Return an error value. If it's really, really important,
write a message to STDERR or a log file (not STDOUT!). Library code
should never,
never,
NEVER die on any error
condition short of the CPU bursting into flames (and even
then it's questionable). What
you consider to be a
fatal error may be a normal condition for the programmer
using your library/module. (Yes, I've had the supreme
displeasure of using a library which "helpfully" terminated
my programs whenever an error occurred without giving me a
chance to detect and correct the situation, or at least
perform a controlled shutdown.)
Oh, and another thing re: the examples under question 4 -
the user should never be subjected to detailed information
about the programmer's mistakes. It will just confuse them.
(*ring* *ring* "Hello, tech support." "Your program just
said, 'Wrong number of parameters! Correct syntax is
my_sub($name,$phone,$address)', but I filled in all the
blanks on the form. And WTF does 'my_sub' mean?")