title: Evaluate call that contains another call (call within call)
body: <p>I have encountered a snippet of code where call contains another call. For example:</p>
  
  <pre><code>a &lt;- 1
  b &lt;- 2
  # First call
  foo &lt;- quote(a + a)
  # Second call (call contains another call)
  bar &lt;- quote(foo ^ b)
  </code></pre>
  
  <p>We can evaluate calls with <code>eval</code> (<code>eval(foo)</code>), however <code>eval(bar)</code> won't work. This is expected as R tries to run <code>"foo" ^ 2</code> (sees <code>foo</code> as non-numeric object).<br>
  How to evaluate such <em>callception</em>?</p>