title: set variable to the same variable modified?
body: <p>I have a program I'm trying to create of a one line text editor
  I've come to a bit of a wall at this point.
  I have a <code>list</code> of letters called <code>left</code> and one called <code>right</code>
  perhaps in a function or a do list how can I set left to <code>left ++ char</code> where char is a user inputted char. I understand it's not possible to modify lists but can I redefine them?
  If this pseudo code helps</p>
  
  <pre><code>left = "hello"
  in = get user input
  left = left ++ in
  </code></pre>
  
  <p>Thanks in advance</p>