Re: [Haskell-cafe] Monads
Vasili I. Galchin wrote: I would an examples of monads that are pure, i.e. no side-effects. One view of programming in monadic style is: You call return and = all the time. (Either you call it directly, or do notation calls it for you). So if you want to understand whether a monad has side-effects, you should look at the implementation of return and =. If the implementation of return and = is written in pure Haskell (without unsafePerformIO or calling C code etc.), the monad is pure. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monads
On 12-09-29 09:57 PM, Vasili I. Galchin wrote: I would an examples of monads that are pure, i.e. no side-effects. What does side effect mean, to you? Definition? Because some people say State has no side effect, and some other people say State has side effects. The two groups use different definitions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] One of the new buzz phrases is Event-Sourcing; is Haskell suitable for this?
Hi, On Sun, Sep 30, 2012 at 4:22 AM, Alberto G. Corona agocor...@gmail.com wrote: 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? 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? [1] http://hackage.haskell.org/package/Workflow Regards, Marcelo 2012/9/30 KC kc1...@gmail.com: http://martinfowler.com/eaaDev/EventSourcing.html http://martinfowler.com/articles/lmax.html -- -- Regards, KC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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/Control-Workflow.html 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/Control-Workflow.html#v:step $ do putStr (show n ++ ) hFlush stdout threadDelay 100 mcount (n+1) return () -- to disambiguate the return type main= exec1 http://hackage.haskell.org/packages/archive/Workflow/0.7.0.7/doc/html/Control-Workflow.html#v:exec1 count $ mcount (0 :: Int) *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/Control-Workflow.html#v:syncWrite ) (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 dipyt...@gmail.com Hi, On Sun, Sep 30, 2012 at 4:22 AM, Alberto G. Corona agocor...@gmail.com wrote: 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? 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? [1] http://hackage.haskell.org/package/Workflow Regards, Marcelo 2012/9/30 KC kc1...@gmail.com: http://martinfowler.com/eaaDev/EventSourcing.html http://martinfowler.com/articles/lmax.html -- -- Regards, KC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] One of the new buzz phrases is Event-Sourcing; is Haskell suitable for this?
On 09/30/2012 02:46 AM, KC wrote: http://martinfowler.com/eaaDev/EventSourcing.html http://martinfowler.com/articles/lmax.html Sure, why not? See http://hackage.haskell.org/package/cqrs-0.8.0 and http://hackage.haskell.org/package/cqrs-example-0.8.0 for an example application. I should note that the cqrs package API is by no means finalized; there are some limitations(*) to the current implementation, but I've not had time to actually get rid of those limitations. (*) The major ones being the requirement for a global version number and lack of streaming event sourcing. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monads
On 9/30/12 7:00 AM, Tillmann Rendel wrote: Vasili I. Galchin wrote: I would an examples of monads that are pure, i.e. no side-effects. One view of programming in monadic style is: You call return and = all the time. (Either you call it directly, or do notation calls it for you). So if you want to understand whether a monad has side-effects, you should look at the implementation of return and =. If the implementation of return and = is written in pure Haskell (without unsafePerformIO or calling C code etc.), the monad is pure. I'm not sure return and bind will give you the information you seek, however. In order to obey the monad laws, return and bind must be (for all intents and purposes) pure. The place to look for impurities is the primitive operations of the monad; i.e., those which cannot be implemented using return and bind. These are the operations which take you out of a free monad and the operations which must be given some special semantic interpretation. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Possible bug in Criterion or Statistics package
Aleksey Khudyakov alexey.sklad...@gmail.com writes: On 13.08.2012 19:43, Ryan Newton wrote: Terrible! Quite sorry that this seems to be a bug in the monad-par library. I'm copying some of the other monad-par authors and we hopefully can get to the bottom of this. If it's not possible to create a smaller reproducer, is it possible to share the original test that triggers this problem? In the meantime, it's good that you can at least run without parallelism. Here is slightly simplified original test case. By itself program is very small but there is statistics and criterion on top of the monad-par Failure occurs in the function Statistics.Resampling.Bootstrap.bootstrapBCA. However I couldn't trigger bug with mock data. Has there been any progress or an official bug report on this? Cheers, - Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monads
On Sep 30, 2012 10:56 AM, Albert Y. C. Lai tre...@vex.net wrote: On 12-09-29 09:57 PM, Vasili I. Galchin wrote: I would an examples of monads that are pure, i.e. no side-effects. What does side effect mean, to you? Definition? When discussing monads, at least, a side effect is an effect that is triggered by merely evaluating an expression. A monad is an interface that decouples effects from evaluation. Because some people say State has no side effect, and some other people say State has side effects. The two groups use different definitions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monads
On Sun, Sep 30, 2012 at 6:33 PM, Jake McArthur jake.mcart...@gmail.com wrote: On Sep 30, 2012 10:56 AM, Albert Y. C. Lai tre...@vex.net wrote: On 12-09-29 09:57 PM, Vasili I. Galchin wrote: I would an examples of monads that are pure, i.e. no side-effects. What does side effect mean, to you? Definition? When discussing monads, at least, a side effect is an effect that is triggered by merely evaluating an expression. A monad is an interface that decouples effects from evaluation. Ohh, I like that quote.., that's another good one.. kris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] One of the new buzz phrases is Event-Sourcing; is Haskell suitable for this?
On Sat, Sep 29, 2012 at 8:46 PM, KC kc1...@gmail.com wrote: http://martinfowler.com/eaaDev/EventSourcing.html http://martinfowler.com/articles/lmax.html This notion of Capture all changes to an application state as a sequence of events sounds a lot like what John Carmack did in Quake 3 [1]: I settled on combining all forms of input into a single system event queue, similar to the windows message queue. My original intention was to just rigorously define where certain functions were called and cut down the number of required system entry points, but it turned out to have much stronger benefits. [1]: http://www.team5150.com/~andrew/carmack/johnc_plan_1998.html#d19981014 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monads
On 12-09-30 06:33 PM, Jake McArthur wrote:
When discussing monads, at least, a side effect is an effect that is
triggered by merely evaluating an expression. A monad is an interface
that decouples effects from evaluation.
I don't understand that definition. Or maybe I do subconsciously.
I have
s :: State Int ()
s = do { x - get; put (x+1) }
Is there an effect triggered by merely evaluating s?
I have
m :: IO ()
m = if True then putStrLn x else putChar 'y'
Is there an effect triggered by merely evaluating m?
What counts as evaluate?
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