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-- | A resource represents data for a website
--
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Text.Hakyll.Resource
( Metadata (..)
, Resource (..)
, getData
, getMetadata
, getMetadataList
) where
import Data.Monoid (Monoid, mempty, mappend)
import Control.Applicative (Applicative, (<*>), pure)
-- | Metadata for a resource
--
newtype Metadata = Metadata {unMetadata :: [(String, String)]}
deriving (Show, Eq, Ord, Monoid)
-- | A resource represents a data source for the website. It contains a value
-- and a number of metadata fields
--
data Resource a = Resource
{ resourceMetadata :: Metadata
, resourceData :: a
} deriving (Show, Eq, Ord)
instance Functor Resource where
fmap f (Resource m d) = Resource m $ f d
instance Applicative Resource where
pure d = Resource mempty d
(Resource m1 f) <*> (Resource m2 d) = Resource (mappend m2 m1) (f d)
instance Monad Resource where
return d = Resource mempty d
(Resource m1 d) >>= f = let Resource m2 d' = f d
in Resource (mappend m2 m1) d'
instance Monoid a => Monoid (Resource a) where
mempty = Resource mempty mempty
mappend (Resource m1 d1) (Resource m2 d2) =
Resource (mappend m1 m2) (mappend d1 d2)
-- | Get the data from a resource
--
getData :: Resource a -> a
getData = resourceData
-- | Get a metadata field from a resource
--
getMetadata :: String -> Resource a -> Maybe String
getMetadata k (Resource m _) = lookup k $ unMetadata m
-- | Get a metadata field from a resource. If multiple fields with the same name
-- exist, they will all be returned
--
getMetadataList :: String -> Resource a -> [String]
getMetadataList k = map snd . filter ((== k) . fst)
. unMetadata . resourceMetadata
|
