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|
-- | An identifier is a type used to uniquely identify a resource, target...
--
-- One can think of an identifier as something similar to a file path. An
-- identifier is a path as well, with the different elements in the path
-- separated by @/@ characters. Examples of identifiers are:
--
-- * @posts/foo.markdown@
--
-- * @index@
--
-- * @error/404@
--
-- The most important difference between an 'Identifier' and a file path is that
-- the identifier for an item is not necesserily the file path.
--
-- For example, we could have an @index@ identifier, generated by Hakyll. The
-- actual file path would be @index.html@, but we identify it using @index@.
--
-- @posts/foo.markdown@ could be an identifier of an item that is rendered to
-- @posts/foo.html@. In this case, the identifier is the name of the source
-- file of the page.
--
-- An `Identifier` carries the type of the value it identifies. This basically
-- means that an @Identifier (Page String)@ refers to a page.
--
-- It is a phantom type parameter, meaning you can safely change this if you
-- know what you are doing. You can change the type using the 'castIdentifier'
-- function.
--
-- If the @a@ type is not known, Hakyll traditionally uses @Identifier ()@.
--
{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}
module Hakyll.Core.Identifier
( Identifier (..)
, castIdentifier
, parseIdentifier
, toFilePath
, setGroup
) where
import Control.Arrow (second)
import Control.Applicative ((<$>), (<*>))
import Control.Monad (mplus)
import Data.Monoid (Monoid, mempty, mappend)
import Data.List (intercalate)
import Data.Binary (Binary, get, put)
import GHC.Exts (IsString, fromString)
import Data.Typeable (Typeable)
-- | An identifier used to uniquely identify a value
--
data Identifier a = Identifier
{ identifierGroup :: Maybe String
, identifierPath :: String
} deriving (Eq, Ord, Typeable)
instance Monoid (Identifier a) where
mempty = Identifier Nothing ""
Identifier g1 p1 `mappend` Identifier g2 p2 =
Identifier (g1 `mplus` g2) (p1 `mappend` p2)
instance Binary (Identifier a) where
put (Identifier g p) = put g >> put p
get = Identifier <$> get <*> get
instance Show (Identifier a) where
show i@(Identifier Nothing _) = toFilePath i
show i@(Identifier (Just g) _) = toFilePath i ++ " (" ++ g ++ ")"
instance IsString (Identifier a) where
fromString = parseIdentifier
-- | Discard the phantom type parameter of an identifier
--
castIdentifier :: Identifier a -> Identifier b
castIdentifier (Identifier g p) = Identifier g p
{-# INLINE castIdentifier #-}
-- | Parse an identifier from a string
--
parseIdentifier :: String -> Identifier a
parseIdentifier = Identifier Nothing
. intercalate "/" . filter (not . null) . split'
where
split' [] = [[]]
split' str = let (pre, post) = second (drop 1) $ break (== '/') str
in pre : split' post
-- | Convert an identifier to a relative 'FilePath'
--
toFilePath :: Identifier a -> FilePath
toFilePath = identifierPath
-- | Set the identifier group for some identifier
--
setGroup :: Maybe String -> Identifier a -> Identifier a
setGroup g (Identifier _ p) = Identifier g p
|
