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|
-- | A Compiler manages targets and dependencies between targets.
--
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Hakyll.Core.Compiler
( Dependencies
, CompilerM
, Compiler
, runCompiler
, require
, target
) where
import Control.Arrow (second)
import Control.Applicative (Applicative, (<$>))
import Control.Monad.State (State, modify, runState)
import Control.Monad.Reader (ReaderT, ask, runReaderT)
import Data.Set (Set)
import qualified Data.Set as S
import Hakyll.Core.Identifier
import Hakyll.Core.Target.Internal
-- | A set of dependencies
--
type Dependencies = Set Identifier
-- | Add one dependency
--
addDependency :: Identifier -> CompilerM a ()
addDependency dependency = CompilerM $ modify $ addDependency'
where
addDependency' x = x
{ compilerDependencies = S.insert dependency $ compilerDependencies x
}
-- | Environment in which a compiler runs
--
data CompilerEnvironment a = CompilerEnvironment
{ compilerIdentifier :: Identifier -- ^ Target identifier
}
-- | State carried along by a compiler
--
data CompilerState = CompilerState
{ compilerDependencies :: Dependencies
}
-- | The compiler monad
--
newtype CompilerM a b = CompilerM
{ unCompilerM :: ReaderT (CompilerEnvironment a) (State CompilerState) b
} deriving (Monad, Functor, Applicative)
-- | Simplified type for a compiler generating a target (which covers most
-- cases)
--
type Compiler a = CompilerM a (TargetM a a)
-- | Run a compiler, yielding the resulting target and it's dependencies
--
runCompiler :: Compiler a -> Identifier -> (TargetM a a, Dependencies)
runCompiler compiler identifier = second compilerDependencies $
runState (runReaderT (unCompilerM compiler) env) state
where
env = CompilerEnvironment {compilerIdentifier = identifier}
state = CompilerState S.empty
-- | Require another target. Using this function ensures automatic handling of
-- dependencies
--
require :: Identifier
-> Compiler a
require identifier = do
addDependency identifier
return $ TargetM $ flip targetDependencyLookup identifier <$> ask
-- | Construct a target inside a compiler
--
target :: TargetM a a -> Compiler a
target = return
|
