content: {-| Ganeti lock-related types and type classes
  
  -}
  
  {-
  
  Copyright (C) 2014 Google Inc.
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  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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  -}
  
  module Ganeti.Locking.Types
    ( Lock
    , lockImplications
    ) where
  
  {-| The type class of being a lock
  
  As usual, locks need to come with an order, the lock order, and
  be an instance of Show, so that malformed requests can meaningfully
  be reported.
  
  Additionally, in Ganeti we also have group locks, like a lock for all
  nodes. While those group locks contain infinitely many locks, the set
  of locks a single lock is included in is always finite, and usually
  very small. So we take this association from a lock to the locks it
  is (strictly) included in as additional data of the type class.
  
  It is a prerequisite that whenever 'a' is implied in 'b', then all locks
  that are in the lock order between 'a' and 'b' are also implied in 'b'.
  
  -}
  
  class (Ord a, Show a) => Lock a where
    lockImplications :: a -> [a]
  