title: Tcl info exists
body: <p>I have a curious case of Tcl that perhaps I just don't understand.
  The following code is done at the top level (not inside of any procedure):</p>
  
  <pre><code>if {![info exists g_log_file_name]} {
      set g_log_file_name "default.txt"
  }
  </code></pre>
  
  <p>What I hope it would do is to declare a global variable with some value if it wasn't declared yet (which can be done at some other script or C application). However, the if statement <em>always</em> false. I ran on Tcl 7.4.</p>
  
  <p>What may be the problem?</p>
  
  <p>Thank you so much.</p>