title: string to list of char
body: <p>I want to write a function that taking a string and return a list of char. Here is a function, but I think it is not do what I want ( I want to take a string and return a list of characters).</p>
  
  <pre><code>let rec string_to_char_list s =
      match s with
        | "" -&gt; []
        | n -&gt; string_to_char_list n
  </code></pre>