title: Using the in keyword in OCAML
body: <p>I am confused what the keyword <code>in</code> does in OCAML. When do i need to use it ?
  The only example I came close to understanding is :</p>
  
  <pre><code>let quit_loop = ref false in
  while not !quit_loop do
    print_string "Have you had enough yet? (y/n) ";
    let str = read_line () in
    if str.[0] = 'y' then
      quit_loop := true
  done;;
  </code></pre>
  
  <p>or </p>
  
  <pre><code>let x = 10 in
  let y = 20 in
  x + y ;;
  </code></pre>
  
  <p>what does in indicate here ?</p>