git.iko.soy/hakyll
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hakyll/src/Hakyll/Core/Metadata.hs
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1--------------------------------------------------------------------------------
2module Hakyll.Core.Metadata
3 ( Metadata
4 , MonadMetadata (..)
5 , getMetadataField
6 , getMetadataField'
7 , makePatternDependency
8 ) where
11--------------------------------------------------------------------------------
12import Control.Monad (forM)
13import Data.Map (Map)
14import qualified Data.Map as M
17--------------------------------------------------------------------------------
18import Hakyll.Core.Dependencies
19import Hakyll.Core.Identifier
20import Hakyll.Core.Identifier.Pattern
23--------------------------------------------------------------------------------
24type Metadata = Map String String
27--------------------------------------------------------------------------------
28class Monad m => MonadMetadata m where
29 getMetadata :: Identifier -> m Metadata
30 getMatches :: Pattern -> m [Identifier]
32 getAllMetadata :: Pattern -> m [(Identifier, Metadata)]
33 getAllMetadata pattern = do
34 matches' <- getMatches pattern
35 forM matches' $ \id' -> do
36 metadata <- getMetadata id'
37 return (id', metadata)
40--------------------------------------------------------------------------------
41getMetadataField :: MonadMetadata m => Identifier -> String -> m (Maybe String)
42getMetadataField identifier key = do
43 metadata <- getMetadata identifier
44 return $ M.lookup key metadata
47--------------------------------------------------------------------------------
48-- | Version of 'getMetadataField' which throws an error if the field does not
49-- exist.
50getMetadataField' :: MonadMetadata m => Identifier -> String -> m String
51getMetadataField' identifier key = do
52 field <- getMetadataField identifier key
53 case field of
54 Just v -> return v
55 Nothing -> fail $ "Hakyll.Core.Metadata.getMetadataField': " ++
56 "Item " ++ show identifier ++ " has no metadata field " ++ show key
59--------------------------------------------------------------------------------
60makePatternDependency :: MonadMetadata m => Pattern -> m Dependency
61makePatternDependency pattern = do
62 matches' <- getMatches pattern
63 return $ PatternDependency pattern matches'