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65 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: Local Macro PPRINT-POP</TITLE>
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<A NAME="pprint-pop"><I>Local Macro</I> <B>PPRINT-POP</B></A> <P>
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<P>
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<P><B>Syntax:</B><P>
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<P>
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<B>pprint-pop</B> <I><I><no arguments></I></I> => <I>object</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>object</I>---an <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A> of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> being printed in the <I>lexically current logical block</I>, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<P><B>Description:</B><P>
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<P>
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Pops one <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A> from the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> being printed in the <I>lexically current logical block</I>, obeying <A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A> and <A REL=DEFINITION HREF="v_pr_cir.htm#STprint-circleST"><B>*print-circle*</B></A> as described below. <P>
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Each time <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> is called, it pops the next value off the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> passed to the <I>lexically current logical block</I> and returns it. However, before doing this, it performs three tests: <P>
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<P><UL><LI> If the remaining `list' is not a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, ``<TT>. </TT>'' is printed followed by the remaining `list.' (This makes it easier to write printing functions that are robust in the face of malformed arguments.) <P>
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<LI> If <A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A> is <A REL=DEFINITION HREF="26_glo_n.htm#non-nil"><I>non-nil</I></A>, and <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> has already been called <A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A> times within the immediately containing logical block, ``<TT>...</TT>'' is printed. (This makes it easy to write printing functions that properly handle <A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A>.) <P>
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<LI> If <A REL=DEFINITION HREF="v_pr_cir.htm#STprint-circleST"><B>*print-circle*</B></A> is <A REL=DEFINITION HREF="26_glo_n.htm#non-nil"><I>non-nil</I></A>, and the remaining list is a circular (or shared) reference, then ``<TT>. </TT>'' is printed followed by an appropriate ``<TT>#</TT><I>n</I><TT>#</TT>'' marker. (This catches instances of <A REL=DEFINITION HREF="26_glo_c.htm#cdr"><I>cdr</I></A> circularity and sharing in lists.) <P></UL><P>
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If either of the three conditions above occurs, the indicated output is printed on the <A REL=DEFINITION HREF="26_glo_p.htm#pretty_printing_stream"><I>pretty printing stream</I></A> created by the immediately containing <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A> and the execution of the immediately containing <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A> is terminated except for the printing of the suffix. <P>
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If <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A> is given a `list' argument of <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>---because it is not processing a list---<A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> can still be used to obtain support for <A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A>. In this situation, the first and third tests above are disabled and <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> always returns <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. See <A REL=CHILD HREF="22_bb.htm">Section 22.2.2 (Examples of using the Pretty Printer)</A>---specifically, the <B>pprint-vector</B> example. <P>
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Whether or not <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> is <A REL=DEFINITION HREF="26_glo_f.htm#fbound"><I>fbound</I></A> in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A> is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A>; however, the restrictions on redefinition and <I>shadowing</I> of <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> are the same as for <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A> in the <TT>COMMON-LISP</TT> package which are <A REL=DEFINITION HREF="26_glo_f.htm#fbound"><I>fbound</I></A> in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A>. The consequences of attempting to use <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> outside of <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A> are undefined. <P>
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<P><B>Examples:</B> None.
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<P>
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<P><B>Side Effects:</B><P>
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<P>
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Might cause output to the <A REL=DEFINITION HREF="26_glo_p.htm#pretty_printing_stream"><I>pretty printing stream</I></A> associated with the lexically current logical block. <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="v_pr_lev.htm#STprint-lengthST"><B>*print-length*</B></A>, <A REL=DEFINITION HREF="v_pr_cir.htm#STprint-circleST"><B>*print-circle*</B></A>. <P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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An error is signaled (either at macro expansion time or at run time) if a usage of <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> occurs where there is no lexically containing <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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The consequences are undefined if <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A> is executed outside of the <A REL=DEFINITION HREF="26_glo_d.htm#dynamic_extent"><I>dynamic extent</I></A> of this <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A>. <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_ppr_ex.htm#pprint-exit-if-list-exhausted"><B>pprint-exit-if-list-exhausted</B></A>, <A REL=DEFINITION HREF="m_ppr_lo.htm#pprint-logical-block"><B>pprint-logical-block</B></A>. <P>
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<P><B>Notes:</B><P>
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<P>
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It is frequently a good idea to call <A REL=DEFINITION HREF="m_ppr_ex.htm#pprint-exit-if-list-exhausted"><B>pprint-exit-if-list-exhausted</B></A> before calling <A REL=DEFINITION HREF="#pprint-pop"><B>pprint-pop</B></A>. <P>
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss211.htm">LEXICAL-CONSTRUCT-GLOBAL-DEFINITION:UNDEFINED</A><LI> <A REL=CHILD HREF="../Issues/iss270.htm">PRETTY-PRINT-INTERFACE</A><P></UL><HR>
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