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36 lines
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<TITLE>CLHS: Section 5.2</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="05_ac.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="05_.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="c_data_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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5.2 Transfer of Control to an Exit Point</H2> <P>
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When a transfer of control is initiated by <A REL=DEFINITION HREF="s_go.htm#go"><B>go</B></A>, <A REL=DEFINITION HREF="s_ret_fr.htm#return-from"><B>return-from</B></A>, or <A REL=DEFINITION HREF="s_throw.htm#throw"><B>throw</B></A> the following events occur in order to accomplish the transfer of control. Note that for <A REL=DEFINITION HREF="s_go.htm#go"><B>go</B></A>, the <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit point</I></A> is the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> within the <A REL=DEFINITION HREF="s_tagbod.htm#tagbody"><B>tagbody</B></A> that is being executed at the time the <A REL=DEFINITION HREF="s_go.htm#go"><B>go</B></A> is performed; for <A REL=DEFINITION HREF="s_ret_fr.htm#return-from"><B>return-from</B></A>, the <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit point</I></A> is the corresponding <A REL=DEFINITION HREF="s_block.htm#block"><B>block</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>; and for <A REL=DEFINITION HREF="s_throw.htm#throw"><B>throw</B></A>, the <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit point</I></A> is the corresponding <A REL=DEFINITION HREF="s_catch.htm#catch"><B>catch</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<P><DL><DT>1. Intervening <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit points</I></A> are ``abandoned'' (i.e., their <A REL=DEFINITION HREF="26_glo_e.htm#extent"><I>extent</I></A> ends and it is no longer valid to attempt to transfer control through them). <P><DD>
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<DT>2. The cleanup clauses of any intervening <A REL=DEFINITION HREF="s_unwind.htm#unwind-protect"><B>unwind-protect</B></A> clauses are evaluated. <P><DD>
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<DT>3. Intervening dynamic <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A> of <A REL=DEFINITION HREF="d_specia.htm#special"><B>special</B></A> variables, <A REL=DEFINITION HREF="26_glo_c.htm#catch_tag"><I>catch tags</I></A>, <A REL=DEFINITION HREF="26_glo_c.htm#condition_handler"><I>condition handlers</I></A>, and <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A> are undone. <P><DD>
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<DT>4. The <A REL=DEFINITION HREF="26_glo_e.htm#extent"><I>extent</I></A> of the <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit point</I></A> being invoked ends, and control is passed to the target. <P><DD></DL><P>
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The extent of an exit being ``abandoned'' because it is being passed over ends as soon as the transfer of control is initiated. That is, event 1 occurs at the beginning of the initiation of the transfer of control. The consequences are undefined if an attempt is made to transfer control to an <A REL=DEFINITION HREF="26_glo_e.htm#exit_point"><I>exit point</I></A> whose <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_extent"><I>dynamic extent</I></A> has ended. <P>
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Events 2 and 3 are actually performed interleaved, in the order corresponding to the reverse order in which they were established. The effect of this is that the cleanup clauses of an <A REL=DEFINITION HREF="s_unwind.htm#unwind-protect"><B>unwind-protect</B></A> see the same dynamic <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>bindings</I></A> of variables and <A REL=DEFINITION HREF="26_glo_c.htm#catch_tag"><I>catch tags</I></A> as were visible when the <A REL=DEFINITION HREF="s_unwind.htm#unwind-protect"><B>unwind-protect</B></A> was entered. <P>
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Event 4 occurs at the end of the transfer of control. <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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