The node will have one child. It owns it.
| NodeUn (UnOper* op, Node* node, unsigned line)
Caller must not delete / modify pointers.
|op||unary operation associated with node.|
|node||child of node -- argument of operation.|
|line||line of configuration where node was created.|
| ~NodeUn ()
| DEFINE_VISITABLE ()
|const UnOper& op ()
Returns: unary operation associated with node.
|Node& node ()
Returns: argument of unary operation.