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<h4 class="subsection">3.4.2 Execution Modes</h4>

<p>Some functions declared in <samp><span class="file">exmodes.h</span></samp> are useful for executing
interactive applications or filter mode transducers in a manner
consistent with the specifications described in the previous chapter.

<div class="defun">
&mdash; Function: void <b>avm_interact</b> (<var>list avm_interactor, int step_mode, int ask_to_overwrite_mode, int quiet_mode</var>)<var><a name="index-avm_005finteract-593"></a></var><br>
<blockquote>
        <p>This function executes an interactive virtual code application. The
parameters have these interpretations.

          <dl>
<dt><var>avm_interactor</var><dd>is the virtual code for a function that performs as specified in
<a href="Output-From-Interactive-Applications.html#Output-From-Interactive-Applications">Output From Interactive Applications</a>. 
<br><dt><var>step_mode</var><dd>will cause all shell commands to be echoed if set to a non-zero
value, and will cause the program to pause after each shell command
until a key is pressed. 
<br><dt><var>ask_to_overwrite_mode</var><dd>can be set to a non-zero value by the caller to cause the program to ask
permission of the user to overwrite any existing files in cases where
the virtual code returns a file list as described in <a href="Mixed-Modes-of-Interaction.html#Mixed-Modes-of-Interaction">Mixed Modes of Interaction</a>. 
<br><dt><var>quiet_mode</var><dd>can be set to a non-zero value to suppress console messages in the case
of file output per <a href="Mixed-Modes-of-Interaction.html#Mixed-Modes-of-Interaction">Mixed Modes of Interaction</a>. 
</dl>

        <p>The meaning of this function is accessible to any reader willing to slog
through <a href="Output-From-Interactive-Applications.html#Output-From-Interactive-Applications">Output From Interactive Applications</a>. The only subtle
point is that <var>avm_interactor</var> parameter in this function
does not correspond to the virtual code application that <code>avram</code>
reads from a virtual code file, but to the result computed when the
application read from the file is applied to the data structure
representing the command line and environment.

        <p>Any of the memory overflows or i/o errors possible with other functions
in the library are possible from this one as well, and will also cause
it to print an error message and halt the program. A badly designed
<a name="index-deadlock-594"></a>virtual code application could cause a deadlock, which will not be
detected or reported
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_trace_interaction</b> ()<var><a name="index-avm_005ftrace_005finteraction-595"></a></var><br>
<blockquote>
        <p>This function enables diagnostic output for the <code>avm_recoverable_interact</code>
function. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_disable_interaction</b> ()<var><a name="index-avm_005fdisable_005finteraction-596"></a></var><br>
<blockquote>
        <p>This function causes <code>avm_interact</code> and <code>avm_recoverable_interact</code>
to terminate with an error instead of executing, as required by the
<code>--jail</code> command line option. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: list <b>avm_recoverable_interact</b> (<var>list interactor, int *fault</var>)<var><a name="index-avm_005frecoverable_005finteract-597"></a></var><br>
<blockquote>
        <p>This function is similar to <code>avm_interact</code> but always closes the
pipe and performs no file i/o, and will return an error message rather
than exiting. Otherwise it returns a transcript of the intereaction as
a list of lists of strings represented as lists of character
encodings.  It implements the <var>interact</var> combinator with the
virtual code for the transducer function given as the parameter.  A
prior call to <code>avm_trace_interaction</code> will cause diagnostic
information to be written to standard output when this function is
executed. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_byte_transduce</b> (<var>list operator</var>)<var><a name="index-avm_005fbyte_005ftransduce-598"></a></var><br>
<blockquote>
        <p>This function executes a filter mode byte transducer application, which
behaves as described in <a href="Byte-Transducers.html#Byte-Transducers">Byte Transducers</a>. The argument is the
virtual code for the application, which would be found in a virtual code
file. There are limited opportunities for i/o errors, as only standard
input and standard output are involved with this function, but fatal
errors due to memory overflow are possible. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_line_map</b> (<var>list operator</var>)<var><a name="index-avm_005fline_005fmap-599"></a></var><br>
<blockquote>
        <p>This function executes line mapped filter mode applications, which are
explained in <a href="Line-Maps.html#Line-Maps">Line Maps</a>. The argument is the virtual code for the
application. Similar comments to those above apply. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_initialize_exmodes</b> ()<var><a name="index-avm_005finitialize_005fexmodes-600"></a></var><br>
<blockquote>
        <p>This function should be called before any of the other functions in this
section in order to initialize some local variables. Results are
undefined if this function isn't called first. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_count_exmodes</b> ()<var><a name="index-avm_005fcount_005fexmodes-601"></a></var><br>
<blockquote>
        <p>This function doesn't do anything in the present version of the library,
but should be called after the last call to any of the other functions
in this section in order to maintain compatibility with future versions,
which may use it for cleaning up local variables. 
</p></blockquote></div>

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