Write a Fibonacci number generator.

The Fibonacci number generator is a function that returns the next number in the sequence each time it is called, where each number is the sum of the two preceding ones, starting from 0 and 1.

Example in Python:

def fibonacci_generator():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a + b

# Usage:
gen = fibonacci_generator()
for _ in range(10):
    print(next(gen))

This generator infinitely produces Fibonacci numbers on demand.