Revision fb54b24a src/Ganeti/BasicTypes.hs

b/src/Ganeti/BasicTypes.hs
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  ) where
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import Control.Applicative


  		





  
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import Control.Exception (try)


  		





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import Control.Monad


  		





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import Control.Monad.Error.Class


  		





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import Control.Monad.Trans


  		





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instance MonadTrans (ResultT a) where


  		





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  lift = ResultT . liftM Ok


  		





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-- | The instance catches any 'IOError' using 'try' and converts it into an


  		





  
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-- error message using 'strMsg'.


  		





  
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--


  		





  
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-- This way, monadic code within 'ResultT' that uses solely 'liftIO' to


  		





  
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-- include 'IO' actions ensures that all IO exceptions are handled.


  		





  
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--


  		





  
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-- Other exceptions (see instances of 'Exception') are not currently handled.


  		





  
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-- This might be revised in the future.


  		





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instance (MonadIO m, Error a) => MonadIO (ResultT a m) where


  		





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  liftIO = lift . liftIO


  		





  
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  liftIO = ResultT . liftIO


  		





  
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                   . liftM (either (failError . show) return)


  		





  
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                   . (try :: IO a -> IO (Either IOError a))


  		





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instance (Monad m, Error a, Monoid a) => MonadPlus (ResultT a m) where


  		





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  mzero = ResultT $ return mzero


  		












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