Problem 2.2: Mutable Mapping (100 pts)

Implement deep_map_mut(fn, link), which applies a function fn onto all elements in the given linked list link. If an element is itself a non-empty linked list, apply fn to each of its elements, and so on.

Your implementation should mutate the original linked list. Do not create any new linked lists.

Hint: The built-in isinstance function may be useful, but be careful about Link.empty.

>>> s = Link(1, Link(2, Link(3, Link(4))))
>>> isinstance(s, Link)
True
>>> isinstance(s, int)
False
>>> isinstance(Link.empty, Link)
False

def deep_map_mut(fn, link):
    """Mutates a deep link by replacing each item found with the
    result of calling fn on the item.  Does NOT create new Links (so
    no use of Link's constructor)

    Does not return the modified Link object.

    >>> link1 = Link(3, Link(Link(4), Link(5, Link(6))))
    >>> # Disallow the use of making new Links before calling deep_map_mut
    >>> Link.__init__, hold = lambda *args: print("Do not steal chicken!"), Link.__init__
    >>> try:
    ...     deep_map_mut(lambda x: x * x, link1)
    ... finally:
    ...     Link.__init__ = hold
    >>> print(link1)
    <9 <16> 25 36>
    """
    "*** YOUR CODE HERE ***"