Experimental changes for a re-write

1 files changed, 60 insertions, 0 deletions

diff --git a/src/Text/Hakyll/Resource.hs b/src/Text/Hakyll/Resource.hs
new file mode 100644
index 0000000..a8a77b2
--- /dev/null
+++ b/src/Text/Hakyll/Resource.hs
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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