66 lines
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66 lines
4.8 KiB
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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: Special Operator PROGV</TITLE>
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<A NAME="progv"><I>Special Operator</I> <B>PROGV</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>progv</B> <I><I>symbols</I> <I>values</I> <I>form</I><B>*</B></I> => <I><I>result</I><B>*</B></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>symbols</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A>; evaluated. <P>
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<I>values</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A>; evaluated. <P>
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<I>forms</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>. <P>
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<I>results</I>---the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>values</I></A> returned by the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</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="#progv"><B>progv</B></A> creates new dynamic variable <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A> and executes each <I>form</I> using those <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A>. Each <I>form</I> is evaluated in order. <P>
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<A REL=DEFINITION HREF="#progv"><B>progv</B></A> allows <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> one or more dynamic variables whose names may be determined at run time. Each <I>form</I> is evaluated in order with the dynamic variables whose names are in <I>symbols</I> bound to corresponding <I>values</I>. If too few <I>values</I> are supplied, the remaining <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A> are bound and then made to have no value. If too many <I>values</I> are supplied, the excess values are ignored. The <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A> of the dynamic variables are undone on exit from <A REL=DEFINITION HREF="#progv"><B>progv</B></A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(setq *x* 1) => 1
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(progv '(*x*) '(2) *x*) => 2
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*x* => 1
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Assuming *x* is not globally special,
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(let ((*x* 3))
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(progv '(*x*) '(4)
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(list *x* (symbol-value '*x*)))) => (3 4)
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B> None.
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<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="s_let_l.htm#let"><B>let</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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Among other things, <A REL=DEFINITION HREF="#progv"><B>progv</B></A> is useful when writing interpreters for languages embedded in Lisp; it provides a handle on the mechanism for <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variables</I></A>. <P>
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