2009/12/07 klondike
Well I got used to going back to the previous state without crashing when I got a precondition violation due to user input. Though I assume that was asking a bit too much of Haskell.
It's too much to ask of partial functions. If you want to state your preconditions and rollback in an appropriate monad, that's of a horse of a different color.
Of course crashing the whole program as default behaviour is a better way to solve the problem.
If you're not working in a side-effecting or sequential subset of the language, you can't really expect to have a consistent notion of the state "before" the crash. It's a declarative, lazy language, after all. Consider, also, that a crash is just one of the problems you get with bad input; another one is infinite loops. As Henning Thielemann points out in his wiki article, you can't expect to catch those as they don't throw exceptions or cause any errors! You need to validate the input or use a timer in that case. Relying on the program to crash in a timely manner if something is wrong with the input is not a strategy that is going to go the distance. -- Jason Dusek