title: 'Expressions are not allowed at the top level' if the module is not main.swift
body: <p>Is there anything special with a <code>main.swift</code> file?</p>
  
  <p>I have created a command line based project in XCode. If I put an expression <code>println("Hello, World!");</code> in a new swift file says test.swift, I will get the error message:  <code>Expressions are not allowed at the top level</code></p>
  
  <p>However this expression is placed at top level in the main.swift that is created by XCode in the new project. No such exception is flagged by XCode.</p>