instance Metadata SubBlock

diff --git a/Codec/Audio/WavPack/Metadata.hs b/Codec/Audio/WavPack/Metadata.hs
index edf76f25093b9afea31f71bdb2839725d73a2b79..f7dc2a0bc7ac6573ec7282382720d3475bf2dd3c 100644 (file)
--- a/Codec/Audio/WavPack/Metadata.hs
+++ b/Codec/Audio/WavPack/Metadata.hs
@@ -6,7 +6,7 @@
 -- | WavPack metadata sub-blocks
 module Codec.Audio.WavPack.Metadata
     ( Metadata(..)
-    , SubBlock(..)
+    , SubBlock
 
     , Dummy(..)
     , Unknown(..)
@@ -21,13 +21,29 @@ import qualified Data.ByteString.Lazy as L
 import Data.Typeable
 import Prelude.Unicode
 
+-- | Type class for every metadata sub-blocks.
 class (Binary α, Eq α, Show α, Typeable α) ⇒ Metadata α where
+    -- | Get the metadata ID (mandatory).
     metaID   ∷ α → Word8
+    -- | Get the size of metadata (optional).
     metaSize ∷ α → Word32
-
     metaSize = fromIntegral ∘ L.length ∘ runPut ∘ put
+    -- | Cast a 'SubBlock' to this type of metadata (optional).
+    fromSubBlock ∷ SubBlock → Maybe α
+    fromSubBlock (SubBlock a) = cast a
+    -- | Wrap the metadata into 'SubBlock' (optional).
+    toSubBlock ∷ α → SubBlock
+    toSubBlock = SubBlock
 
+-- | An opaque sub-block container.
 data SubBlock = ∀α. Metadata α ⇒ SubBlock α
+                deriving Typeable
+
+instance Metadata SubBlock where
+    metaID   (SubBlock a) = metaID a
+    metaSize (SubBlock a) = metaSize a
+    fromSubBlock = Just
+    toSubBlock   = id
 
 instance Binary SubBlock where
     put (SubBlock a)
@@ -84,7 +100,7 @@ instance Show SubBlock where
 -- | Dummy metadata to pad WavPack blocks.
 data Dummy
     = Dummy {
-        dumSize ∷ !Word32
+        dumSize ∷ Word32
       }
     deriving (Eq, Show, Typeable)
 
@@ -99,7 +115,7 @@ instance Binary Dummy where
 -- | Unknown but optional metadata found in the WavPack block.
 data Unknown
     = Unknown {
-        unkID   ∷ !Word8
+        unkID   ∷ Word8
       , unkData ∷ L.ByteString
       }
     deriving (Eq, Show, Typeable)