On Fri, 26 Oct 2012, Brandon Simmons wrote:
Hi everybody, Just discovered all the great discussion here, and although my google-fu turned up no prior discussions on this subject, I apologize if it has already been discussed.
I propose that Chan and TChan should be implemented as a pair of read and write ends, initialized as follows:
newSplitChan :: IO (InChan a, OutChan a)
I've implemented this already here: http://hackage.haskell.org/package/chan-split . You can ignore the type classes I've defined; they're there for my own reasons and not part of the proposal.
I have implemented something similar in plain Haskell 98: http://hackage.haskell.org/package/concurrent-split When using it I found that often there is a clear distinction between input and output end of a channel but sometimes it is not. E.g. a thread might send messages to itself. Of course I could pass around both channel ends in this case. I don't think it is worth to break the API. I am happy with separate packages. If the implementors of Control.Concurrent think that the implementations become cleaner then they might add new modules. This would allow for a smooth transition.