title: How can I make a directed arc of a circle (or a directed curve)?
body: <p>I'd like to display a directed circular arc in Mathematica, using something as simple as <code>Arrow</code>. The best I have been able to come up with is this example that nails an <code>Arrow</code> onto one end of a circular arc. But I suspect there is a more direct way to achieve the same effect.</p>
  
  <pre><code>start=\[Pi];
  Manipulate[
  Graphics[{
     Arrow[{{Cos[\[Theta] + If[\[Theta] &lt; start, .01, -.01]], 
             Sin[\[Theta] + If[\[Theta] &lt; start, .01, -.01]]}, 
            {Cos[\[Theta]], Sin[\[Theta]]}}],
     Circle[{0, 0}, 1, {start, \[Theta]}]},
  PlotRange -&gt; 2], 
  {{\[Theta], .7 start}, 0, 2 start} 
             ]
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/lOWYu.png" alt="arrow"></p>
  
  <p><code>Arrow</code> accepts <code>BSplineCurves</code> and <code>BezierCurves</code>but I can't get them to stay on a circular arc.  <code>Tube</code> accepts the formula for a curve in 3D but I can't figure out how to get it to work in 2D.</p>
  
  <p>All suggestions are welcome.  If your solution works for <em>any</em> <em>2D curve</em>, all the better!</p>
  
  <hr>
  
  <h3>Epilogue:</h3>
  
  <p>I learned quite a bit from the suggestions:
  Mark McClure showed that <code>Arrow</code> itself can handle the demands when given a list of points.</p>
  
  <p>yoda gave a fairly general solution using ParametricPlot.</p>
  
  <p>I ended up finding belisarius' suggestions the most helpful.  His approach was to work on minor variations of familiar graphical objects.  In the end, I cautiously chose to define a new object, <code>arcArrow</code>, that employs the parameters of <code>Circle</code>: center, radius, {start,finish}.  <code>Unprotect</code> still scares me!  Anyway, here's what I settled with. I also stubbornly held on to some features of my original approach.</p>
  
  <pre><code>Manipulate[
   Graphics[{  
     arcArrow[center, radius, {start, end}],
     PointSize[Large], Blue, If[showCenter, Point[center]]},
    PlotRange -&gt; p, ImageSize -&gt; 250],
   {{start, \[Pi]/2}, -2 \[Pi], 2 \[Pi], ImageSize -&gt; Small},
   {{end, 0}, -2 \[Pi], 2 \[Pi], ImageSize -&gt; Small},
   {{radius, 1}, 1/2, 4, ImageSize -&gt; Small},
   {{center, {0, 0}}, {-p, -p}, {p, p}, Slider2D},
   {showCenter, {True, False}},
  
   Initialization :&gt; {p = 3;
     arcArrow[a_, r_, {start_, end_}] :=
      {Circle[a, r, {start, end}], 
       Arrowheads[Medium],
       Arrow[{a + r {Cos[end + If[end &lt; start, .01, -.01]], 
                     Sin[end + If[end &lt; start, .01, -.01]]}, 
              a + r {Cos[end], Sin[end]}}]} }]
  </code></pre>
  
  <p><img src="https://stack.imgur.com/9mVgu.png" alt="final version"></p>
  
  <hr>