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<title>avram - a virtual machine code interpreter: 2.5.1.1 Standard Input Representation</title>

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<a name="Standard-Input-Representation"></a>
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<hr size="1">
<a name="Standard-Input-Representation-1"></a>
<h4 class="subsubsection">2.5.1.1 Standard Input Representation</h4>

<a name="index-standard-input-6"></a>
<p>The representation for the standard input file used as the argument to
the function depends both on the file format and on the command line
options specified when the application is invoked. The
<a name="index-unparameterized-command-line-option-1"></a>
<a name="index-raw_002dmode-command-line-option"></a>
&lsquo;<samp>--unparameterized</samp>&rsquo; and &lsquo;<samp>--raw-output</samp>&rsquo; options make no
difference to the input representation, and the &lsquo;<samp>--line-map</samp>&rsquo;
and &lsquo;<samp>--byte-transducer</samp>&rsquo; options are not relevant to this mode of
operation. That leaves four possible combined settings of the
<a name="index-choice_002dof_002doutput-command-line-option-1"></a>
<a name="index-force_002dtext_002dinput-command-line-option-1"></a>
&lsquo;<samp>--choice-of-output</samp>&rsquo; and &lsquo;<samp>--force-text-input</samp>&rsquo; options.  If
standard input conforms to the data file format specification <a href="File-Format.html#File-Format">File Format</a>,
the following effects are possible.
</p>
<ul>
<li> If neither &lsquo;<samp>--choice-of-output</samp>&rsquo; nor
&lsquo;<samp>--force-text-input</samp>&rsquo; is used, the argument to the function will
be given directly by the tree encoded in the data section of the
file. The preamble of the file will be ignored.
</li><li> If the &lsquo;<samp>--choice-of-output</samp>&rsquo; option is used
and the &lsquo;<samp>--force-text-input</samp>&rsquo; option is not used, the argument to
the function will be a pair <code>(<var>preamble</var>,<var>contents</var>)</code>,
where <var>preamble</var> is a list of character strings taken from the
preamble of the file (with leading hashes stripped), and <var>contents</var>
is the tree represented in the data section of the file.
</li><li> If the &lsquo;<samp>--choice-of-output</samp>&rsquo; option is not used
and the &lsquo;<samp>--force-text-input</samp>&rsquo; option is used, the argument to the
function will be the whole file as a list of character strings.  I.e.,
both the preamble and the data sections are included, hashes are not
stripped from the preamble, and the data section is not converted to the
tree it represents.
</li><li> If the &lsquo;<samp>--choice-of-output</samp>&rsquo; option is used
and the &lsquo;<samp>--force-text-input</samp>&rsquo; option is also used, the argument to the
the function will be a pair <code>(nil,<var>contents</var>)</code>, where the
contents are the list of character strings as in the previous case.
</li></ul>

<a name="index-file-format-1"></a>
<p>If standard input does not conform to the data file format specification
in <a href="File-Format.html#File-Format">File Format</a>, then it is assumed to be a text file. The
&lsquo;<samp>--force-text-input</samp>&rsquo; option makes no difference, and there are
only two possible effects, depending on whether
&lsquo;<samp>--choice-of-output</samp>&rsquo; is used. They correspond to the latter two
cases above, where &lsquo;<samp>--force-text-input</samp>&rsquo; is used.
</p>
<a name="index-preamble-1"></a>
<a name="index-text-files-1"></a>
<p>The idea of the &lsquo;<samp>--choice-of-output</samp>&rsquo; option is that it is used
only for applications that are smart enough to be aware of the
<code>(<var>preamble</var>,<var>contents</var>)</code> convention. A non-empty preamble
implies a data file whose contents could be any type, but an empty
preamble implies a text file whose contents can only be a list of
character strings. (In the case of a data file with no preamble, the
list of the empty string is used for the preamble to distinguish it from
a text file.)
</p>
<p>Dumb applications that never want to deal with anything but text files
should be invoked with &lsquo;<samp>--force-text-input</samp>&rsquo;. Otherwise, they have
to be prepared for either text or data as arguments.
</p>
<p>The use of both options at once is unproductive as far as the input
format is concerned, but may be justified when the output is to be a
data file and the input is text only.
</p>
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<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left"> &nbsp; </td>
<td valign="middle" align="left">[<a href="avram.html#Top" title="Cover (top) of document">Top</a>]</td>
<td valign="middle" align="left">[<a href="avram_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
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