112 lines
4 KiB
Haskell
112 lines
4 KiB
Haskell
--------------------------------------------------------------------------------
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-- | An identifier is a type used to uniquely identify a resource, target...
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--
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-- One can think of an identifier as something similar to a file path. An
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-- identifier is a path as well, with the different elements in the path
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-- separated by @/@ characters. Examples of identifiers are:
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--
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-- * @posts/foo.markdown@
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--
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-- * @index@
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--
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-- * @error/404@
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--
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-- The most important difference between an 'Identifier' and a file path is that
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-- the identifier for an item is not necesserily the file path.
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--
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-- For example, we could have an @index@ identifier, generated by Hakyll. The
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-- actual file path would be @index.html@, but we identify it using @index@.
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--
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-- @posts/foo.markdown@ could be an identifier of an item that is rendered to
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-- @posts/foo.html@. In this case, the identifier is the name of the source
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-- file of the page.
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--
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-- An `Identifier` carries the type of the value it identifies. This basically
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-- means that an @Identifier (Page String)@ refers to a page.
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--
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-- It is a phantom type parameter, meaning you can safely change this if you
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-- know what you are doing. You can change the type using the 'castIdentifier'
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-- function.
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--
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-- If the @a@ type is not known, Hakyll traditionally uses @Identifier ()@.
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{-# LANGUAGE DeriveDataTypeable #-}
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
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module Hakyll.Core.Identifier
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( Identifier
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, fromFilePath
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, toFilePath
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, castIdentifier
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, identifierVersion
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, setVersion
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) where
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--------------------------------------------------------------------------------
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import Control.Applicative ((<$>), (<*>))
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import Control.DeepSeq (NFData (..))
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import Data.List (intercalate)
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import System.FilePath (dropTrailingPathSeparator, splitPath)
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--------------------------------------------------------------------------------
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import Data.Binary (Binary (..))
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import Data.Typeable (Typeable)
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import GHC.Exts (IsString, fromString)
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--------------------------------------------------------------------------------
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-- | An identifier used to uniquely identify a value
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data Identifier a = Identifier
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{ identifierVersion :: Maybe String
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, identifierPath :: String
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} deriving (Eq, Ord, Typeable)
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--------------------------------------------------------------------------------
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instance Binary (Identifier a) where
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put (Identifier v p) = put v >> put p
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get = Identifier <$> get <*> get
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--------------------------------------------------------------------------------
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instance IsString (Identifier a) where
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fromString = fromFilePath
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--------------------------------------------------------------------------------
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instance NFData (Identifier a) where
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rnf (Identifier v p) = rnf v `seq` rnf p `seq` ()
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--------------------------------------------------------------------------------
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instance Show (Identifier a) where
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show i = case identifierVersion i of
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Nothing -> toFilePath i
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Just v -> toFilePath i ++ " (" ++ v ++ ")"
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--------------------------------------------------------------------------------
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-- | Parse an identifier from a string
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fromFilePath :: String -> Identifier a
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fromFilePath = Identifier Nothing .
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intercalate "/" . filter (not . null) . split'
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where
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split' = map dropTrailingPathSeparator . splitPath
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--------------------------------------------------------------------------------
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-- | Convert an identifier to a relative 'FilePath'
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toFilePath :: Identifier a -> FilePath
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toFilePath = identifierPath
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--------------------------------------------------------------------------------
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-- | Discard the phantom type parameter of an identifier
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castIdentifier :: Identifier a -> Identifier b
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castIdentifier (Identifier v p) = Identifier v p
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{-# INLINE castIdentifier #-}
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--------------------------------------------------------------------------------
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setVersion :: Maybe String -> Identifier a -> Identifier a
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setVersion v i = i {identifierVersion = v}
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