def self_improving_loop(goal):
    """
    Generate a solution to achieve a given goal through iterative improvement.

    Args:
        goal (function): A function that takes an input and returns True if achieved.

    Returns:
        function: The final solution.
    """
    def generate_code():
        return lambda x: x**2

    def test_code(code):
        try:
            return code(5) == 25
        except Exception as e:
            print(f"Error: {e}")
            return False

    while True:
        code = generate_code()
        if test_code(code):
            break
        else:
            # Learn from failure and adjust code generation
            pass
    return code