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diff --git a/Command.hs b/Command.hs
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+{- git-annex command types
+ -
+ - Copyright 2010 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Command where
+
+import Types
+import Backend
+
+{- A subcommand runs in four stages.
+ -
+ - 0. The seek stage takes the parameters passed to the subcommand,
+ -    looks through the repo to find the ones that are relevant
+ -    to that subcommand (ie, new files to add), and generates
+ -    a list of start stage actions. -}
+type SubCmdSeek = [String] -> Annex [SubCmdStart]
+{- 1. The start stage is run before anything is printed about the
+  -   subcommand, is passed some input, and can early abort it
+  -   if the input does not make sense. It should run quickly and
+  -   should not modify Annex state. -}
+type SubCmdStart = Annex (Maybe SubCmdPerform)
+{- 2. The perform stage is run after a message is printed about the subcommand
+ -    being run, and it should be where the bulk of the work happens. -}
+type SubCmdPerform = Annex (Maybe SubCmdCleanup)
+{- 3. The cleanup stage is run only if the perform stage succeeds, and it
+ -    returns the overall success/fail of the subcommand. -}
+type SubCmdCleanup = Annex Bool
+{- Some helper functions are used to build up SubCmdSeek and SubCmdStart
+ - functions. -}
+type SubCmdSeekStrings = SubCmdStartString -> SubCmdSeek
+type SubCmdStartString = String -> SubCmdStart
+type SubCmdSeekBackendFiles = SubCmdStartBackendFile -> SubCmdSeek
+type SubCmdStartBackendFile = (FilePath, Maybe Backend) -> SubCmdStart
+
+notAnnexed :: FilePath -> Annex (Maybe a) -> Annex (Maybe a)
+notAnnexed file a = do
+	r <- Backend.lookupFile file
+	case (r) of
+		Just _ -> return Nothing
+		Nothing -> a
+
+isAnnexed :: FilePath -> ((Key, Backend) -> Annex (Maybe a)) -> Annex (Maybe a)
+isAnnexed file a = do
+	r <- Backend.lookupFile file
+	case (r) of
+		Just v -> a v
+		Nothing -> return Nothing