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-- | This is the module which exports @HakyllAction@.
module Text.Hakyll.HakyllAction
( HakyllAction (..)
, createHakyllAction
, createSimpleHakyllAction
, createFileHakyllAction
, chain
, runHakyllAction
, runHakyllActionIfNeeded
) where
import Control.Arrow
import Control.Category
import Control.Monad ((<=<), mplus, unless)
import Control.Monad.Reader (liftIO)
import Prelude hiding ((.), id)
import System.IO (hPutStrLn, stderr)
import Text.Hakyll.File (toDestination, isFileMoreRecent)
import Text.Hakyll.HakyllMonad
-- | Type used for rendering computations that carry along dependencies.
data HakyllAction a b = HakyllAction
{ -- | Dependencies of the @HakyllAction@.
actionDependencies :: [FilePath]
, -- | URL pointing to the result of this @HakyllAction@.
actionUrl :: Maybe (Hakyll FilePath)
, -- | The actual render function.
actionFunction :: a -> Hakyll b
}
-- | Create a @HakyllAction@ from a function.
createHakyllAction :: (a -> Hakyll b) -- ^ Function to execute.
-> HakyllAction a b
createHakyllAction f = id { actionFunction = f }
-- | Create a @HakyllAction@ from a simple @Hakyll@ value.
createSimpleHakyllAction :: Hakyll b -- ^ Hakyll value to pass on.
-> HakyllAction () b
createSimpleHakyllAction = createHakyllAction . const
-- | Create a @HakyllAction@ that operates on one file.
createFileHakyllAction :: FilePath -- ^ File to operate on.
-> Hakyll b -- ^ Value to pass on.
-> HakyllAction () b -- ^ The resulting action.
createFileHakyllAction path action = HakyllAction
{ actionDependencies = [path]
, actionUrl = Just $ return path
, actionFunction = const action
}
-- | Run a @HakyllAction@ now.
runHakyllAction :: HakyllAction () a -- ^ Render action to run.
-> Hakyll a -- ^ Result of the action.
runHakyllAction action = actionFunction action ()
-- | Run a @HakyllAction@, but only when it is out-of-date. At this point, the
-- @actionUrl@ field must be set.
runHakyllActionIfNeeded :: HakyllAction () () -- ^ Action to run.
-> Hakyll () -- ^ Empty result.
runHakyllActionIfNeeded action = do
url <- case actionUrl action of
(Just u) -> u
Nothing -> error "No url when checking dependencies."
destination <- toDestination url
valid <- isFileMoreRecent destination $ actionDependencies action
unless valid $ do liftIO $ hPutStrLn stderr $ "Rendering " ++ destination
runHakyllAction action
-- | Chain a number of @HakyllAction@ computations.
chain :: [HakyllAction a a] -- ^ Actions to chain.
-> HakyllAction a a -- ^ Resulting action.
chain [] = id
chain list@(_:_) = foldl1 (>>>) list
instance Category HakyllAction where
id = HakyllAction
{ actionDependencies = []
, actionUrl = Nothing
, actionFunction = return
}
x . y = HakyllAction
{ actionDependencies = actionDependencies x ++ actionDependencies y
, actionUrl = actionUrl x `mplus` actionUrl y
, actionFunction = actionFunction x <=< actionFunction y
}
instance Arrow HakyllAction where
arr f = id { actionFunction = return . f }
first x = x
{ actionFunction = \(y, z) -> do y' <- actionFunction x y
return (y', z)
}
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