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avram


			
				
					
						
						
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<h4 class="subsection">2.6.4 Output From Interactive Applications</h4>

<p><a name="index-g_t_0040code_007binteractive_007d-command-line-option-228"></a><a name="index-g_t_0040code_007bstep_007d-command-line-option-229"></a>Parameter mode applications invoked with either of the
<samp><span class="option">--interactive</span></samp> or <samp><span class="option">--step</span></samp> options are
required to take the data structure described in <a href="Input-Data-Structure.html#Input-Data-Structure">Input Data Structure</a> as an
argument but to return the virtual code for a function that will observe
<a name="index-shell-230"></a>a certain protocol allowing shell commands to be executed on its
behalf. The intent is that the virtual code file doesn't contain the
real application <em>per se</em>, but only something that builds the real
one on the fly using configuration information from the input files and
command line options.

   <p>The format of the result returned by an interactive application, being a
virtual code application itself, requires a full exposition of the
virtual machine code semantics. This subject is deferred to <a href="Virtual-Code-Semantics.html#Virtual-Code-Semantics">Virtual Code Semantics</a>. 
The remainder of this section describes the protocol followed by the
function returned by the interactive application rather than the
application itself.

   <p>Similarly to the case of a byte transducer described in <a href="Byte-Transducers.html#Byte-Transducers">Byte Transducers</a>,
the basic pattern of interaction between <code>avram</code> and the function
is a cycle of invocations. In general terms, the function is applied to
a <code>nil</code> argument initially, and expected to return an initial state
and initial output. Thereafter, the function is applied to a pair of the
state returned on the previous iteration, and the next installment of
input. The function returns further output and a new state, and the
cycle continues until the function returns a value of <code>nil</code>, at
which time the computation terminates.

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<li><a accesskey="2" href="Character-Oriented-Interaction.html#Character-Oriented-Interaction">Character Oriented Interaction</a>
<li><a accesskey="3" href="Mixed-Modes-of-Interaction.html#Mixed-Modes-of-Interaction">Mixed Modes of Interaction</a>
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