Revision a8038349 htools/Ganeti/HTools/Types.hs

b/htools/Ganeti/HTools/Types.hs
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  , Element(..)
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  , FailMode(..)
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  , FailStats
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  , OpResult(..)
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  , OpResult
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  , opToResult
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  , EvacMode(..)
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  , ISpec(..)
......
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-- The failure values for this monad track the specific allocation
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-- failures, so this is not a general error-monad (compare with the
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-- 'Result' data type). One downside is that this type cannot encode a
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-- generic failure mode, hence 'fail' for this monad is not defined
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-- and will cause an exception.
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data OpResult a = OpFail FailMode -- ^ Failed operation
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                | OpGood a        -- ^ Success operation
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                  deriving (Show, Read)
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-- generic failure mode, hence our way to build a FailMode from string
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-- will instead raise an exception.
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type OpResult = GenericResult FailMode
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instance Monad OpResult where


  		





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  (OpGood x) >>= fn = fn x


  		





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  (OpFail y) >>= _ = OpFail y


  		





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  return = OpGood


  		





  
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-- | 'FromString' instance for 'FailMode' designed to catch unintended


  		





  
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-- use as a general monad.


  		





  
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instance FromString FailMode where


  		





  
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  mkFromString v = error $ "Programming error: OpResult used as generic monad"


  		





  
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                           ++ v


  		





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-- | Conversion from 'OpResult' to 'Result'.


  		





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opToResult :: OpResult a -> Result a


  		





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opToResult (OpFail f) = Bad $ show f


  		





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opToResult (OpGood v) = Ok v


  		





  
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opToResult (Bad f) = Bad $ show f


  		





  
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opToResult (Ok v) = Ok v


  		





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-- | A generic class for items that have updateable names and indices.


  		





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class Element a where


  		












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