title: OCaml syntax error in type declaration
body: <p>I'm new to OCaml and I have no clue why this is giving me a syntax error: </p>
  
  <pre><code>type ('nonterminal, 'terminal) pe =
  | Empty
  | T of t 
  | N of n
  | Seq of list
  | Choose of list
  | Star of e
  | Not of e;;
  
  type ('nonterminal, 'terminal) pe_tree = 
  | Is_empty 
  | Leaf of t 
  | Node of (n,tree) 
  | Sequence of list 
  | Repeat of list 
  | Is_not of e;;
  </code></pre>
  
  <p>All it's saying is that there's a syntax error on line 14 characters 0-1 (which is where <code>| Sequence of list</code> is) and I can't figure out why!</p>