monoid

Propellor.hs

@@ -17,7 +17,7 @@
 -- > getProperties "example.com" = Just
 -- >    [ Apt.installed ["mydaemon"]
 -- >    , "/etc/mydaemon.conf" `File.containsLine` "secure=1"
--- >        `onChange` cmdProperty "service" ["mydaemon", "restart"]]
+-- >        `onChange` cmdProperty "service" ["mydaemon", "restart"]
 -- >    ]
 -- > getProperties _ = Nothing
 --
@@ -57,3 +57,4 @@ import Data.Maybe as X
 import Data.Either as X
 import Control.Applicative as X
 import Control.Monad as X
+import Data.Monoid as X

Propellor/Engine.hs

@@ -3,6 +3,7 @@ module Propellor.Engine where
 import System.Console.ANSI
 import System.Exit
 import System.IO
+import Data.Monoid
 
 import Propellor.Types
 import Utility.Exception
@@ -42,7 +43,7 @@ ensureProperties' ps = ensure ps NoChange
 				putStrLn "done"
 		setSGR []
 		hFlush stdout
-		ensure ls (combineResult r rs)
+		ensure ls (r <> rs)
 
 warningMessage :: String -> IO ()
 warningMessage s = do

Propellor/Property.hs

@@ -2,6 +2,7 @@ module Propellor.Property where
 
 import System.Directory
 import Control.Monad
+import Data.Monoid
 
 import Propellor.Types
 import Propellor.Engine
@@ -13,16 +14,15 @@ makeChange a = a >> return MadeChange
 noChange :: IO Result
 noChange = return NoChange
 
-{- | Combines a list of properties, resulting in a single property
- - that when run will run each property in the list in turn,
- - and print out the description of each as it's run. Does not stop
- - on failure; does propigate overall success/failure.
- -}
+-- | Combines a list of properties, resulting in a single property
+-- that when run will run each property in the list in turn,
+-- and print out the description of each as it's run. Does not stop
+-- on failure; does propigate overall success/failure.
 propertyList :: Desc -> [Property] -> Property
 propertyList desc ps = Property desc $ ensureProperties' ps
 
-{- | Combines a list of properties, resulting in one property that
- - ensures each in turn, stopping on failure. -}
+-- | Combines a list of properties, resulting in one property that
+-- ensures each in turn, stopping on failure.
 combineProperties :: [Property] -> Property
 combineProperties ps = Property desc $ go ps NoChange
   where
@@ -31,14 +31,14 @@ combineProperties ps = Property desc $ go ps NoChange
 		r <- ensureProperty l
 		case r of
 			FailedChange -> return FailedChange
-			_ -> go ls (combineResult r rs)
+			_ -> go ls (r <> rs)
 	desc = case ps of
 		(p:_) -> propertyDesc p
 		_ -> "(empty)"
 
-{- | Makes a perhaps non-idempotent Property be idempotent by using a flag
- - file to indicate whether it has run before.
- - Use with caution. -}
+-- | Makes a perhaps non-idempotent Property be idempotent by using a flag
+-- file to indicate whether it has run before.
+-- Use with caution.
 flagFile :: Property -> FilePath -> Property
 flagFile property flagfile = Property (propertyDesc property) $
 	go =<< doesFileExist flagfile
@@ -50,19 +50,19 @@ flagFile property flagfile = Property (propertyDesc property) $
 			writeFile flagfile ""
 		return r
 
-{- | Whenever a change has to be made for a Property, causes a hook
- - Property to also be run, but not otherwise. -}
+--- | Whenever a change has to be made for a Property, causes a hook
+-- Property to also be run, but not otherwise.
 onChange :: Property -> Property -> Property
 property `onChange` hook = Property (propertyDesc property) $ do
 	r <- ensureProperty property
 	case r of
 		MadeChange -> do
 			r' <- ensureProperty hook
-			return $ combineResult r r'
+			return $ r <> r'
 		_ -> return r
 
-{- | Indicates that the first property can only be satisfied once
- - the second is. -} 
+-- | Indicates that the first property can only be satisfied once
+-- the second is.
 requires :: Property -> Property -> Property
 x `requires` y = combineProperties [y, x] `describe` propertyDesc x
 
@@ -73,7 +73,7 @@ describe p d = p { propertyDesc = d }
 (==>) = flip describe
 infixl 1 ==>
 
-{- | Makes a Property only be performed when a test succeeds. -}
+-- | Makes a Property only be performed when a test succeeds.
 check :: IO Bool -> Property -> Property
 check c property = Property (propertyDesc property) $ ifM c
 	( ensureProperty property

Propellor/Types.hs

@@ -1,5 +1,7 @@
 module Propellor.Types where
 
+import Data.Monoid
+
 type HostName = String
 type UserName = String
 
@@ -14,9 +16,11 @@ type Desc = String
 data Result = NoChange | MadeChange | FailedChange
 	deriving (Show, Eq)
 
-combineResult :: Result -> Result -> Result
-combineResult FailedChange _ = FailedChange
-combineResult _ FailedChange = FailedChange
-combineResult MadeChange _ = MadeChange
-combineResult _ MadeChange = MadeChange
-combineResult NoChange NoChange = NoChange
+instance Monoid Result where
+	mempty = NoChange
+
+	mappend FailedChange _ = FailedChange
+	mappend _ FailedChange = FailedChange
+	mappend MadeChange _ = MadeChange
+	mappend _ MadeChange = MadeChange
+	mappend NoChange NoChange = NoChange