73 lines
4.7 KiB
HTML
73 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 GO</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="s_catch.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_data_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="s_ret_fr.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="go"><I>Special Operator</I> <B>GO</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>go</B> <I>tag</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>tag</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#go_tag"><I>go tag</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="#go"><B>go</B></A> transfers control to the point in the body of an enclosing <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> form labeled by a tag <A REL=DEFINITION HREF="f_eql.htm#eql"><B>eql</B></A> to <I>tag</I>. If there is no such <I>tag</I> in the body, the bodies of lexically containing <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> (if any) are examined as well. If several tags are <A REL=DEFINITION HREF="f_eql.htm#eql"><B>eql</B></A> to <I>tag</I>, control is transferred to whichever matching <I>tag</I> is contained in the innermost <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> form that contains the <A REL=DEFINITION HREF="#go"><B>go</B></A>. The consequences are undefined if there is no matching <I>tag</I> lexically visible to the point of the <A REL=DEFINITION HREF="#go"><B>go</B></A>. <P>
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The transfer of control initiated by <A REL=DEFINITION HREF="#go"><B>go</B></A> is performed as described in <A REL=CHILD HREF="05_b.htm">Section 5.2 (Transfer of Control to an Exit Point)</A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(tagbody
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(setq val 2)
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(go lp)
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(incf val 3)
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lp (incf val 4)) => NIL
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val => 6
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</PRE>
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</TT> <P>
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<P>
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The following is in error because there is a normal exit of the <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> before the <A REL=DEFINITION HREF="#go"><B>go</B></A> is executed. <P>
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<PRE>
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(let ((a nil))
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(tagbody t (setq a #'(lambda () (go t))))
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(funcall a))
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</PRE>
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</TT> <P>
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The following is in error because the <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> is passed over before the <A REL=DEFINITION HREF="#go"><B>go</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is executed. <P>
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<PRE>
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(funcall (block nil
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(tagbody a (return #'(lambda () (go a))))))
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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_tagbod.htm#tagbody"><B>tagbody</B></A> <P>
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<P><B>Notes:</B> None.
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss152.htm">EXIT-EXTENT:MINIMAL</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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