-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Test instance context
--   
--   Use these functions to decide an a not-quite naive fashion whether an
--   instance already exists that satisfies a given context. This can be
--   used to decide whether an instance needs to be generated, as in
--   th-reify-many. Known limitation: the instances inserted into the
--   InstMap are not fully recognized when computing the context.
@package th-context
@version 0.22


-- | Compute whether any existing instance satisfies some context in a
--   nearly correct fashion. <tt> instance A m =&gt; B m where ... </tt> I
--   say "nearly correct" because there are cases which are not handled
--   exactly the way GHC behaves, which may lead to false (positives?
--   negatives?)
module Language.Haskell.TH.Context
type InstMap = Map (E Pred) [DecStatus InstanceDec]

-- | Did we get this instance from the Q monad or does it still need to be
--   spliced?
data DecStatus a

-- | An instance we found in the Q monad
Declared :: a -> DecStatus a
[instanceDec] :: DecStatus a -> a

-- | An instance we inserted via tellInstance
Undeclared :: a -> DecStatus a
[instanceDec] :: DecStatus a -> a

-- | Like <a>qReifyInstances</a>, looks up all the instances that match the
--   given class name and argument types. Unlike <a>qReifyInstances</a>,
--   only the ones that satisfy all the instance context predicates in the
--   environment are returned. If there is already an instance that
--   satisfies the predicate built from the name and types it is returned.
--   If not, this new predicate is inserted into the state monad
--   <a>InstMap</a>, associated with an empty list of predicates, and the
--   empty list is returned. Later the caller can use <a>tellInstance</a>
--   to associate instances with the predicate.
reifyInstancesWithContext :: (DsMonad m, MonadStates InstMap m, MonadStates ExpandMap m) => Name -> [Type] -> m [InstanceDec]

-- | Declare an instance in the state monad, marked Undeclared. After this,
--   the instance predicate (constructed from class name and type
--   parameters) will be considered part of the context for subsequent
--   calls to reifyInstancesWithContext.
tellInstance :: (DsMonad m, MonadStates InstMap m, Quasi m, MonadStates ExpandMap m) => Dec -> m ()

-- | After all the declared and undeclared instances have been added to the
--   instance map using tellInstance, this returns the undeclared instances
--   only, not the ones that were discovered by reifyInstances, and tells
--   them to the writer monad.
tellUndeclared :: (MonadWriter [Dec] m, MonadStates InstMap m) => m ()
instance GHC.Show.Show a => GHC.Show.Show (Language.Haskell.TH.Context.DecStatus a)
instance Language.Haskell.TH.Ppr.Ppr a => Language.Haskell.TH.Ppr.Ppr (Language.Haskell.TH.Context.DecStatus a)