1 files changed, 33 insertions, 5 deletions
diff --git a/Propellor/Property.hs b/Propellor/Property.hs
index 3a3c1cb1..5b1800ef 100644
--- a/Propellor/Property.hs
+++ b/Propellor/Property.hs
@@ -10,8 +10,10 @@ import "mtl" Control.Monad.Reader
 
 import Propellor.Types
 import Propellor.Types.Attr
+import Propellor.Attr
 import Propellor.Engine
 import Utility.Monad
+import System.FilePath
 
 makeChange :: IO () -> Propellor Result
 makeChange a = liftIO a >> return MadeChange
@@ -52,14 +54,19 @@ p1 `before` p2 = Property (propertyDesc p1) $ do
 -- file to indicate whether it has run before.
 -- Use with caution.
 flagFile :: Property -> FilePath -> Property
-flagFile property flagfile = Property (propertyDesc property) $
-	go =<< liftIO (doesFileExist flagfile)
+flagFile property = flagFile' property . return
+
+flagFile' :: Property -> IO FilePath -> Property
+flagFile' property getflagfile = Property (propertyDesc property) $ do
+	flagfile <- liftIO getflagfile
+	go flagfile =<< liftIO (doesFileExist flagfile)
   where
-	go True = return NoChange
-	go False = do
+	go _ True = return NoChange
+	go flagfile False = do
 		r <- ensureProperty property
 		when (r == MadeChange) $ liftIO $ 
-			unlessM (doesFileExist flagfile) $
+			unlessM (doesFileExist flagfile) $ do
+				createDirectoryIfMissing True (takeDirectory flagfile)
 				writeFile flagfile ""
 		return r
 
@@ -85,6 +92,26 @@ check c property = Property (propertyDesc property) $ ifM (liftIO c)
 	, return NoChange
 	)
 
+-- | Marks a Property as trivial. It can only return FailedChange or
+-- NoChange. 
+--
+-- Useful when it's just as expensive to check if a change needs
+-- to be made as it is to just idempotently assure the property is
+-- satisfied. For example, chmodding a file.
+trivial :: Property -> Property
+trivial p = Property (propertyDesc p) $ do
+	r <- ensureProperty p
+	if r == MadeChange
+		then return NoChange
+		else return r
+
+-- | Makes a property that is satisfied differently depending on the host's
+-- operating system. 
+--
+-- Note that the operating system may not be declared for some hosts.
+withOS :: Desc -> (Maybe System -> Propellor Result) -> Property
+withOS desc a = Property desc $ a =<< getOS
+
 boolProperty :: Desc -> IO Bool -> Property
 boolProperty desc a = Property desc $ ifM (liftIO a)
 	( return MadeChange
@@ -105,6 +132,7 @@ host :: HostName -> Host
 host hn = Host [] (\_ -> newAttr hn)
 
 -- | Adds a property to a Host
+--
 -- Can add Properties, RevertableProperties, and AttrProperties
 (&) :: IsProp p => Host -> p -> Host
 (Host ps as) & p = Host (ps ++ [toProp p]) (getAttr p . as)