title: scheme call/cc for handling errors
body: <p>I have a Scheme application that accepts some user input, computes, and gives some output.  I would like to make it more robust by enabling some kind of error handling and a way to exit smoothly.  Call with current continuation seems to be the thing to fill this gap here, but I'm not quite sure how to go about implementing it.</p>
  
  <p>As of now, if the user enters some non-valid input, the program will crash and exit.  I would simply like to keep the user in the application and give an error message instead.  Here is an outline of my method, but I'm not sure where to implement it so that if an error occurs that would normally crash the system, just gives an error and keeps them in the program.</p>
  
  <pre><code>  (define (handle_err)
      (call/cc
       (lambda (a)
      (display "exception handled: a"))))
  </code></pre>
  
  <p>I would also like a clean exit from the program.  That is, not a crash exit, nor a break.  I would like the user to type "leave", have the program close and return to the interpreter.  My outline looks much like the above, but it doesn't have the user leave the program, it just takes him back to the input prompt.  </p>
  
  <p>Any ideas are appreciated.</p>