thread State thru to backends

Types.hs

@@ -1,14 +1,35 @@
 {- git-annex core data types -}
 
 module Types (
-	State(..)
+	State(..),
+	Key(..),
+	Backend(..)
 ) where
 
-import BackendType
 import GitRepo
 
 -- git-annex's runtime state
 data State = State {
 	repo :: GitRepo,
 	backends :: [Backend]
+} deriving (Show)
+
+-- annexed filenames are mapped into keys
+type Key = FilePath
+
+-- this structure represents a key/value backend
+data Backend = Backend {
+	-- name of this backend
+	name :: String,
+	-- converts a filename to a key
+	getKey :: State -> FilePath -> IO (Maybe Key),
+	-- stores a file's contents to a key
+	storeFileKey :: State -> FilePath -> Key -> IO Bool,
+	-- retrieves a key's contents to a file
+	retrieveKeyFile :: Key -> FilePath -> IO Bool,
+	-- removes a key
+	removeKey :: Key -> IO Bool
 }
+
+instance Show Backend where
+	show backend = "Backend { name =\"" ++ (name backend) ++ "\" }"