const mapNodeValue = <T, R>(mapFn: (value: T) => R) => (node: TreeNode<T>): TreeNode<R> =>
({ ...node, value: mapFn(node.value) });
const mapNodeValue = <T, R>(mapFn: (value: T) => R) => (node: TreeNode<T>): TreeNode<R> =>
({ ...node, value: mapFn(node.value) });