title: How to re-prompt for user input in tcl
body: <p>I have a simple prompt for user input as the following:</p>
  
  <pre><code>Is this correct? (Y/N): 
  </code></pre>
  
  <p>This prompt should only take either a <code>Y</code> or a <code>N</code> and should re-prompt the user if any other input has been entered.</p>
  
  <p>Could someone please show me a snippet of code on how this can be done? I am still very new with Tcl.</p>