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-- | Internal structure of a Target, not exported outside of the library
--
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Hakyll.Core.Target.Internal
( DependencyLookup
, TargetEnvironment (..)
, TargetM (..)
, Target
, runTarget
) where
import Control.Applicative (Applicative)
import Control.Monad.Trans (MonadIO)
import Control.Monad.Reader (ReaderT, runReaderT)
import Hakyll.Core.Identifier
import Hakyll.Core.ResourceProvider
-- | A lookup with which we can get dependencies
--
type DependencyLookup a = Identifier -> a
-- | Environment for the target monad
--
data TargetEnvironment a = TargetEnvironment
{ targetIdentifier :: Identifier -- ^ Identifier
, targetDependencyLookup :: DependencyLookup a -- ^ Dependency lookup
, targetResourceProvider :: ResourceProvider -- ^ To get resources
}
-- | Monad for targets. In this monad, the user can compose targets and describe
-- how they should be created.
--
newtype TargetM a b = TargetM {unTargetM :: ReaderT (TargetEnvironment a) IO b}
deriving (Monad, Functor, Applicative, MonadIO)
-- | Simplification of the 'TargetM' type for concrete cases: the type of the
-- returned item should equal the type of the dependencies.
--
type Target a = TargetM a a
-- | Run a target, yielding an actual result.
--
runTarget :: Target a
-> Identifier
-> DependencyLookup a
-> ResourceProvider
-> IO a
runTarget target id' lookup' provider = runReaderT (unTargetM target) env
where
env = TargetEnvironment
{ targetIdentifier = id'
, targetDependencyLookup = lookup'
, targetResourceProvider = provider
}
|
