Ocaml Phrasebook (part 5)

Unions are different, and it's important.

template <typename T>            type 'a tree =   
union tree {                          Branch of ('a tree * 'a tree)
  pair < tree <T> &,                | Node of 'a  
         tree <T> & > branch;    
  T & node;
};

Why is the difference important?
Because the union elements on the right are disjoint.
You cannot treat a Node x as a Branch (x, y).
You have to match a 'a tree value against its constructors.
Like this:

match somevalue with
   Branch (x,y) -> frobnicate_branch x y
 | Node x       -> frobnicate_node x