title: Prolog read_file_to_string/3
body: <p>When I call the function read_file_to_string/3 in prolog, why am I getting this error:</p>
  
  <pre><code>ERROR: toplevel: Undefined procedure: read_file_to_string/3(DWIM could not correct goal).
  </code></pre>
  
  <p>I have tried calling it from a file that successfully compiles, but I get the same error.</p>
  
  <p>Thank you.</p>