794 lines
17 KiB
HTML
794 lines
17 KiB
HTML
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<HTML LANG="en-us"
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>defsetf | Common Lisp Nova Spec</TITLE
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>Common Lisp Nova Spec</A
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> <SPAN CLASS="breadcrumb-item"
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="5_3_Data_and_Control_Flow_Dictionary.html"
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>5.3 Data and Control Flow Dictionary</A
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>defsetf</A
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>←</A
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>Apropos </SPAN
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><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
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></SPAN
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><B
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>defsetf</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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><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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><P CLASS="j"
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>The “short form”:</P
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><DIV CLASS="DefmacWithValuesNewline"
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><DIV
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><B
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>defsetf</B
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> <SPAN CLASS="cmssi"
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>access-fn</SPAN
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> <SPAN CLASS="cmssi"
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>update-fn</SPAN
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> <SPAN CLASS="cmr"
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>[</SPAN
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><SPAN CLASS="cmssi"
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>documentation</SPAN
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><SPAN CLASS="cmr"
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>]</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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>access-fn</SPAN
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></DIV
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></DIV
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><P CLASS="j"
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>The “long form”:</P
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><DIV CLASS="DefmacWithValuesNewline"
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><DIV
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><B
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>defsetf</B
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> <SPAN CLASS="cmssi"
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>access-fn</SPAN
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> <SPAN CLASS="cmssi"
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>lambda-list</SPAN
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> <SPAN CLASS="cmr"
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>(</SPAN
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><SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>store-variable</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*)</SPAN
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> <SPAN CLASS="cmr"
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>⟦ </SPAN
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><SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>declaration</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*</SPAN
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> <SPAN CLASS="cmsy"
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>|</SPAN
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> <VAR CLASS="param"
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>documentation</VAR
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> <SPAN CLASS="cmr"
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> ⟧</SPAN
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> <SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>form</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*</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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>access-fn</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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>access-fn</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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> which names a <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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> or a <A HREF="26_1_Glossary.html#macro"
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><EM CLASS="term"
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>macro</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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>update-fn</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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> naming a <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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> or <A HREF="26_1_Glossary.html#macro"
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><EM CLASS="term"
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>macro</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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>lambda-list</VAR
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> — a <A HREF="26_1_Glossary.html#defsetf_lambda_list"
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><EM CLASS="term"
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>defsetf lambda list</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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>store-variable</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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> (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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> <A HREF="26_1_Glossary.html#name"
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><EM CLASS="term"
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>name</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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>declaration</VAR
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> — a <A HREF="m_declare.html" CLASS="misc"
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><B
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>declare</B
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></A
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> <A HREF="26_1_Glossary.html#expression"
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><EM CLASS="term"
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>expression</EM
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></A
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>; not evaluated. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>documentation</VAR
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> — a <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>string</EM
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></A
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>; not evaluated. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>form</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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><A HREF="f_defsetf.html" CLASS="macref"
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><B
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>defsetf</B
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></A
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> defines how to <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 <A HREF="26_1_Glossary.html#place"
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><EM CLASS="term"
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>place</EM
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></A
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> of the form <CODE CLASS="f"
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>(<I CLASS="i"
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><I
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>access-fn</I
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></I
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> ...)</CODE
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> for relatively simple cases. (See <A HREF="f_define-setf-expander.html" CLASS="macref"
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><B
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>define-setf-expander</B
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></A
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> for more general access to this facility.) It must be the case that the <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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> or <A HREF="26_1_Glossary.html#macro"
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><EM CLASS="term"
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>macro</EM
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></A
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> named by <VAR CLASS="param"
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>access-fn</VAR
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> evaluates all of its arguments. </P
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><P CLASS="j"
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><A HREF="f_defsetf.html" CLASS="macref"
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><B
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>defsetf</B
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></A
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> may take one of two forms, called the “short form” and the “long form,” which are distinguished by the <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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> of the second <A HREF="26_1_Glossary.html#argument"
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><EM CLASS="term"
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>argument</EM
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></A
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>. </P
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><P CLASS="j"
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>When the short form is used, <VAR CLASS="param"
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>update-fn</VAR
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> must name a <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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> (or <A HREF="26_1_Glossary.html#macro"
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><EM CLASS="term"
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>macro</EM
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></A
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>) that takes one more argument than <VAR CLASS="param"
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>access-fn</VAR
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> takes. When <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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> is given a <A HREF="26_1_Glossary.html#place"
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><EM CLASS="term"
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>place</EM
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></A
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> that is a call on <VAR CLASS="param"
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>access-fn</VAR
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>, it expands into a call on <VAR CLASS="param"
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>update-fn</VAR
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> that is given all the arguments to <VAR CLASS="param"
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>access-fn</VAR
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> and also, as its last argument, the new value (which must be returned by <VAR CLASS="param"
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>update-fn</VAR
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> as its value). </P
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><P CLASS="j"
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>The long form <A HREF="f_defsetf.html" CLASS="macref"
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><B
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>defsetf</B
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></A
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> resembles <A HREF="f_defmacro.html" CLASS="macref"
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><B
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>defmacro</B
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></A
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>. The <VAR CLASS="param"
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>lambda-list</VAR
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> describes the arguments of <VAR CLASS="param"
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>access-fn</VAR
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>. The <VAR CLASS="param"
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>store-variables</VAR
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> describe the value or values to be stored into the <A HREF="26_1_Glossary.html#place"
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><EM CLASS="term"
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>place</EM
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></A
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>. The <VAR CLASS="param"
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>body</VAR
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> must compute the expansion of 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 call on <VAR CLASS="param"
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>access-fn</VAR
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>. The expansion function is defined 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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> in which the <A HREF="f_defsetf.html" CLASS="macref"
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><B
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>defsetf</B
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||
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></A
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> <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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> appears. </P
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||
|
|
><P CLASS="j"
|
||
|
|
>During the evaluation of the <VAR CLASS="param"
|
||
|
|
>forms</VAR
|
||
|
|
>, the variables in the <VAR CLASS="param"
|
||
|
|
>lambda-list</VAR
|
||
|
|
> and the <VAR CLASS="param"
|
||
|
|
>store-variables</VAR
|
||
|
|
> are bound to names of temporary variables, generated as if by <A HREF="f_gensym.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>gensym</B
|
||
|
|
></A
|
||
|
|
> or <A HREF="f_gentemp.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>gentemp</B
|
||
|
|
></A
|
||
|
|
>, that will be bound by the expansion of <A HREF="f_setf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>setf</B
|
||
|
|
></A
|
||
|
|
> to the values of those <A HREF="26_1_Glossary.html#subform"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>subforms</EM
|
||
|
|
></A
|
||
|
|
>. This binding permits the <VAR CLASS="param"
|
||
|
|
>forms</VAR
|
||
|
|
> to be written without regard for order-of-evaluation issues. <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> arranges for the temporary variables to be optimized out of the final result in cases where that is possible. </P
|
||
|
|
><P CLASS="j"
|
||
|
|
>The body code in <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> is implicitly enclosed in a <A HREF="26_1_Glossary.html#block"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>block</EM
|
||
|
|
></A
|
||
|
|
> whose name is <VAR CLASS="param"
|
||
|
|
>access-fn</VAR
|
||
|
|
> </P
|
||
|
|
><P CLASS="j"
|
||
|
|
><A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> ensures that <A HREF="26_1_Glossary.html#subform"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>subforms</EM
|
||
|
|
></A
|
||
|
|
> of the <A HREF="26_1_Glossary.html#place"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>place</EM
|
||
|
|
></A
|
||
|
|
> are evaluated exactly once. </P
|
||
|
|
><P CLASS="j"
|
||
|
|
><VAR CLASS="param"
|
||
|
|
>Documentation</VAR
|
||
|
|
> is attached to <VAR CLASS="param"
|
||
|
|
>access-fn</VAR
|
||
|
|
> as a <A HREF="26_1_Glossary.html#documentation_string"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>documentation string</EM
|
||
|
|
></A
|
||
|
|
> of kind <A HREF="f_setf.html" CLASS="misc"
|
||
|
|
><B
|
||
|
|
>setf</B
|
||
|
|
></A
|
||
|
|
>. </P
|
||
|
|
><P CLASS="j"
|
||
|
|
>If a <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> <A HREF="26_1_Glossary.html#form"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>form</EM
|
||
|
|
></A
|
||
|
|
> appears as a <A HREF="26_1_Glossary.html#top_level_form"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>top level form</EM
|
||
|
|
></A
|
||
|
|
>, the <A HREF="26_1_Glossary.html#compiler"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>compiler</EM
|
||
|
|
></A
|
||
|
|
> must make the <A HREF="26_1_Glossary.html#setf_expander"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>setf expander</EM
|
||
|
|
></A
|
||
|
|
> available so that it may be used to expand calls to <A HREF="f_setf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>setf</B
|
||
|
|
></A
|
||
|
|
> later on in the <A HREF="26_1_Glossary.html#file"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>file</EM
|
||
|
|
></A
|
||
|
|
>. Users must ensure that the <VAR CLASS="param"
|
||
|
|
>forms</VAR
|
||
|
|
>, if any, can be evaluated at compile time if the <VAR CLASS="param"
|
||
|
|
>access-fn</VAR
|
||
|
|
> is used in a <A HREF="26_1_Glossary.html#place"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>place</EM
|
||
|
|
></A
|
||
|
|
> later in the same <A HREF="26_1_Glossary.html#file"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>file</EM
|
||
|
|
></A
|
||
|
|
>. The <A HREF="26_1_Glossary.html#compiler"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>compiler</EM
|
||
|
|
></A
|
||
|
|
> must make these <A HREF="26_1_Glossary.html#setf_expander"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>setf expanders</EM
|
||
|
|
></A
|
||
|
|
> available to compile-time calls to <A HREF="f_get-setf-expansion.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>get-setf-expansion</B
|
||
|
|
></A
|
||
|
|
> when its <VAR CLASS="param"
|
||
|
|
>environment</VAR
|
||
|
|
> argument is a value received as the <A HREF="26_1_Glossary.html#environment_parameter"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>environment parameter</EM
|
||
|
|
></A
|
||
|
|
> of a <A HREF="26_1_Glossary.html#macro"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>macro</EM
|
||
|
|
></A
|
||
|
|
>.</P
|
||
|
|
></DD
|
||
|
|
><DT
|
||
|
|
><B
|
||
|
|
>Examples</B
|
||
|
|
></DT
|
||
|
|
><DD
|
||
|
|
><P CLASS="j"
|
||
|
|
>The effect of</P
|
||
|
|
><PRE CLASS="screen"
|
||
|
|
>(defsetf symbol-value set)</PRE
|
||
|
|
><P CLASS="j"
|
||
|
|
>is built into the Common Lisp system. This causes the form <CODE CLASS="f"
|
||
|
|
>(setf (symbol-value foo) fu)</CODE
|
||
|
|
> to expand into <CODE CLASS="f"
|
||
|
|
>(set foo fu)</CODE
|
||
|
|
>. </P
|
||
|
|
><P CLASS="j"
|
||
|
|
>Note that</P
|
||
|
|
><PRE CLASS="screen"
|
||
|
|
>(defsetf car rplaca)</PRE
|
||
|
|
><P CLASS="j"
|
||
|
|
>would be incorrect because <A HREF="f_rplaca.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>rplaca</B
|
||
|
|
></A
|
||
|
|
> does not return its last argument.</P
|
||
|
|
><PRE CLASS="screen"
|
||
|
|
>(defun middleguy (x) (nth (truncate (1- (list-length x)) 2) x)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> MIDDLEGUY
|
||
|
|
(defun set-middleguy (x v)
|
||
|
|
(unless (null x)
|
||
|
|
(rplaca (nthcdr (truncate (1- (list-length x)) 2) x) v))
|
||
|
|
v) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> SET-MIDDLEGUY
|
||
|
|
(defsetf middleguy set-middleguy) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> MIDDLEGUY
|
||
|
|
(setq a (list 'a 'b 'c 'd)
|
||
|
|
b (list 'x)
|
||
|
|
c (list 1 2 3 (list 4 5 6) 7 8 9)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> (1 2 3 (4 5 6) 7 8 9)
|
||
|
|
(setf (middleguy a) 3) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 3
|
||
|
|
(setf (middleguy b) 7) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 7
|
||
|
|
(setf (middleguy (middleguy c)) 'middleguy-symbol) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> MIDDLEGUY-SYMBOL
|
||
|
|
a <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> (A 3 C D)
|
||
|
|
b <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> (7)
|
||
|
|
c <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> (1 2 3 (4 MIDDLEGUY-SYMBOL 6) 7 8 9)</PRE
|
||
|
|
><P CLASS="j"
|
||
|
|
>An example of the use of the long form of <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
>:</P
|
||
|
|
><PRE CLASS="screen"
|
||
|
|
>(defsetf subseq (sequence start &optional end) (new-sequence)
|
||
|
|
`(progn (replace ,sequence ,new-sequence
|
||
|
|
:start1 ,start :end1 ,end)
|
||
|
|
,new-sequence)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> SUBSEQ</PRE
|
||
|
|
><PRE CLASS="screen"
|
||
|
|
> (defvar *xy* (make-array '(10 10)))
|
||
|
|
(defun xy (&key ((x x) 0) ((y y) 0)) (aref *xy* x y)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> XY
|
||
|
|
(defun set-xy (new-value &key ((x x) 0) ((y y) 0))
|
||
|
|
(setf (aref *xy* x y) new-value)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> SET-XY
|
||
|
|
(defsetf xy (&key ((x x) 0) ((y y) 0)) (store)
|
||
|
|
`(set-xy ,store 'x ,x 'y ,y)) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> XY
|
||
|
|
(get-setf-expansion '(xy a b))
|
||
|
|
<SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> (#:t0 #:t1),
|
||
|
|
(a b),
|
||
|
|
(#:store),
|
||
|
|
((lambda (&key ((x #:x)) ((y #:y)))
|
||
|
|
(set-xy #:store 'x #:x 'y #:y))
|
||
|
|
#:t0 #:t1),
|
||
|
|
(xy #:t0 #:t1)
|
||
|
|
(xy 'x 1) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> NIL
|
||
|
|
(setf (xy 'x 1) 1) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 1
|
||
|
|
(xy 'x 1) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 1
|
||
|
|
(let ((a 'x) (b 'y))
|
||
|
|
(setf (xy a 1 b 2) 3)
|
||
|
|
(setf (xy b 5 a 9) 14))
|
||
|
|
<SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 14
|
||
|
|
(xy 'y 0 'x 1) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 1
|
||
|
|
(xy 'x 1 'y 2) <SPAN CLASS="cmsy"
|
||
|
|
><SPAN CLASS="arrow"
|
||
|
|
>→</SPAN
|
||
|
|
></SPAN
|
||
|
|
> 3</PRE
|
||
|
|
></DD
|
||
|
|
><DT
|
||
|
|
><B
|
||
|
|
>See Also</B
|
||
|
|
></DT
|
||
|
|
><DD
|
||
|
|
><P CLASS="j"
|
||
|
|
><A HREF="f_documentation.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>documentation</B
|
||
|
|
></A
|
||
|
|
>, <A HREF="f_setf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>setf</B
|
||
|
|
></A
|
||
|
|
>, <A HREF="f_define-setf-expander.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>define-setf-expander</B
|
||
|
|
></A
|
||
|
|
>, <A HREF="f_get-setf-expansion.html" CLASS="funref"
|
||
|
|
><B
|
||
|
|
>get-setf-expansion</B
|
||
|
|
></A
|
||
|
|
>, <A HREF="5_1_Generalized_Reference.html#sec_5_1" CLASS="secref"
|
||
|
|
><SPAN CLASS="cmr"
|
||
|
|
>Section</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>5.1</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>(Generalized</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>Reference)</SPAN
|
||
|
|
></A
|
||
|
|
>, <A HREF="3_4_Lambda_Lists.html#sec_3_4_11" CLASS="secref"
|
||
|
|
><SPAN CLASS="cmr"
|
||
|
|
>Section</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>3.4.11</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>(Syntactic</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>Interaction</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>of</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>Documentation</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>Strings</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>and</SPAN
|
||
|
|
> <SPAN CLASS="cmr"
|
||
|
|
>Declarations)</SPAN
|
||
|
|
></A
|
||
|
|
></P
|
||
|
|
></DD
|
||
|
|
><DT
|
||
|
|
><B
|
||
|
|
>Notes</B
|
||
|
|
></DT
|
||
|
|
><DD
|
||
|
|
><P CLASS="j"
|
||
|
|
><VAR CLASS="param"
|
||
|
|
>forms</VAR
|
||
|
|
> must include provision for returning the correct value (the value or values of <VAR CLASS="param"
|
||
|
|
>store-variable</VAR
|
||
|
|
>). This is handled by <VAR CLASS="param"
|
||
|
|
>forms</VAR
|
||
|
|
> rather than by <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> because in many cases this value can be returned at no extra cost, by calling a function that simultaneously stores into the <A HREF="26_1_Glossary.html#place"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>place</EM
|
||
|
|
></A
|
||
|
|
> and returns the correct value. </P
|
||
|
|
><P CLASS="j"
|
||
|
|
>A <A HREF="f_setf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>setf</B
|
||
|
|
></A
|
||
|
|
> of a call on <VAR CLASS="param"
|
||
|
|
>access-fn</VAR
|
||
|
|
> also evaluates all of <VAR CLASS="param"
|
||
|
|
>access-fn</VAR
|
||
|
|
>’s arguments; it cannot treat any of them specially. This means that <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> cannot be used to describe how to store into a <A HREF="26_1_Glossary.html#generalized_reference"
|
||
|
|
><EM CLASS="term"
|
||
|
|
>generalized reference</EM
|
||
|
|
></A
|
||
|
|
> to a byte, such as <CODE CLASS="f"
|
||
|
|
>(ldb field reference)</CODE
|
||
|
|
>. <A HREF="f_define-setf-expander.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>define-setf-expander</B
|
||
|
|
></A
|
||
|
|
> is used to handle situations that do not fit the restrictions imposed by <A HREF="f_defsetf.html" CLASS="macref"
|
||
|
|
><B
|
||
|
|
>defsetf</B
|
||
|
|
></A
|
||
|
|
> and gives the user additional control.</P
|
||
|
|
></DD
|
||
|
|
></DL
|
||
|
|
></DIV
|
||
|
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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_define-modify-macro.html" CLASS="prev"
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>←</A
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><A HREF="f_define-setf-expander.html" CLASS="next"
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>→</A
|
||
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></DIV
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><DIV CLASS="trail"
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>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
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