On Sat, 2011-10-01 at 02:16 -0700, Fred Smith wrote:
In seems to me that in cloud haskell library the function's closures can be computed only with top-level ones, is it possible to compute the closure at runtime of any function and to send it to another host?
The current rule is a bit overly restrictive, true. But I just wanted to point out that there is a good reason for having *some* restriction in place. There are certain types that should *not* be sent to other processes or nodes. Take MVar, for example. It's not clear what it would mean to send an MVar over a channel to a different node. By extension, allowing you to send arbitrary functions not defined at the top level is also problematic, because such functions might close over references to MVars, making them essentially a vehicle for smuggling MVars to new nodes. And since the types of free variables don't occur in the types of terms, there is no straight-forward Haskell type signature that can express this limitation. So the compiler is obliged to specify some kind of sufficient restrictions to prevent you from sending functions that close over MVar or other node-specific types. For now, you'll have to move all of your functions to the top level. Hopefully, in the future, some relaxation of those rules can occur. -- Chris