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|
--------------------------------------------------------------------------------
module Hakyll.Core.Metadata
( Metadata
, MonadMetadata (..)
, getMetadataField
, getMetadataField'
, makePatternDependency
) where
--------------------------------------------------------------------------------
import Control.Monad (forM)
import Data.Map (Map)
import qualified Data.Map as M
import qualified Data.Set as S
--------------------------------------------------------------------------------
import Hakyll.Core.Dependencies
import Hakyll.Core.Identifier
import Hakyll.Core.Identifier.Pattern
--------------------------------------------------------------------------------
type Metadata = Map String String
--------------------------------------------------------------------------------
class Monad m => MonadMetadata m where
getMetadata :: Identifier -> m Metadata
getMatches :: Pattern -> m [Identifier]
getAllMetadata :: Pattern -> m [(Identifier, Metadata)]
getAllMetadata pattern = do
matches' <- getMatches pattern
forM matches' $ \id' -> do
metadata <- getMetadata id'
return (id', metadata)
--------------------------------------------------------------------------------
getMetadataField :: MonadMetadata m => Identifier -> String -> m (Maybe String)
getMetadataField identifier key = do
metadata <- getMetadata identifier
return $ M.lookup key metadata
--------------------------------------------------------------------------------
-- | Version of 'getMetadataField' which throws an error if the field does not
-- exist.
getMetadataField' :: MonadMetadata m => Identifier -> String -> m String
getMetadataField' identifier key = do
field <- getMetadataField identifier key
case field of
Just v -> return v
Nothing -> fail $ "Hakyll.Core.Metadata.getMetadataField': " ++
"Item " ++ show identifier ++ " has no metadata field " ++ show key
--------------------------------------------------------------------------------
makePatternDependency :: MonadMetadata m => Pattern -> m Dependency
makePatternDependency pattern = do
matches' <- getMatches pattern
return $ PatternDependency pattern (S.fromList matches')
|
