88 lines
9.1 KiB
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88 lines
9.1 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: Function READ-DELIMITED-LIST</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="f_rd_rd.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_reader.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_rd_fro.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="read-delimited-list"><I>Function</I> <B>READ-DELIMITED-LIST</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>read-delimited-list</B> <I>char <TT>&optional</TT> input-stream recursive-p</I> => <I>list</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>char</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A>. <P>
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<I>input-stream</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#input"><I>input</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#stream_designator"><I>stream designator</I></A>. The default is <A REL=DEFINITION HREF="26_glo_s.htm#standard_input"><I>standard input</I></A>. <P>
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<I>recursive-p</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. The default is <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A>. <P>
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<I>list</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of the <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> read. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> reads <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> from <I>input-stream</I> until the next character after an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>'s representation (ignoring <A REL=DEFINITION HREF="26_glo_w.htm#whitespace"><I>whitespace</I></A>[2] characters and comments) is <I>char</I>. <P>
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<A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> looks ahead at each step for the next non-<A REL=DEFINITION HREF="26_glo_w.htm#whitespace"><I>whitespace</I></A>[2] <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A> and peeks at it as if with <A REL=DEFINITION HREF="f_peek_c.htm#peek-char"><B>peek-char</B></A>. If it is <I>char</I>, then the <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A> is consumed and the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>objects</I></A> is returned. If it is a <A REL=DEFINITION HREF="26_glo_c.htm#constituent"><I>constituent</I></A> or <A REL=DEFINITION HREF="26_glo_e.htm#escape"><I>escape</I></A> <A REL=DEFINITION HREF="26_glo_c.htm#character"><I>character</I></A>, then <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> is used to read an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>, which is added to the end of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. If it is a <A REL=DEFINITION HREF="26_glo_m.htm#macro_character"><I>macro character</I></A>, its <A REL=DEFINITION HREF="26_glo_r.htm#reader_macro_function"><I>reader macro function</I></A> is called; if the function returns a <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A>, that <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> is added to the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. The peek-ahead process is then repeated. <P>
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If <I>recursive-p</I> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, this call is expected to be embedded in a higher-level call to <A REL=DEFINITION HREF="f_rd_rd.htm#read"><B>read</B></A> or a similar function. <P>
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It is an error to reach end-of-file during the operation of <A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A>. <P>
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The consequences are undefined if <I>char</I> has a <A REL=DEFINITION HREF="26_glo_s.htm#syntax_type"><I>syntax type</I></A> of <A REL=DEFINITION HREF="26_glo_w.htm#whitespace"><I>whitespace</I></A>[2] in the <A REL=DEFINITION HREF="26_glo_c.htm#current_readtable"><I>current readtable</I></A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(read-delimited-list #\]) 1 2 3 4 5 6 ]
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=> (1 2 3 4 5 6)
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</PRE>
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</TT> Suppose you wanted <TT>#{</TT><I>a</I><TT> </TT><I>b</I><TT> </TT><I>c</I><TT> ... </TT><I>z</I><TT>}</TT> to read as a list of all pairs of the elements <I>a</I>, <I>b</I>, <I>c</I>, ..., <I>z</I>, for example. <P>
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<PRE>
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#{p q z a} reads as ((p q) (p z) (p a) (q z) (q a) (z a))
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</PRE>
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</TT> This can be done by specifying a macro-character definition for <TT>#{</TT> that does two things: reads in all the items up to the <TT>}</TT>, and constructs the pairs. <A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> performs the first task. <P>
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<PRE>
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(defun |#{-reader| (stream char arg)
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(declare (ignore char arg))
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(mapcon #'(lambda (x)
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(mapcar #'(lambda (y) (list (car x) y)) (cdr x)))
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(read-delimited-list #\} stream t))) => |#{-reader|
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(set-dispatch-macro-character #\# #\{ #'|#{-reader|) => T
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(set-macro-character #\} (get-macro-character #\) <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>))
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</PRE>
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</TT> Note that <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> is supplied for the <I>recursive-p</I> argument. <P>
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It is necessary here to give a definition to the character <TT>}</TT> as well to prevent it from being a constituent. If the line <P>
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<PRE>
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(set-macro-character #\} (get-macro-character #\) <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>))
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</PRE>
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</TT> shown above were not included, then the <TT>}</TT> in <P>
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<PRE>
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#{ p q z a}
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</PRE>
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</TT> would be considered a constituent character, part of the symbol named <TT>a}</TT>. This could be corrected by putting a space before the <TT>}</TT>, but it is better to call <A REL=DEFINITION HREF="f_set_ma.htm#set-macro-character"><B>set-macro-character</B></A>. <P>
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Giving <TT>}</TT> the same definition as the standard definition of the character <TT>)</TT> has the twin benefit of making it terminate tokens for use with <A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> and also making it invalid for use in any other context. Attempting to read a stray <TT>}</TT> will signal an error. <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_debug_.htm#STstandard-inputST"><B>*standard-input*</B></A>, <A REL=DEFINITION HREF="v_rdtabl.htm#STreadtableST"><B>*readtable*</B></A>, <A REL=DEFINITION HREF="v_termin.htm#STterminal-ioST"><B>*terminal-io*</B></A>. <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="f_rd_rd.htm#read"><B>read</B></A>, <A REL=DEFINITION HREF="f_peek_c.htm#peek-char"><B>peek-char</B></A>, <A REL=DEFINITION HREF="f_rd_cha.htm#read-char"><B>read-char</B></A>, <A REL=DEFINITION HREF="f_unrd_c.htm#unread-char"><B>unread-char</B></A>. <P>
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<P><B>Notes:</B><P>
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<P>
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<A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> is intended for use in implementing <A REL=DEFINITION HREF="26_glo_r.htm#reader_macro"><I>reader macros</I></A>. Usually it is desirable for <I>char</I> to be a <A REL=DEFINITION HREF="26_glo_t.htm#terminating"><I>terminating</I></A> <A REL=DEFINITION HREF="26_glo_m.htm#macro_character"><I>macro character</I></A> so that it can be used to delimit tokens; however, <A REL=DEFINITION HREF="#read-delimited-list"><B>read-delimited-list</B></A> makes no attempt to alter the syntax specified for <I>char</I> by the current readtable. The caller must make any necessary changes to the readtable syntax explicitly. <P>
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