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38 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: Section 3.1.2.1.1.2</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="03_abaaa.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_abaa.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_abaac.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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3.1.2.1.1.2 Dynamic Variables</H2> <P>
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A <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> is a <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> if one of the following conditions hold: <P>
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<P><UL><P>
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<LI> It is locally declared or globally proclaimed <A REL=DEFINITION HREF="d_specia.htm#special"><B>special</B></A>. <P>
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<LI> It occurs textually within a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that creates a <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_binding"><I>dynamic binding</I></A> for a <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> of the <A REL=DEFINITION HREF="26_glo_s.htm#same"><I>same</I></A> <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A>, and the <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> is not <I>shadowed</I>[2] by a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that creates a <A REL=DEFINITION HREF="26_glo_l.htm#lexical_binding"><I>lexical binding</I></A> of the same <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A>. <P>
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<P></UL><P>
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A <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> can be referenced at any time in any <A REL=DEFINITION HREF="26_glo_p.htm#program"><I>program</I></A>; there is no textual limitation on references to <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variables</I></A>. At any given time, all <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variables</I></A> with a given name refer to exactly one <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A>, either in the <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_environment"><I>dynamic environment</I></A> or in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A>. <P>
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The <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> part of the <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> for a <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> might be empty; in this case, the <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> is said to have no <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A>, or to be <A REL=DEFINITION HREF="26_glo_u.htm#unbound"><I>unbound</I></A>. A <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> can be made <A REL=DEFINITION HREF="26_glo_u.htm#unbound"><I>unbound</I></A> by using <A REL=DEFINITION HREF="f_makunb.htm#makunbound"><B>makunbound</B></A>. <P>
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The effect of <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> a <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> is to create a new <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> to which all references to that <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> in any <A REL=DEFINITION HREF="26_glo_p.htm#program"><I>program</I></A> refer for the duration of the <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A> of the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that creates the <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_binding"><I>dynamic binding</I></A>. <P>
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A <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> can be referenced outside the <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_extent"><I>dynamic extent</I></A> of a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that <A REL=DEFINITION HREF="26_glo_b.htm#bind"><I>binds</I></A> it. Such a <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> is sometimes called a ``global variable'' but is still in all respects just a <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> whose <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> happens to exist in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A> rather than in some <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_environment"><I>dynamic environment</I></A>. <P>
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A <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_variable"><I>dynamic variable</I></A> is <A REL=DEFINITION HREF="26_glo_u.htm#unbound"><I>unbound</I></A> unless and until explicitly assigned a value, except for those variables whose initial value is defined in this specification or by an <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A>. <P>
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