Critique this ISR. What is wrong with it?

__interrupt double compute_area(double radius) {
    double area = PI * radius * radius;
    printf("Area = %f", area);
    return area;
}

This ISR has four fundamental problems:

• ISRs cannot return values — the hardware invokes the ISR via the interrupt vector; there is no caller to receive a return value.
• ISRs cannot take parameters — they are triggered by hardware, not called with arguments.
• Floating-point in an ISR — FP operations use shared FPU registers that may not be saved/restored, and they are slow. ISRs should be fast and minimal.
• printf() in an ISR — it is slow, typically not reentrant, and may rely on interrupts itself (UART TX), causing deadlocks.

A proper ISR: takes no parameters, returns void, does minimal work (set a flag, copy data to a buffer), and defers heavy processing to the main loop or an RTOS task.