title: Logical not operator
body: <p>Coming from C/C++ land, I am wondering why the following does not work:</p>
  
  <pre><code>set a 111
  if {! $a eq {} } {
    puts hi
  }
  </code></pre>
  
  <p>I know if I change the 2nd line to <code>if { $a ne {} } {</code> then it is fine, but cannot wrap my head around why "!" does not work.</p>