Beispiel: Einfügen in Baum

• destruktiv:

  interface Tree<K> { void insert (K key); }
  Tree<String> t = ... ; 
  t.insert ("foo");
  

• persistent (Java):

  interface Tree<K> { Tree<K> insert (K key); }
  Tree<String> t = ... ; 
  Tree<String> u = t.insert ("foo");
  

• persistent (Haskell):

  insert :: Tree k -> k -> Tree k