title: setClass not found when running R script from command line
body: <p>I have simple R script which trying to Define class.
        example.R   </p>
  
  <pre><code> Tuple &lt;- setClass("Tuple",
              slots = c(
                id="character",
                comp="character",
                stream="character",
                task="character",
                output="vector",
                anchors="vector"
                  )
              );
  </code></pre>
  
  <p>when i run Rscript example.R .
    i am getting an error saying below </p>
  
  <p>Error in eval(expr, envir, enclos) : could not find function "setClass"
    Calls: source -> withVisible -> eval -> eval</p>
  
  <p>can any one help? </p>