David, On 21/03/2011, at 4:18 PM, David Barbour wrote:
I was giving Control.Arrow a try for a reactive programming system. The arrows are agents that communicate by sending and returning time-varying state. Different agents may live in different 'vats' (event-driven threads) to roughly model distributed computing. For the most part, the state varies asynchronously - i.e. a file updates at a different rate than the mouse position. Anyhow, I ran into a problem: The (***) and (&&&) operations, as specified in Control.Arrow, are inherently synchronization points.
Indeed. Take a look here: http://www.haskell.org/haskellwiki/Research_papers/Monads_and_arrows#Arrows In particular, "ProdArrows -- Arrows for Fudgets" by Magnus Carlsson. cheers peter