Re: Immutability -- more ideas

[Araq]

That still doesn't solve the problem well, in my opinion. `select` is the same 
as `findNode` and it's up to the caller whether this node is then updated or 
not. If we do `var n = findNode(root)` it's fine to assume that `n` aliases 
something in `root`, it's a good default. The fact that `construct` constructs 
a new node needs to be communicated.