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|
-- | This module provides a monadic DSL in which the user can specify the
-- different rules used to run the compilers
--
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Hakyll.Core.Rules
( CompileRule (..)
, RuleSet (..)
, RulesM
, Rules
, runRules
, compile
, create
, route
, addCompilers
) where
import Control.Applicative (Applicative, (<$>))
import Control.Monad.Writer
import Control.Monad.Reader
import Control.Arrow (second, (>>>), arr, (>>^))
import Data.Typeable (Typeable)
import Data.Binary (Binary)
import Hakyll.Core.ResourceProvider
import Hakyll.Core.Identifier
import Hakyll.Core.Identifier.Pattern
import Hakyll.Core.Compiler.Internal
import Hakyll.Core.Route
import Hakyll.Core.CompiledItem
import Hakyll.Core.Writable
-- | Output of a compiler rule
--
-- * The compiler will produce a simple item. This is the most common case.
--
-- * The compiler will produce more compilers. These new compilers need to be
-- added to the runtime if possible, since other items might depend upon them.
--
data CompileRule = CompileRule CompiledItem
| MetaCompileRule [(Identifier, Compiler () CompileRule)]
-- | A collection of rules for the compilation process
--
data RuleSet = RuleSet
{ rulesRoute :: Route
, rulesCompilers :: [(Identifier, Compiler () CompileRule)]
}
instance Monoid RuleSet where
mempty = RuleSet mempty mempty
mappend (RuleSet r1 c1) (RuleSet r2 c2) =
RuleSet (mappend r1 r2) (mappend c1 c2)
-- | The monad used to compose rules
--
newtype RulesM a = RulesM
{ unRulesM :: ReaderT ResourceProvider (Writer RuleSet) a
} deriving (Monad, Functor, Applicative)
-- | Simplification of the RulesM type; usually, it will not return any
-- result.
--
type Rules = RulesM ()
-- | Run a Rules monad, resulting in a 'RuleSet'
--
runRules :: Rules -> ResourceProvider -> RuleSet
runRules rules provider = execWriter $ runReaderT (unRulesM rules) provider
-- | Add a route
--
tellRoute :: Route -> Rules
tellRoute route' = RulesM $ tell $ RuleSet route' mempty
-- | Add a number of compilers
--
tellCompilers :: (Binary a, Typeable a, Writable a)
=> [(Identifier, Compiler () a)]
-> Rules
tellCompilers compilers = RulesM $ tell $ RuleSet mempty $
map (second boxCompiler) compilers
where
boxCompiler = (>>> arr compiledItem >>> arr CompileRule)
-- | Add a compilation rule
--
-- This instructs all resources matching the given pattern to be compiled using
-- the given compiler
--
compile :: (Binary a, Typeable a, Writable a)
=> Pattern -> Compiler () a -> Rules
compile pattern compiler = RulesM $ do
identifiers <- matches pattern . resourceList <$> ask
unRulesM $ tellCompilers $ zip identifiers (repeat compiler)
-- | Add a compilation rule
--
-- This sets a compiler for the given identifier
--
create :: (Binary a, Typeable a, Writable a)
=> Identifier -> Compiler () a -> Rules
create identifier compiler = tellCompilers [(identifier, compiler)]
-- | Add a route
--
route :: Pattern -> Route -> Rules
route pattern route' = tellRoute $ ifMatch pattern route'
-- | Add a compiler that produces other compilers over time
--
addCompilers :: (Binary a, Typeable a, Writable a)
=> Identifier
-- ^ Identifier for this compiler
-> Compiler () [(Identifier, Compiler () a)]
-- ^ Compiler generating the other compilers
-> Rules
-- ^ Resulting rules
addCompilers identifier compiler = RulesM $ tell $ RuleSet mempty $
[(identifier, compiler >>^ makeRule)]
where
makeRule = MetaCompileRule . map (second (>>^ CompileRule . compiledItem))
|
