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91 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: Macro PROG1, PROG2</TITLE>
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<A NAME="prog1"><A NAME="prog2"><I>Macro</I> <B>PROG1, PROG2</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>prog1</B> <I>first-form <I>form</I><B>*</B></I> => <I>result-1</I><P>
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<B>prog2</B> <I>first-form second-form <I>form</I><B>*</B></I> => <I>result-2</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>first-form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>; evaluated as described below. <P>
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<I>second-form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>; evaluated as described below. <P>
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<I>forms</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>; evaluated as described below. <P>
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<I>result-1</I>---the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> resulting from the <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A> of <I>first-form</I>. <P>
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<I>result-2</I>---the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> resulting from the <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A> of <I>second-form</I>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#prog1"><B>prog1</B></A> <A REL=DEFINITION HREF="26_glo_e.htm#evaluate"><I>evaluates</I></A> <I>first-form</I> and then <I>forms</I>, <I>yielding</I> as its only <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> <I>yielded</I> by <I>first-form</I>. <P>
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<A REL=DEFINITION HREF="#prog2"><B>prog2</B></A> <A REL=DEFINITION HREF="26_glo_e.htm#evaluate"><I>evaluates</I></A> <I>first-form</I>, then <I>second-form</I>, and then <I>forms</I>, <I>yielding</I> as its only <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> <I>yielded</I> by <I>first-form</I>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(setq temp 1) => 1
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(prog1 temp (print temp) (incf temp) (print temp))
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>> 1
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>> 2
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=> 1
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(prog1 temp (setq temp nil)) => 2
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temp => NIL
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(prog1 (values 1 2 3) 4) => 1
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(setq temp (list 'a 'b 'c))
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(prog1 (car temp) (setf (car temp) 'alpha)) => A
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temp => (ALPHA B C)
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(flet ((swap-symbol-values (x y)
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(setf (symbol-value x)
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(prog1 (symbol-value y)
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(setf (symbol-value y) (symbol-value x))))))
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(let ((*foo* 1) (*bar* 2))
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(declare (special *foo* *bar*))
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(swap-symbol-values '*foo* '*bar*)
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(values *foo* *bar*)))
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=> 2, 1
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(setq temp 1) => 1
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(prog2 (incf temp) (incf temp) (incf temp)) => 3
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temp => 4
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(prog2 1 (values 2 3 4) 5) => 2
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<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_mult_1.htm#multiple-value-prog1"><B>multiple-value-prog1</B></A>, <A REL=DEFINITION HREF="s_progn.htm#progn"><B>progn</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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<A REL=DEFINITION HREF="#prog1"><B>prog1</B></A> and <A REL=DEFINITION HREF="#prog2"><B>prog2</B></A> are typically used to <A REL=DEFINITION HREF="26_glo_e.htm#evaluate"><I>evaluate</I></A> one or more <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> with side effects and return a <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> that must be computed before some or all of the side effects happen. <P>
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<PRE>
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(prog1 form*) == (values (multiple-value-prog1 form*))
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(prog2 form1 form*) == (let () form1 (prog1 form*))
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</PRE>
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</TT> <P>
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