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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fusion.functional"></a><a href="functional.html" title="Functional">Functional</a></h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="functional/concepts.html">Concepts</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/concepts/callable.html"> Callable Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/reg_callable.html"> Regular Callable
        Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/def_callable.html"> Deferred
        Callable Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/poly.html"> Polymorphic Function
        Object</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/invocation.html">Invocation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/invocation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/invocation/metafunctions.html">Metafunctions</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/adapters.html"> Adapters</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/adapters/fused.html">fused</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_procedure.html">fused_procedure</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_function_object.html">fused_function_object</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_generic.html">unfused_generic</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_lvalue_args.html">unfused_lvalue_args</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_rvalue_args.html">unfused_rvalue_args</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_typed.html">unfused_typed</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/generation.html">Generation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/generation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/generation/metafunctions.html">Metafunctions</a></span></dt>
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<p>
      Components to call functions and function objects and to make Fusion code callable
      through a function object interface.
    </p>
<p>
      /functional.hpp&gt;
    </p>
<a name="fusion.functional.fused_and_unfused_forms"></a><h3>
<a name="id654411"></a>
      <a href="functional.html#fusion.functional.fused_and_unfused_forms">Fused and unfused
      forms</a>
    </h3>
<p>
      What is a function call?
    </p>
<pre class="programlisting">
<span class="identifier">f</span> <span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">,</span><span class="identifier">c</span><span class="special">)</span>
</pre>
<p>
      It is a name and a tuple written next to each other, left-to-right.
    </p>
<p>
      Although the C++ syntax does not allow to replace <tt class="literal">(a,b,c)</tt>
      with some Fusion <a href="sequence.html" title="Sequence">Sequence</a>, introducing
      yet another function provides a solution:
    </p>
<pre class="programlisting">
<span class="identifier">invoke</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">my_sequence</span><span class="special">)</span>
</pre>
<p>
      Alternatively it is possible to apply a simple transformation to <tt class="literal">f</tt>
      in order to achieve the same effect:
    </p>
<pre class="programlisting">
<span class="identifier">f</span> <span class="identifier">tuple</span> <span class="special">&lt;=&gt;</span> f' <span class="special">(</span><span class="identifier">tuple</span><span class="special">)</span>
</pre>
<p>
      Now, <tt class="literal">f'</tt> is an unary function that takes the arguments to
      <tt class="computeroutput"><span class="identifier">f</span></tt> as a tuple; <tt class="literal">f'</tt>
      is the <span class="emphasis"><em>fused</em></span> form of <tt class="computeroutput"><span class="identifier">f</span></tt>.
      Reading the above equivalence right-to-left to get the inverse transformation,
      <tt class="computeroutput"><span class="identifier">f</span></tt> is the <span class="emphasis"><em>unfused</em></span>
      form of <tt class="literal">f'</tt>.
    </p>
<a name="fusion.functional.calling_functions_and_function_objects"></a><h3>
<a name="id654676"></a>
      <a href="functional.html#fusion.functional.calling_functions_and_function_objects">Calling
      functions and function objects</a>
    </h3>
<p>
      Having generic C++ code call back arbitrary functions provided by the client
      used to be a heavily repetitive task, as different functions can differ in
      arity, invocation syntax and other properties that might be part of the type.
      Transporting arguments as Fusion sequences and factoring out the invocation
      makes Fusion algorithms applicable to function arguments and also reduces the
      problem to one invocation syntax and a fixed arity (instead of an arbitrary
      number of arbitrary arguments times several syntactic variants times additional
      properties).
    </p>
<p>
      Transforming an unfused function into its fused counterpart allows n-ary calls
      from an algorithm that invokes an unary <a href="functional/concepts/poly.html" title=" Polymorphic Function
        Object">Polymorphic
      Function Object</a> with <a href="sequence.html" title="Sequence">Sequence</a>
      arguments.
    </p>
<p>
      The library provides several function templates to invoke different kinds of
      functions and adapters to transform them into fused form, respectively. Every
      variant has a corresponding generator function template that returns an adapter
      instance for the given argument.
    </p>
<a name="fusion.functional.making_fusion_code_callable_through_a_function_object_interface"></a><h3>
<a name="id654752"></a>
      <a href="functional.html#fusion.functional.making_fusion_code_callable_through_a_function_object_interface">Making
      Fusion code callable through a function object interface</a>
    </h3>
<p>
      Transforming a fused function into its unfused counterpart allows to create
      function objects to accept arbitrary calls. In other words, an unary function
      object can be implemented instead of (maybe heavily overloaded) function templates
      or function call operators.
    </p>
<p>
      The library provides several adapter variants that implement this transformation,
      ranging from strictly typed to fully generic. The latter provides a reusable,
      approximate solution to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
      Forwarding Problem</a>. Every generic variant has a corresponding generator
      function template that returns an adapter instance for the given argument.
    </p>
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