64 lines
4.7 KiB
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64 lines
4.7 KiB
HTML
<!-- 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 PROGN</TITLE>
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<A NAME="progn"><I>Special Operator</I> <B>PROGN</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>progn</B> <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>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> of 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="#progn"><B>progn</B></A> evaluates <I>forms</I>, in the order in which they are given. <P>
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The values of each <I>form</I> but the last are discarded. <P>
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If <A REL=DEFINITION HREF="#progn"><B>progn</B></A> appears as a <A REL=DEFINITION HREF="26_glo_t.htm#top_level_form"><I>top level form</I></A>, then all <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> within that <A REL=DEFINITION HREF="#progn"><B>progn</B></A> are considered by the compiler to be <A REL=DEFINITION HREF="26_glo_t.htm#top_level_form"><I>top level forms</I></A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(progn) => NIL
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(progn 1 2 3) => 3
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(progn (values 1 2 3)) => 1, 2, 3
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(setq a 1) => 1
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(if a
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(progn (setq a nil) 'here)
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(progn (setq a t) 'there)) => HERE
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a => NIL
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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="m_prog1c.htm#prog1"><B>prog1</B></A>, <A REL=DEFINITION HREF="m_prog1c.htm#prog2"><B>prog2</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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Many places in Common Lisp involve syntax that uses <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progns</I></A>. That is, part of their syntax allows many <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> to be written that are to be evaluated sequentially, discarding the results of all <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> but the last and returning the results of the last <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. Such places include, but are not limited to, the following: the body of a <A REL=DEFINITION HREF="26_glo_l.htm#lambda_expression"><I>lambda expression</I></A>; the bodies of various control and conditional <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> (e.g., <A REL=DEFINITION HREF="m_case_.htm#case"><B>case</B></A>, <A REL=DEFINITION HREF="s_catch.htm#catch"><B>catch</B></A>, <A REL=DEFINITION HREF="#progn"><B>progn</B></A>, and <A REL=DEFINITION HREF="m_when_.htm#when"><B>when</B></A>). <P>
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