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<h4 class="subsection">2.7.16 Interfaces to External Code</h4>

<p>A few other combinators have been incorporated into the virtual
machine as alternatives to the style of interactive applications
described in <a href="Output-From-Interactive-Applications.html#Output-From-Interactive-Applications">Output From Interactive Applications</a>. These make it
possible to interface with external libraries and applications either
by a simple function call, or by executing a run-time generated
transducer as described previously. In either case, there is no need
for any particular command line options to specify interactive
invocation, nor for the application to be designed that way from the
outset. Existing virtual code applications may therefore be enhanced
to make use of these features without radical changes.

   <p>To account for these additional capabilities, it is not entirely
adequate to continue defining the virtual machine semantics in terms
of a mathematical function, but it is done nevertheless due to the
lack of any appealing alternative. Although most library functions are
in fact functions in the sense that their outputs are determined by
their arguments, they defy a concise specification within the present
mathematical framework, especially insofar as they may involve finite
precision floating point numbers. More problematically, the effect of
interaction with a shell is neither well defined nor deterministic. 
The descriptions that follow presuppose a computational procedure
associated with the following definitions but leave its exact nature
unspecified.

<ul class="menu">
<li><a accesskey="1" href="Library-combinator.html#Library-combinator">Library combinator</a>
<li><a accesskey="2" href="Have-combinator.html#Have-combinator">Have combinator</a>
<li><a accesskey="3" href="Interaction-combinator.html#Interaction-combinator">Interaction combinator</a>
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