Invisible wrote:
> More succinctly: In OO, trees are usually mutable. In Haskell, trees are 
> usually immutable.

Not that so much as identity is an important aspect of OO, where it isn't in 
functional programming. Two different objects with exactly the same value 
are nevertheless not interchangable.

> A bigger part of it is that, while essentially Haskell has pointers, 
> null pointers are explicitly prohibited.

You could always have Branch hold a couple of Maybe Leaf's.

-- 
Darren New, San Diego CA, USA (PST)
   The question in today's corporate environment is not
   so much "what color is your parachute?" as it is
   "what color is your nose?"

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