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<h5 class="subsubsection">2.5.1.2 Standard Output Representation</h5>

<p><a name="index-standard-output-187"></a><a name="index-g_t_0040code_007braw_002doutput_007d-command-line-option-188"></a><a name="index-g_t_0040code_007bchoice_002dof_002doutput_007d-command-line-option-189"></a>As in the case of standard input, the representation for standard output
that the function is expected to return depends on the command line
options with which the application is invoked. The only relevant options
are <samp><span class="option">--raw-output</span></samp> and <samp><span class="option">--choice-of-output</span></samp>, which are
mutually exclusive.

     <ul>
<li>If neither option is selected, the result returned by the function must
be a list of character strings. 
<li>If <samp><span class="option">--raw-output</span></samp> is used, the result returned by the
function is unconstrained, and it will be written as a data file with no
preamble, following the format specified in <a href="File-Format.html#File-Format">File Format</a>. 
<li>If <samp><span class="option">--choice-of-output</span></samp> is used, the result returned by the
function must be a pair <code>(</code><var>preamble</var><code>,</code><var>contents</var><code>)</code>. 
</ul>

   <p><a name="index-preamble-190"></a>In the last case, the preamble determines how the file will be written. 
If it is meant to be a text file, the preamble should be <code>nil</code>, and
the contents should be a list of character strings. If it is meant to be
a data file, the preamble should be a non-empty list of character
strings, and the format of the contents is unconstrained. To express a
data file with no preamble, the preamble should be the list containing
the empty string, rather than being empty.

   <p>In the result returned by the function, the preamble lines should not
include leading hash characters, because they are automatically added to
the output to enforce consistency with the data file format. However,
they should include trailing backslashes as continuation characters
where appropriate. The hashes that are automatically added will be
automatically stripped by <code>avram</code> on behalf of whatever application
uses the file.

   <p><a name="index-character-strings-191"></a><a name="index-printing-algorithm-192"></a>Any file can be written as a list of character strings, even &ldquo;text&rdquo;
files that are full of unprintable characters, and even &ldquo;text&rdquo; files
that happen to conform to the format used for data files.  However, if
the application intends to write a data file in the standard format used
by other virtual code applications, it can do so more quickly and easily
by having the virtual machine do the formatting automatically with the
<samp><span class="option">--choice-of-output</span></samp> option than by implementing the algorithm in
<a href="Concrete-Syntax.html#Concrete-Syntax">Concrete Syntax</a>, from scratch in virtual code.

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