On Sep 4, 2008, at 12:50 PM, minh thu wrote:
I'd have thought you wanted "IORef (Maybe Thing)", which says that
the
pointer always exists, but may not point to anything. On the other
hand
"Maybe (IORef Thing)" says that the pointer may or may not exist.
Yes, someone else said it too. But you saiy that regarding the
pointer. If you
look at the thing the pointer (if any) points at, what's the
difference ?
Either there is none : Nothing or IORef Nothing, or there is one :
Just (IORef 5)
or IORef (Just 5).
There is still a difference. With Maybe (IORef a), the nothingness is
expressed only locally, but with IORef (Maybe a), the nothingness can
be shared and mutated by any other IORefs that point to it as well.
- Jake McArthur
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