7 Nov
2003
7 Nov
'03
6:45 a.m.
This is one good reason they have to be protected by MVars
Forgive my stupidity, but arn't the MVar operations (takeMVar, putMVar) IO operation, therefore the locks must be in the IO monad, therefore the code acting on the DiffArray should be in the IO monad... otherwise they can't use the MVar calls?
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. Cheers, Simon