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-- | Internal structure of a Target, not exported outside of the library
--
{-# LANGUAGE GeneralizedNewtypeDeriving, Rank2Types #-}
module Hakyll.Core.Target.Internal
( DependencyLookup
, TargetEnvironment (..)
, TargetM (..)
, runTarget
) where
import Control.Applicative (Applicative)
import Control.Monad.Trans (MonadIO)
import Control.Monad.Reader (ReaderT, runReaderT)
import Control.Monad.State (StateT, evalStateT)
import Hakyll.Core.Identifier
import Hakyll.Core.ResourceProvider
import Hakyll.Core.Store
import Hakyll.Core.CompiledItem
-- | A lookup with which we can get dependencies
--
type DependencyLookup = Identifier -> CompiledItem
-- | Environment for the target monad
--
data TargetEnvironment = TargetEnvironment
{ targetIdentifier :: Identifier -- ^ Identifier
, targetDependencyLookup :: DependencyLookup -- ^ Dependency lookup
, targetResourceProvider :: ResourceProvider -- ^ To get resources
, targetStore :: Store -- ^ Store for caching
}
-- | State for the target monad
--
data TargetState = TargetState
{ targetSnapshot :: Int -- ^ Snapshot ID
}
-- | Monad for targets. In this monad, the user can compose targets and describe
-- how they should be created.
--
newtype TargetM a = TargetM
{ unTargetM :: ReaderT TargetEnvironment (StateT TargetState IO) a
} deriving (Monad, Functor, Applicative, MonadIO)
-- | Run a target, yielding an actual result.
--
runTarget :: TargetM a
-> Identifier
-> DependencyLookup
-> ResourceProvider
-> Store
-> IO a
runTarget target id' lookup' provider store =
evalStateT (runReaderT (unTargetM target) env) state
where
env = TargetEnvironment
{ targetIdentifier = id'
, targetDependencyLookup = lookup'
, targetResourceProvider = provider
, targetStore = store
}
state = TargetState
{ targetSnapshot = 0
}
|
