required: New command, like wanted, but for required content.

Also refactored some code to reduce duplication.

Command/GroupWanted.hs

@@ -13,6 +13,7 @@ import Command
 import Logs.PreferredContent
 import Types.Messages
 import Types.Group
+import Command.Wanted (performGet, performSet)
 
 import qualified Data.Map as M
 
@@ -24,22 +25,8 @@ seek :: CommandSeek
 seek = withWords start
 
 start :: [String] -> CommandStart
-start (g:[]) = next $ performGet g
+start (g:[]) = next $ performGet groupPreferredContentMapRaw g
 start (g:expr:[]) = do
 	showStart "groupwanted" g
-	next $ performSet g expr
+	next $ performSet groupPreferredContentSet expr g
 start _ = error "Specify a group."
-
-performGet :: Group -> CommandPerform
-performGet g = do
-	Annex.setOutput QuietOutput
-	m <- groupPreferredContentMapRaw
-	liftIO $ putStrLn $ fromMaybe "" $ M.lookup g m
-	next $ return True
-
-performSet :: Group -> String -> CommandPerform
-performSet g expr = case checkPreferredContentExpression expr of
-	Just e -> error $ "Parse error: " ++ e
-	Nothing -> do
-		groupPreferredContentSet g expr
-		next $ return True