title: Setting language with #lang in the REPL
body: <p>I would like to set the language in the REPL on the fly, with <code>#lang</code>, not using "-I" command-line argument. But this gives me the error "read: #lang not enabled in the current context".</p>
  
  <p>Is there a command-line switch that I'm missing? Or maybe a ",metacommand" I can use? The reason I need this is because I would like to be able to send an Emacs buffer to the Racket REPL, but that won't work if the file starts with <code>#lang</code>.</p>