Re: [Haskell-cafe] One of the new buzz phrases is "Event-Sourcing"; is Haskell suitable for this?

Hi,Marcelo, No. .Acid state is explcitly managed by the process by means of state management primitives In Control.Workflow the state is managed in a implicit way. It is a monad transformer mainly is designed for wrapping IO computations. the lifting primitive, step, store the intermediate result and recover the application state. in acid state the process choose what to write in the state in workflow the state written is the complete state of the process. See the example in the documentation. the process , http://hackage.haskell.org/packages/archive/Workflow/0.7.0.7/doc/html/Contro... import Control.Workflow import Control.Concurrent(threadDelay) import System.IO (hFlush,stdout) mcount n= do step http://hackage.haskell.org/packages/archive/Workflow/0.7.0.7/doc/html/Contro... $ do putStr (show n ++ " ") hFlush stdout threadDelay 1000000 mcount (n+1) return () -- to disambiguate the return type main= exec1 http://hackage.haskell.org/packages/archive/Workflow/0.7.0.7/doc/html/Contro... "count" $ mcount (0 :: Int)

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*runghc demos\sequence.hs*>0 1 2 3 CTRL-C Pressed>>> *runghc demos\sequence.hs*>3 4 5 6 7 CTRL-C Pressed>>> *runghc demos\sequence.hs*>7 8 9 10 11 ...

in subsequent executions the process start to execute IO computations from the last point logged: As the documentation says some side effect can be re-executed after recovery if the log is not complete. This may happen after an unexpected shutdown (in this case Contro-C has been pressed) or due to an asynchronous log writing policy. (see syncWritehttp://hackage.haskell.org/packages/archive/Workflow/0.7.0.7/doc/html/Contro... ) (writing is cached). Althoug this is not event sourcing, The logging and recovery facilities can be used for even sourcing. Alberto 2012/9/30 Marcelo Sousa

Hi,

On Sun, Sep 30, 2012 at 4:22 AM, Alberto G. Corona wrote:

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It´´s a very iteresting concept.

The Workflow Monad transformer [1], in Control.Workflow perform logging and recovery of application istate from the log created. It has no implementation of roll-back or limited recovery upto a point, but this is easy to implement.

Is Control.Workflow similar with acid-state with respect to the way you recovery the current state?

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It also has many inspection and synchronization primitives. It has been used also for translating the log of a program and recovering the state in another machine. The log can be pretty-printed for debugging.

Can you "somehow" recover impure (IO) computations?

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[1] http://hackage.haskell.org/package/Workflow

Regards, Marcelo

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2012/9/30 KC :

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http://martinfowler.com/eaaDev/EventSourcing.html

http://martinfowler.com/articles/lmax.html

-- -- Regards, KC

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-- Alberto.

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-- Alberto.