Mark Miyashita

def make_fibonacci_stream():
    """
    >>> fib = make_fibonacci_stream()
    >>> fib.first
    0
    >>> fib.rest.first
    1
    >>> fib.rest.rest.first
    1
    """
    "***YOUR CODE HERE***"
    def make_fib_helper(prev, current):
        def compute_rest():
            return make_fib_helper(current, prev + current)
        return Stream(prev, compute_rest)
    return make_fib_helper(0, 1)

Remember, we’re making a stream! That means that we need at least three components. We need to define a compute_rest function that takes in zero arguments and the function should return a Stream object. With these three components in mind, we get to work. First, we realize that we need to keep track of two variables, prev and current. In order to keep track of these variables, we create a helper function that takes in two values. From there, we define our compute_rest function that returns a new Stream. Then, all that’s left is defining the starting values of the make_fib_helper stream. This should be quite natural, we just need to remember the first two elements of the fibonacci sequence!