[Haskell-cafe] Serialization of (a -> b) and IO a

Tillmann Rendel rendel at Mathematik.Uni-Marburg.de
Sat Nov 13 05:27:17 EST 2010

Andrew Coppin wrote:
> [...] if you could send a block of code from one PC to another to
> execute it remotely.

Eden can do this.


Eden is a distributed Haskell: You run multiple copies of the same 
binary on different machines, and you have the (#) operator to apply 
functions *on a remote machine*. So, for example,

   process (map f) # xs

will serialize (map f) and send it over to some other machine. At that 
other machine, (map f) is deserialized and evaluated. In addition, two 
channels between the machines are opened: One for streaming the xs to 
that remote machine where the map is executed, and one for streaming the 
results back.

The process and (#) operators have the following, rather harmless 
looking types:

   process :: (a -> b) -> Process a b
   (#) :: Process a b -> (a -> b)

So no IO around, even if there is serialization and network 
communication going on. If you feel uncomfortable about that, you can 
use instantiate instead:

   instantiate :: Process a b -> a -> IO b

And indeed, (#) is implemented in terms of instantiate and that 
unspeakable source of all false transparency:

   p # x = unsafePerformIO (instantiate p x)


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