[-haskell]
On Wed, Apr 21, 2010 at 5:54 PM, Heinrich Apfelmus
David Anderson wrote:
Dear Haskellers,
I'm happy, and only slightly intimidated, to announce the initial release of forkable-monad.
The short version is that forkable-monad exports a replacement forkIO that lets you do this:
type MyMonad = ReaderT Config (StateT Ctx IO)
startThread :: MyMonad ThreadId startThread = forkIO threadMain
threadMain :: MyMonad () threadMain = forever $ liftIO $ putStrLn "Painless monad stack forking!"
Note the lack of monad stack deconstruction and reconstruction to transport it over to the new thread. You'll find the details in the Haddock documentation for the module.
Nice work!
It appears to me that this is subsumed by the recent MonadMorphIO proposal that Anders Kaseorg came up with, though?
http://article.gmane.org/gmane.comp.lang.haskell.libraries/12902
fork :: MonadMorphIO m => m () -> m () fork m = morphIO $ \down -> forkIO (down m >> return ()) >> down (return ())
Hmm, quite possibly. It is also quite similar to another implementation of forkable monad stacks I came across after finishing this first version of the library, and to what I had tentatively called "unliftIO" with a slightly different type, in another experiment in messing with forking monad stacks. So, it seems that I am reinventing wheels that others have generalized better :-). That's fine, it's the expected result of launching and iterating, especially given my current command of Haskell. So I should now focus on reducing the reinvention. Most of the discussion that followed the message that you linked is currently beyond my understanding of category theory. However, I should probably go and talk to the maintainer of MonadCatchIO-* about extracting something like MonadMorphIO into a package, and making both their exception handling modules and this forking module reuse it. Thanks for the pointer! - Dave
Regards, Heinrich Apfelmus
-- http://apfelmus.nfshost.com
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