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60 lines
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<TITLE>CLHS: Section 24.1.2.1.1</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="24_aba.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="24_aba.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="c_system.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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24.1.2.1.1 Examples of Feature Expressions</H2> For example, suppose that in <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> A, the <A REL=DEFINITION HREF="26_glo_f.htm#feature"><I>features</I></A> <TT>spice</TT> and <TT>perq</TT> are <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A>, but the <A REL=DEFINITION HREF="26_glo_f.htm#feature"><I>feature</I></A> <TT>lispm</TT> is not <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A>; in <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> B, the feature <TT>lispm</TT> is <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A>, but the <A REL=DEFINITION HREF="26_glo_f.htm#feature"><I>features</I></A> <TT>spice</TT> and <TT>perq</TT> are not <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A>; and in <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> C, none of the features <TT>spice</TT>, <I>lispm</I>, or <TT>perq</TT> are <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A>. The next figure shows some sample <A REL=DEFINITION HREF="26_glo_e.htm#expression"><I>expressions</I></A>, and how they would be <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A>[2] in these <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>. <P>
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<PRE>
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(cons #+spice "Spice" #-spice "Lispm" x)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> A ... (CONS "Spice" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> B ... (CONS "Lispm" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> C ... (CONS "Lispm" X)
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(cons #+spice "Spice" #+LispM "Lispm" x)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> A ... (CONS "Spice" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> B ... (CONS "Lispm" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> C ... (CONS X)
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(setq a '(1 2 #+perq 43 #+(not perq) 27))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> A ... (SETQ A '(1 2 43))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> B ... (SETQ A '(1 2 27))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> C ... (SETQ A '(1 2 27))
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(let ((a 3) #+(or spice lispm) (b 3)) (foo a))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> A ... (LET ((A 3) (B 3)) (FOO A))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> B ... (LET ((A 3) (B 3)) (FOO A))
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> C ... (LET ((A 3)) (FOO A))
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(cons #+Lispm "#+Spice" #+Spice "foo" #-(or Lispm Spice) 7 x)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> A ... (CONS "foo" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> B ... (CONS "#+Spice" X)
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in <A REL=DEFINITION HREF="26_glo_i.htm#implementation">implementation</A> C ... (CONS 7 X)
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</PRE>
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<P><B>Figure 24-1. Features examples</B> <HR>
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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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