[Haskell-cafe] A program which never crashes (even when a function calls "error")

[It is a philosophical question, not a practical programming problem.] I'm used, in imperative programming languages with exceptions (like Python) to call any function without fear of stopping the program because I can always catch the exceptions with things like (Python): while not over: try: code which may raise an exception... except Exception e: do something clever How to do it in Haskell? How can I call functions like Prelude.head while being sure my program won't stop, even if I call head on an empty list (thus calling "error")?