test_call_graph.py

# singleton.py
class Logger:
    """Simple singleton logger."""
    _instance = None
    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
            cls._instance.logs = []
        return cls._instance

    def log(self, msg):
        self.logs.append(msg)
        print(f"[LOG] {msg}")

# recursion.py
def factorial(n):
    """Classic recursion."""
    logger = Logger()
    logger.log(f"factorial({n})")
    if n <= 1:
        return 1
    return n * factorial(n - 1)

# mutual_recursion.py
def is_even(n):
    """Mutual recursion with is_odd."""
    logger = Logger()
    logger.log(f"is_even({n})")
    if n == 0:
        return True
    return is_odd(n - 1)

def is_odd(n):
    logger = Logger()
    logger.log(f"is_odd({n})")
    if n == 0:
        return False
    return is_even(n - 1)

# callbacks.py
def apply_callback(cb, value):
    """Call any function cb on value."""
    return cb(value)

# closures.py
def make_multiplier(factor):
    """Return a callback that multiplies by factor."""
    def multiplier(x):
        return x * factor
    return multiplier

# cycle.py
def f1(x):
    logger = Logger()
    logger.log(f"f1({x}) → f2({x + 1})")
    return f2(x + 1)

def f2(x):
    logger = Logger()
    logger.log(f"f2({x}) → f3({x * 2})")
    return f3(x * 2)

def f3(x):
    logger = Logger()
    logger.log(f"f3({x}) → f1({x - 3}) or back")
    if x > 50:
        return x
    return f1(x - 3)

# generator.py
def countdown(n):
    """A simple generator."""
    while n > 0:
        Logger().log(f"yielding {n}")
        yield n
        n -= 1
    yield "done"

def doit():
    logger = Logger()
    logger.log("Starting main")

    # 1. Recursion
    print("5! =", factorial(5))

    # 2. Mutual recursion
    for i in range(5):
        print(i, "is_even?", is_even(i))

    # 3. Callbacks & closures
    doubler = make_multiplier(2)
    print("Double 7 via apply_callback:", apply_callback(doubler, 7))
    print("Square 4 directly:", apply_callback(lambda x: x*x, 4))

    # 4. Three‐function cycle (stops when >50)
    result = f1(10)
    print("Cycle result:", result)

    # 5. Generator usage
    for item in countdown(3):
        print("countdown:", item)

    logger.log("Main finished")


if __name__ == "__main__":
    doit()