title: R get argument names from function call
body: <p>I'd like to get  argument names from function call:</p>
  
  <pre><code>testFun &lt;- function(x = 1:20, z = list(a = 1, b = 2)) x %&gt;% sin %&gt;% sum
  
  getArgNames &lt;- function(value) {
    # function should return all arguments names - in this case c("x", "z")
  
  }
  arg.names &lt;- getArgNames(testFun())
  </code></pre>
  
  <p>And it is important to not to evaluate function before getting argument names. Any ideas?</p>