[danssig]

Or in Common Lisp you would be able to "signal" a condition and then handle the situation. Signal will just do nothing unless some higher level code has an explicit handler for it [1].

[1] I remember reading a MIME encoding library years ago. There was a point where the code would detect an error but if the error was at the end it would just drop that part and write in the last couple of bytes. In this situation, most clients won't care that this is happening but what about those that do? Since this code signalled error by returning NULL there was no way to signal "saw an error, but fixed it". In Common Lisp, signal could have been used for clients that would want to report on this.