type</EM
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></A
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> <A HREF="t_program-error.html" CLASS="typeref"
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><B
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>program-error</B
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></A
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> is signaled.</P
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></DD
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><DT
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><B
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>See Also</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="f_symbol-macrolet.html" CLASS="specref"
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><B
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>symbol-macrolet</B
|
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></A
|
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>, <A HREF="f_macroexpand.html" CLASS="funref"
|
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><B
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>macroexpand</B
|
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></A
|
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></P
|
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></DD
|
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></DL
|
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></DIV
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><DIV CLASS="footer"
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><DIV CLASS="btmnav"
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><A HREF="f_macroexpand.html" CLASS="prev"
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>←</A
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>→</A
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>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
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