326 lines
6.5 KiB
HTML
326 lines
6.5 KiB
HTML
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<!DOCTYPE HTML>
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<HTML LANG="en-us"
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>psetq | Common Lisp Nova Spec</TITLE
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><LINK REL="up" HREF="5_3_Data_and_Control_Flow_Dictionary.html" TYPE="text/html" TITLE="5.3 Data and Control Flow Dictionary"
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><SPAN CLASS="breadcrumb-item"
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><A HREF="index.html"
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>Common Lisp Nova Spec</A
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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="5_Data_and_Control_Flow.html"
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>5. Data and Control Flow</A
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></SPAN
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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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></SPAN
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="f_psetq.html"
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>psetq</A
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></SPAN
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><DIV CLASS="apropos-io"
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><A HREF="f_setq.html" CLASS="prev"
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>←</A
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><SPAN ID="apropos-label"
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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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></DIV
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><DIV CLASS="matter"
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><DIV CLASS="com"
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><HR
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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="psetq"
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></SPAN
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><B
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>psetq</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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></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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><P CLASS="j"
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><B
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>psetq</B
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> {↓<VAR CLASS="param"
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>pair</VAR
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>}* <SPAN CLASS="arrow"
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>→</SPAN
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> <SPAN CLASS="misc"
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><B
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>nil</B
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></SPAN
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></P
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><TABLE CELLSPACING="0" CELLPADDING="0" RULES="GROUPS" STYLE="margin: 1ex 0"
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><TBODY
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><TR
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><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE=";padding-right:3px"
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></TD
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><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;padding-right:3px"
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><VAR CLASS="param"
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>pair</VAR
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><SPAN CLASS="cmssi"
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>::</SPAN
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><SPAN CLASS="cmr"
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>=</SPAN
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></TD
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><TD ALIGN="LEFT" VALIGN="BASELINE" STYLE="padding-left:3px;"
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> <SPAN CLASS="cmssi"
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>var</SPAN
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> <SPAN CLASS="cmssi"
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>form</SPAN
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></TD
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></TR
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></TBODY
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></TABLE
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></DD
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><DT
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><B
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>Pronunciation</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_psetq.html" CLASS="macref"
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><B
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>psetq</B
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></A
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>: [ <B CLASS="b"
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>pē set kyü</B
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> ]</P
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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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>var</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#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> other than a <A HREF="26_1_Glossary.html#constant_variable"
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><EM CLASS="term"
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>constant variable</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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>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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>Assigns values to <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variables</EM
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></A
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>. </P
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><P CLASS="j"
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>This is just like <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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>, except that the assignments happen “in parallel.” That is, first all of the forms are evaluated, and only then are the variables set to the resulting values. In this way, the assignment to one variable does not affect the value computation of another in the way that would occur with <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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>’s sequential assignment. </P
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><P CLASS="j"
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>If any <VAR CLASS="param"
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>var</VAR
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> refers to 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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> made by <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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>, then that <VAR CLASS="param"
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>var</VAR
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> is treated as if <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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> (not <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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>) had been used.</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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> ;; A simple use of PSETQ to establish values for variables.
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;; As a matter of style, many programmers would prefer SETQ
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;; in a simple situation like this where parallel assignment
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;; is not needed, but the two have equivalent effect.
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(psetq a 1 b 2 c 3) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> NIL
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a <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 1
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b <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 2
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c <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3
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;; Use of PSETQ to update values by parallel assignment.
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;; The effect here is very different than if SETQ had been used.
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(psetq a (1+ b) b (1+ a) c (+ a b)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> NIL
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a <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3
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b <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 2
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c <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3
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;; Use of PSETQ on a symbol macro.
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(let ((x (list 10 20 30)))
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(symbol-macrolet ((y (car x)) (z (cadr x)))
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(psetq y (1+ z) z (1+ y))
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(list x y z)))
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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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> ((21 11 30) 21 11)
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;; Use of parallel assignment to swap values of A and B.
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(let ((a 1) (b 2))
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(psetq a b b a)
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(values a b))
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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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> 2, 1</PRE
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></DD
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><DT
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><B
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>Side Effects</B
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></DT
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><DD
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><P CLASS="j"
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>The values of <VAR CLASS="param"
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>forms</VAR
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> are assigned to <VAR CLASS="param"
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>vars</VAR
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>.</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_setf.html" CLASS="macref"
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><B
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>psetf</B
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></A
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>, <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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></P
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></DD
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></DL
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></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_setq.html" CLASS="prev"
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>←</A
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><A HREF="f_block.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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></DIV
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><SCRIPT
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>domReady();</SCRIPT
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>
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