title: Not able to get a module function working
body: <p>I am trying this simple code to split a string to a list by a separator: </p>
  
  <pre><code>open String;;
  let ss = "/usr/bin/ocaml";;
  let sslist = String.split_on_char '/' ss  in
      print_endline sslist;;
  </code></pre>
  
  <p>It is giving error: </p>
  
  <pre><code>$ ocaml testing.ml
  
  File "testing.ml", line 5, characters 13-33:
  Error: Unbound value String.split_on_char
  </code></pre>
  
  <p>I am sure it is something very basic but I am not able to solve it. Removing <code>open String</code> or using <code>#require "string"</code> also does not work. </p>
  
  <p>Where is the problem and how can it be solved? Thanks for your help.</p>