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<!DOCTYPE HTML>
<HTML LANG="en-us"
><HEAD
><TITLE
>print-object | Common Lisp Nova Spec</TITLE
><META CHARSET="US-ASCII"
><LINK REL="canonical" HREF="f_print-object.html"
><LINK REL="next" HREF="f_print-unreadable-object.html" TYPE="text/html" TITLE="print-unreadable-object"
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><LINK REL="up" HREF="22_4_Printer_Dictionary.html" TYPE="text/html" TITLE="22.4 Printer Dictionary"
><LINK REL="start" HREF="index.html" TYPE="text/html" TITLE="Common Lisp Nova Spec"
><META NAME="VIEWPORT" CONTENT="width=device-width, initial-scale=1.0"
><LINK REL="STYLESHEET" HREF="dpans.css%3F3909942064.css"
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></SCRIPT
></HEAD
><BODY
><DIV
><DIV CLASS="topnav"
><DIV CLASS="breadcrumb"
><SPAN CLASS="breadcrumb-item"
><A HREF="index.html"
>Common Lisp Nova Spec</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="22_Printer.html"
>22. Printer</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="22_4_Printer_Dictionary.html"
>22.4 Printer Dictionary</A
></SPAN
> <SPAN CLASS="breadcrumb-item"
>&#8594; <A HREF="f_print-object.html"
>print-object</A
></SPAN
></DIV
><DIV CLASS="apropos"
><DIV CLASS="apropos-io"
><A HREF="f_pprint-tab.html" CLASS="prev"
>&#8592;</A
><SPAN ID="apropos-label"
>Apropos </SPAN
><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
><A HREF="f_print-unreadable-object.html" CLASS="next"
>&#8594;</A
></DIV
><DIV ID="apropos-res"
></DIV
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></DIV
><DIV CLASS="matter"
><DIV CLASS="com"
><DIV CLASS="begincom"
><HR
><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
><TR
><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="print-object"
></SPAN
><B
>print-object</B
></TD
><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
><I
>Standard</I
> <I
>Generic</I
> <I
>Function</I
></TD
></TR
></TABLE
><HR
></DIV
><UL CLASS="subtoc"
></UL
><DL
><DT
><B
>Syntax</B
></DT
><DD
><P CLASS="j"
><B
>print-object</B
> <SPAN CLASS="cmssi"
>object</SPAN
> <SPAN CLASS="cmssi"
>stream</SPAN
> <SPAN CLASS="arrow"
>&#8594;</SPAN
> <SPAN CLASS="cmssi"
>object</SPAN
></P
></DD
><DT
><B
>Method Signatures</B
></DT
><DD
><P CLASS="j"
><B
>print-object</B
> (<VAR CLASS="param"
>object</VAR
> <SPAN CLASS="cmssi"
>standard-object</SPAN
>) <VAR CLASS="param"
>stream</VAR
></P
><P CLASS="j"
><B
>print-object</B
> (<VAR CLASS="param"
>object</VAR
> <SPAN CLASS="cmssi"
>structure-object</SPAN
>) <VAR CLASS="param"
>stream</VAR
></P
></DD
><DT
><B
>Arguments and Values</B
></DT
><DD
><P CLASS="j"
><VAR CLASS="param"
>object</VAR
> &#8212; an <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>object</EM
></A
>. </P
><P CLASS="j"
><VAR CLASS="param"
>stream</VAR
> &#8212; a <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
>.</P
></DD
><DT
><B
>Description</B
></DT
><DD
><P CLASS="j"
>The <A HREF="26_1_Glossary.html#generic_function"
><EM CLASS="term"
>generic function</EM
></A
> <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> writes the printed representation of <VAR CLASS="param"
>object</VAR
> to <VAR CLASS="param"
>stream</VAR
>. The <A HREF="26_1_Glossary.html#function"
><EM CLASS="term"
>function</EM
></A
> <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> is called by the <A HREF="26_1_Glossary.html#Lisp_printer"
><EM CLASS="term"
>Lisp printer</EM
></A
>; it should not be called by the user. </P
><P CLASS="j"
>Each implementation is required to provide a <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> on the <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>class</EM
></A
> <A HREF="t_standard-object.html" CLASS="typeref"
><B
>standard-object</B
></A
> and on the <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>class</EM
></A
> <A HREF="t_structure-object.html" CLASS="typeref"
><B
>structure-object</B
></A
>. In addition, each <A HREF="26_1_Glossary.html#implementation"
><EM CLASS="term"
>implementation</EM
></A
> must provide <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> on enough other <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>classes</EM
></A
> so as to ensure that there is always an applicable <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
>. Implementations are free to add <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> for other <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>classes</EM
></A
>. Users may write <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> for <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> for their own <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>classes</EM
></A
> if they do not wish to inherit an <A HREF="26_1_Glossary.html#implementation-dependent"
><EM CLASS="term"
>implementation-dependent</EM
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
>. </P
><P CLASS="j"
>The <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> on the <A HREF="26_1_Glossary.html#class"
><EM CLASS="term"
>class</EM
></A
> <A HREF="t_structure-object.html" CLASS="typeref"
><B
>structure-object</B
></A
> prints the object in the default <CODE CLASS="f"
>#S</CODE
> notation; see <A HREF="22_1_The_Lisp_Printer.html#sec_22_1_3_12" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.1.3.12</SPAN
> <SPAN CLASS="cmr"
>(Printing</SPAN
> <SPAN CLASS="cmr"
>Structures)</SPAN
></A
>. </P
><P CLASS="j"
><A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>Methods</EM
></A
> on <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> are responsible for implementing their part of the semantics of the <A HREF="26_1_Glossary.html#printer_control_variable"
><EM CLASS="term"
>printer control variables</EM
></A
>, as follows:</P
><DL
><DT
><SPAN CLASS="item"
><A HREF="v_print-readably.html" CLASS="varref"
><B
>*print-readably*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>All methods for <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> must obey <A HREF="v_print-readably.html" CLASS="varref"
><B
>*print-readably*</B
></A
>. This includes both user-defined methods and <A HREF="26_1_Glossary.html#implementation-defined"
><EM CLASS="term"
>implementation-defined</EM
></A
> methods. Readable printing of <A HREF="26_1_Glossary.html#structure"
><EM CLASS="term"
>structures</EM
></A
> and <A HREF="26_1_Glossary.html#standard_object"
><EM CLASS="term"
>standard objects</EM
></A
> is controlled by their <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> method, not by their <A HREF="f_make-load-form.html" CLASS="funref"
><B
>make-load-form</B
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
>. <A HREF="26_1_Glossary.html#similarity"
><EM CLASS="term"
>Similarity</EM
></A
> for these <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>objects</EM
></A
> is application dependent and hence is defined to be whatever these <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> do; see <A HREF="3_2_Compilation.html#sec_3_2_4_2" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>3.2.4.2</SPAN
> <SPAN CLASS="cmr"
>(Similarity</SPAN
> <SPAN CLASS="cmr"
>of</SPAN
> <SPAN CLASS="cmr"
>Literal</SPAN
> <SPAN CLASS="cmr"
>Objects)</SPAN
></A
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-escape.html" CLASS="varref"
><B
>*print-escape*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>Each <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> must implement <A HREF="v_print-escape.html" CLASS="varref"
><B
>*print-escape*</B
></A
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-pretty.html" CLASS="varref"
><B
>*print-pretty*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>The <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> may wish to perform specialized line breaking or other output conditional on the <A HREF="26_1_Glossary.html#value"
><EM CLASS="term"
>value</EM
></A
> of <A HREF="v_print-pretty.html" CLASS="misc"
><B
>*print-pretty*</B
></A
>. For further information, see (for example) the <A HREF="26_1_Glossary.html#macro"
><EM CLASS="term"
>macro</EM
></A
> <A HREF="f_pprint-fill.html" CLASS="funref"
><B
>pprint-fill</B
></A
>. See also <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_1_4" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.1.4</SPAN
> <SPAN CLASS="cmr"
>(Pretty</SPAN
> <SPAN CLASS="cmr"
>Print</SPAN
> <SPAN CLASS="cmr"
>Dispatch</SPAN
> <SPAN CLASS="cmr"
>Tables)</SPAN
></A
> and <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_2" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.2</SPAN
> <SPAN CLASS="cmr"
>(Examples</SPAN
> <SPAN CLASS="cmr"
>of</SPAN
> <SPAN CLASS="cmr"
>using</SPAN
> <SPAN CLASS="cmr"
>the</SPAN
> <SPAN CLASS="cmr"
>Pretty</SPAN
> <SPAN CLASS="cmr"
>Printer)</SPAN
></A
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-level.html" CLASS="varref"
><B
>*print-length*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
><A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>Methods</EM
></A
> that produce output of indefinite length must obey <A HREF="v_print-level.html" CLASS="varref"
><B
>*print-length*</B
></A
>. For further information, see (for example) the <A HREF="26_1_Glossary.html#macro"
><EM CLASS="term"
>macros</EM
></A
> <A HREF="f_pprint-logical-block.html" CLASS="macref"
><B
>pprint-logical-block</B
></A
> and <A HREF="f_pprint-pop.html" CLASS="macref"
><B
>pprint-pop</B
></A
>. See also <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_1_4" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.1.4</SPAN
> <SPAN CLASS="cmr"
>(Pretty</SPAN
> <SPAN CLASS="cmr"
>Print</SPAN
> <SPAN CLASS="cmr"
>Dispatch</SPAN
> <SPAN CLASS="cmr"
>Tables)</SPAN
></A
> and <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_2" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.2</SPAN
> <SPAN CLASS="cmr"
>(Examples</SPAN
> <SPAN CLASS="cmr"
>of</SPAN
> <SPAN CLASS="cmr"
>using</SPAN
> <SPAN CLASS="cmr"
>the</SPAN
> <SPAN CLASS="cmr"
>Pretty</SPAN
> <SPAN CLASS="cmr"
>Printer)</SPAN
></A
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-level.html" CLASS="varref"
><B
>*print-level*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>The printer takes care of <A HREF="v_print-level.html" CLASS="varref"
><B
>*print-level*</B
></A
> automatically, provided that each <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> handles exactly one level of structure and calls <A HREF="f_write.html" CLASS="funref"
><B
>write</B
></A
> (or an equivalent <A HREF="26_1_Glossary.html#function"
><EM CLASS="term"
>function</EM
></A
>) recursively if there are more structural levels. The printer&#8217;s decision of whether an <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>object</EM
></A
> has components (and therefore should not be printed when the printing depth is not less than <A HREF="v_print-level.html" CLASS="varref"
><B
>*print-level*</B
></A
>) is <A HREF="26_1_Glossary.html#implementation-dependent"
><EM CLASS="term"
>implementation-dependent</EM
></A
>. In some implementations its <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> is not called; in others the <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> is called, and the determination that the <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>object</EM
></A
> has components is based on what it tries to write to the <VAR CLASS="param"
>stream</VAR
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-circle.html" CLASS="varref"
><B
>*print-circle*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>When the <A HREF="26_1_Glossary.html#value"
><EM CLASS="term"
>value</EM
></A
> of <A HREF="v_print-circle.html" CLASS="misc"
><B
>*print-circle*</B
></A
> is <A HREF="26_1_Glossary.html#true"
><EM CLASS="term"
>true</EM
></A
>, a user-defined <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> can print <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>objects</EM
></A
> to the supplied <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
> using <A HREF="f_write.html" CLASS="funref"
><B
>write</B
></A
>, <A HREF="f_write.html" CLASS="funref"
><B
>prin1</B
></A
>, <A HREF="f_write.html" CLASS="funref"
><B
>princ</B
></A
>, or <A HREF="f_format.html" CLASS="funref"
><B
>format</B
></A
> and expect circularities to be detected and printed using the <CODE CLASS="f"
>#<I CLASS="i"
><I
>n</I
></I
>#</CODE
> syntax. If a user-defined <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> prints to a <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
> other than the one that was supplied, then circularity detection starts over for that <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
>. See <A HREF="v_print-circle.html" CLASS="varref"
><B
>*print-circle*</B
></A
>.</P
></DD
><DT
><SPAN CLASS="item"
><A HREF="v_print-base.html" CLASS="varref"
><B
>*print-base*</B
></A
><SPAN CLASS="cmr"
>,</SPAN
> <A HREF="v_print-base.html" CLASS="varref"
><B
>*print-radix*</B
></A
><SPAN CLASS="cmr"
>,</SPAN
> <A HREF="v_print-case.html" CLASS="varref"
><B
>*print-case*</B
></A
><SPAN CLASS="cmr"
>,</SPAN
> <A HREF="v_print-gensym.html" CLASS="varref"
><B
>*print-gensym*</B
></A
><SPAN CLASS="cmr"
>,</SPAN
> <SPAN CLASS="cmr"
>and</SPAN
> <A HREF="v_print-array.html" CLASS="varref"
><B
>*print-array*</B
></A
></SPAN
></DT
><DD
><P CLASS="j"
>These <A HREF="26_1_Glossary.html#printer_control_variable"
><EM CLASS="term"
>printer control variables</EM
></A
> apply to specific types of <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>objects</EM
></A
> and are handled by the <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> for those <A HREF="26_1_Glossary.html#object"
><EM CLASS="term"
>objects</EM
></A
>.</P
></DD
></DL
><P CLASS="j"
>If these rules are not obeyed, the results are undefined. </P
><P CLASS="j"
>In general, the printer and the <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> methods should not rebind the print control variables as they operate recursively through the structure, but this is <A HREF="26_1_Glossary.html#implementation-dependent"
><EM CLASS="term"
>implementation-dependent</EM
></A
>. </P
><P CLASS="j"
>In some implementations the <VAR CLASS="param"
>stream</VAR
> argument passed to a <A HREF="f_print-object.html" CLASS="funref"
><B
>print-object</B
></A
> <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>method</EM
></A
> is not the original <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
>, but is an intermediate <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
> that implements part of the printer. <A HREF="26_1_Glossary.html#method"
><EM CLASS="term"
>methods</EM
></A
> should therefore not depend on the identity of this <A HREF="26_1_Glossary.html#stream"
><EM CLASS="term"
>stream</EM
></A
>.</P
></DD
><DT
><B
>See Also</B
></DT
><DD
><P CLASS="j"
><A HREF="f_pprint-fill.html" CLASS="funref"
><B
>pprint-fill</B
></A
>, <A HREF="f_pprint-logical-block.html" CLASS="macref"
><B
>pprint-logical-block</B
></A
>, <A HREF="f_pprint-pop.html" CLASS="macref"
><B
>pprint-pop</B
></A
>, <A HREF="f_write.html" CLASS="funref"
><B
>write</B
></A
>, <A HREF="v_print-readably.html" CLASS="varref"
><B
>*print-readably*</B
></A
>, <A HREF="v_print-escape.html" CLASS="varref"
><B
>*print-escape*</B
></A
>, <A HREF="v_print-pretty.html" CLASS="varref"
><B
>*print-pretty*</B
></A
>, <A HREF="v_print-level.html" CLASS="varref"
><B
>*print-length*</B
></A
>, <A HREF="22_1_The_Lisp_Printer.html#sec_22_1_3" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.1.3</SPAN
> <SPAN CLASS="cmr"
>(Default</SPAN
> <SPAN CLASS="cmr"
>Print-Object</SPAN
> <SPAN CLASS="cmr"
>Methods)</SPAN
></A
>, <A HREF="22_1_The_Lisp_Printer.html#sec_22_1_3_12" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.1.3.12</SPAN
> <SPAN CLASS="cmr"
>(Printing</SPAN
> <SPAN CLASS="cmr"
>Structures)</SPAN
></A
>, <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_1_4" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.1.4</SPAN
> <SPAN CLASS="cmr"
>(Pretty</SPAN
> <SPAN CLASS="cmr"
>Print</SPAN
> <SPAN CLASS="cmr"
>Dispatch</SPAN
> <SPAN CLASS="cmr"
>Tables)</SPAN
></A
>, <A HREF="22_2_The_Lisp_Pretty_Printer.html#sec_22_2_2" CLASS="secref"
><SPAN CLASS="cmr"
>Section</SPAN
> <SPAN CLASS="cmr"
>22.2.2</SPAN
> <SPAN CLASS="cmr"
>(Examples</SPAN
> <SPAN CLASS="cmr"
>of</SPAN
> <SPAN CLASS="cmr"
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