Simon Marlow wrote:
DiffArray is an example of a good use for unsafePerformIO: it uses imperative operations to implement a pure API. The DiffArray is made of mutable objects under the hood, but as far as the programmer is concerned it behaves just like a pure Array.
I'd like to ask a general question about unsafePerformIO: What exactly does unsafe mean? Just "impure" or rather "may lead to all kinds of problems, you better don't use this"? After a few experiments, I stopped using unsafePerformIO for disk access because it just segfaulted too much. I'm not 100% sure if unsafePerformIO was the culprit though; I did a lot of restructuring while eliminating it, so I might have inadvertently removed the real cause for the crashes in the process. -Stefan