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- <a name="Mixed-Modes-of-Interaction"></a>
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- <h4 class="subsubsection">2.6.4.3 Mixed Modes of Interaction</h4>
- <p>An application is not confined exclusively to line oriented or character
- oriented interaction, but may switch from one style to the other between
- iterations, and signal its choice simply by the format of the data
- structure it returns. If the <var>prompt strings</var> field is non-empty,
- the interaction is line oriented, and if the field is empty, the
- interaction is character oriented. A function using both styles has to
- be prepared for whichever type of data it indicates, either a character or
- a list of character strings as the case may be.
- </p>
- <p>Another alternative is possible if the function returns a data structure
- in the form <code>(<var>files</var>,nil)</code>. This structure includes neither a
- list of command lines nor a list of prompt strings, empty or otherwise,
- but does include a list of quadruples in the <var>files</var> field. The
- quadruples are of the form
- <code>((<var>overwrite</var>,<var>path</var>),(<var>preamble</var>,<var>contents</var>))</code>.
- The fields have the same interpretations as in the output from a
- non-interactive parameter mode application, as described in
- <a href="Output-From-Non_002dinteractive-Applications.html#Output-From-Non_002dinteractive-Applications">Output From Non-interactive Applications</a>, and will cause a list of files to be written in the same way.
- </p>
- <p>As an interactive application is able cause the execution of arbitrary
- shell commands, it doesn’t need <code>avram</code> to write files for it the
- way a non-interactive application does, so this feature does not provide
- any additional capabilities. However, it may be helpful as a matter of
- convenience.
- </p>
- <p>After the files are written, the function will be applied to the same
- result it returned, <code>(<var>files</var>,nil)</code>. There is no direct means
- of preserving unconstrained state information from previous iterations
- in this style of interaction. A likely scenario might therefore be that
- the function returns a file list after finishing its other business, and
- then returns <code>nil</code> on the next iteration to terminate.
- </p>
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