title: check if argument is not a list , then display message if it isnt a list
body: <p>I have an argument called "evens" and all it does it get the even elements in a list, and it works fine with lists. But when passed in a atom like 'a, it crashes and says "<em>The object a, passed as the first argument to cdr, is not the correct type</em>. " now i don't want this function to handle atoms only list . </p>
  
  <p>I have tried this but it seems to be wrong , this is kinda what im trying to do but still need some guidance. </p>
  
  <pre><code>    (IF  (NOT(LIST? lis)) "Enter valid list" ) =&gt; "Enter valid list" )
  </code></pre>
  
  <p>So how can i check if something that is not a list is being passed in. And if it is how do i display some kind of text message if it isn't a list? </p>