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>with-output-to-string | Common Lisp Nova Spec</TITLE
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>Common Lisp Nova Spec</A
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="with-output-to-string"
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></SPAN
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><B
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>with-output-to-string</B
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Macro</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Syntax</B
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></DT
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><DD
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><DIV CLASS="DefmacWithValuesNewline"
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><DIV
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><B
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>with-output-to-string</B
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> <SPAN CLASS="cmr"
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>(</SPAN
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><SPAN CLASS="cmssi"
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>var</SPAN
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> <SPAN CLASS="cmtt"
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>&optional</SPAN
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> <SPAN CLASS="cmssi"
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>string-form</SPAN
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> <SPAN CLASS="cmtt"
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>&key</SPAN
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> <SPAN CLASS="cmssi"
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>element-type</SPAN
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><SPAN CLASS="cmr"
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>)</SPAN
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> <SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>declaration</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*</SPAN
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> <SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>form</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*</SPAN
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> </DIV
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><DIV
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><SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> <SPAN CLASS="cmsy"
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>{</SPAN
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><VAR CLASS="param"
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>result</VAR
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><SPAN CLASS="cmsy"
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>}</SPAN
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><SPAN CLASS="cmr"
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>*</SPAN
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></DIV
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></DIV
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></DD
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><DT
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><B
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>Arguments and Values</B
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></DT
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><DD
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><P CLASS="j"
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><VAR CLASS="param"
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>var</VAR
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> — a <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> <A HREF="26_1_Glossary.html#name"
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><EM CLASS="term"
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>name</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>string-form</VAR
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> — a <A HREF="26_1_Glossary.html#form"
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><EM CLASS="term"
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>form</EM
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></A
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> or <SPAN CLASS="misc"
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><B
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>nil</B
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></SPAN
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>; if <A HREF="26_1_Glossary.html#non-nil"
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><EM CLASS="term"
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>non-nil</EM
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></A
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>, evaluated to produce <VAR CLASS="param"
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>string</VAR
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>string</VAR
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> — a <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>string</EM
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></A
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> that has a <A HREF="26_1_Glossary.html#fill_pointer"
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><EM CLASS="term"
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>fill pointer</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>element-type</VAR
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> — a <A HREF="26_1_Glossary.html#type_specifier"
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><EM CLASS="term"
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>type specifier</EM
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></A
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>; evaluated. The default is <A HREF="t_character.html" CLASS="typeref"
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><B
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>character</B
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>declaration</VAR
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> — a <A HREF="m_declare.html" CLASS="misc"
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><B
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>declare</B
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></A
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> <A HREF="26_1_Glossary.html#expression"
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><EM CLASS="term"
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>expression</EM
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></A
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>; not evaluated. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>forms</VAR
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> — an <A HREF="26_1_Glossary.html#implicit_progn"
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><EM CLASS="term"
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>implicit progn</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>results</VAR
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> — If a <VAR CLASS="param"
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>string-form</VAR
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> is not supplied or <SPAN CLASS="misc"
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><B
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>nil</B
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></SPAN
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>, a <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>string</EM
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></A
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>; otherwise, the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>values</EM
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></A
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> returned by the <VAR CLASS="param"
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>forms</VAR
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="f_with-output-to-string.html" CLASS="macref"
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><B
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>with-output-to-string</B
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></A
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> creates a character <A HREF="26_1_Glossary.html#output"
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><EM CLASS="term"
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>output</EM
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></A
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> <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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>, performs a series of operations that may send results to this <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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>, and then closes the <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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>. </P
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><P CLASS="j"
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>The <VAR CLASS="param"
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>element-type</VAR
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> names the <A HREF="26_1_Glossary.html#type"
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><EM CLASS="term"
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>type</EM
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></A
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> of the elements of the <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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>; a <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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> is constructed of the most specialized <A HREF="26_1_Glossary.html#type"
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><EM CLASS="term"
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>type</EM
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></A
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> that can accommodate elements of the given <A HREF="26_1_Glossary.html#type"
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><EM CLASS="term"
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>type</EM
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></A
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>. </P
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><P CLASS="j"
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>The body is executed as an <A HREF="26_1_Glossary.html#implicit_progn"
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><EM CLASS="term"
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>implicit progn</EM
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></A
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> with <VAR CLASS="param"
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>var</VAR
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> bound to an <A HREF="26_1_Glossary.html#output"
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><EM CLASS="term"
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>output</EM
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></A
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> <A HREF="26_1_Glossary.html#string_stream"
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><EM CLASS="term"
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>string stream</EM
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></A
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>. All output to that <A HREF="26_1_Glossary.html#string_stream"
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><EM CLASS="term"
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>string stream</EM
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></A
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> is saved in a <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>string</EM
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></A
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>. </P
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><P CLASS="j"
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>If <VAR CLASS="param"
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>string</VAR
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> is supplied, <VAR CLASS="param"
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>element-type</VAR
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> is ignored, and the output is incrementally appended to <VAR CLASS="param"
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>string</VAR
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> as if by use of <A HREF="f_vector-push.html" CLASS="funref"
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><B
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>vector-push-extend</B
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></A
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>. </P
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><P CLASS="j"
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>The <A HREF="26_1_Glossary.html#output"
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><EM CLASS="term"
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>output</EM
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></A
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> <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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> is automatically closed on exit from <A HREF="f_with-output-to-string.html" CLASS="macref"
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><B
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>with-output-to-string</B
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></A
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>, no matter whether the exit is normal or abnormal. The <A HREF="26_1_Glossary.html#output"
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><EM CLASS="term"
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>output</EM
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></A
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> <A HREF="26_1_Glossary.html#string_stream"
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><EM CLASS="term"
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>string stream</EM
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></A
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> to which the <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> <VAR CLASS="param"
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>var</VAR
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> is <A HREF="26_1_Glossary.html#bound"
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><EM CLASS="term"
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>bound</EM
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></A
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> has <A HREF="26_1_Glossary.html#dynamic_extent"
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><EM CLASS="term"
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>dynamic extent</EM
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></A
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>; its <A HREF="26_1_Glossary.html#extent"
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><EM CLASS="term"
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>extent</EM
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></A
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> ends when the <A HREF="26_1_Glossary.html#form"
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><EM CLASS="term"
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>form</EM
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></A
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> is exited. </P
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><P CLASS="j"
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>If no <VAR CLASS="param"
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>string</VAR
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> is provided, then <A HREF="f_with-output-to-string.html" CLASS="macref"
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><B
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>with-output-to-string</B
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></A
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> produces a <A HREF="26_1_Glossary.html#stream"
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><EM CLASS="term"
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>stream</EM
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></A
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> that accepts characters and returns a <A HREF="26_1_Glossary.html#string"
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><EM CLASS="term"
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>string</EM
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></A
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> of the indicated <VAR CLASS="param"
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>element-type</VAR
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>. If <VAR CLASS="param"
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>string</VAR
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> is provided, <A HREF="f_with-output-to-string.html" CLASS="macref"
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><B
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>with-output-to-string</B
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></A
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> returns the results of evaluating the last <VAR CLASS="param"
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>form</VAR
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>. </P
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><P CLASS="j"
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>The consequences are undefined if an attempt is made to <A HREF="26_1_Glossary.html#assign"
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><EM CLASS="term"
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>assign</EM
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></A
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> the <A HREF="26_1_Glossary.html#variable"
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><EM CLASS="term"
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>variable</EM
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></A
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> <VAR CLASS="param"
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>var</VAR
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>.</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
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><DD
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><PRE CLASS="screen"
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>(setq fstr (make-array '(0) :element-type 'base-char
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:fill-pointer 0 :adjustable t)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> ""
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(with-output-to-string (s fstr)
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(format s "here's some output")
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(input-stream-p s)) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> <A HREF="26_1_Glossary.html#false"
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><EM CLASS="term"
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>false</EM
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></A
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>
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|
fstr <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> "here's some output"</PRE
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></DD
|
|
><DT
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><B
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|
>Side Effects</B
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></DT
|
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><DD
|
|
><P CLASS="j"
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>The <VAR CLASS="param"
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>string</VAR
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> is modified.</P
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></DD
|
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><DT
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|
><B
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|
>Exceptional Situations</B
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|
></DT
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|
><DD
|
|
><P CLASS="j"
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|
>The consequences are undefined if destructive modifications are performed directly on the <VAR CLASS="param"
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>string</VAR
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> during the <A HREF="26_1_Glossary.html#dynamic_extent"
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><EM CLASS="term"
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>dynamic extent</EM
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></A
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> of the call.</P
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></DD
|
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><DT
|
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><B
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|
>See Also</B
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></DT
|
|
><DD
|
|
><P CLASS="j"
|
|
><A HREF="f_make-string-output-stream.html" CLASS="funref"
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><B
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>make-string-output-stream</B
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></A
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>, <A HREF="f_vector-push.html" CLASS="funref"
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><B
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>vector-push-extend</B
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|
></A
|
|
>, <A HREF="3_6_Traversal_Rules_and_Side_Effects.html#sec_3_6" CLASS="secref"
|
|
><SPAN CLASS="cmr"
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|
>Section</SPAN
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> <SPAN CLASS="cmr"
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>3.6</SPAN
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> <SPAN CLASS="cmr"
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|
>(Traversal</SPAN
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|
> <SPAN CLASS="cmr"
|
|
>Rules</SPAN
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|
> <SPAN CLASS="cmr"
|
|
>and</SPAN
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> <SPAN CLASS="cmr"
|
|
>Side</SPAN
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> <SPAN CLASS="cmr"
|
|
>Effects)</SPAN
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></A
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></P
|
|
></DD
|
|
></DL
|
|
></DIV
|
|
></DIV
|
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><DIV CLASS="footer"
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><DIV CLASS="btmnav"
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><A HREF="f_with-input-from-string.html" CLASS="prev"
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>←</A
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>→</A
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><DIV CLASS="trail"
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>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
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