On 02/24/10 05:07, Simon Marlow wrote:
Simon just pointed out to me that this is quite closely related, though more general:
http://hackage.haskell.org/package/stm-io-hooks http://www.haskell.org/haskellwiki/New_monads/MonadAdvSTM
Because of those ideas that are already floating around, I think this one is misleading. In those, the afterCommit::IO(something)->STM(something) means even if it's not the last statement in the monad, to execute the IO when the transaction commits. Which has notable effects on the compositionality of STM (not sure about "good" or "bad" effects, but it's notable). As a coder, instead of Left and Right or atomicallyIO/afterCommit, I think I'd tend to write those functions inlined where it's readable; join{-IO-} $ atomically $ do{-STM-} ... return $ do{-IO-} ... ... (I do use that sort of which-monad-is-it comment in my code whenever it's not utterly obvious... Haskell doesn't provide any equally concise way to write those notes such that it will be checked by the compiler, sadly.) -Isaac