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+module Propellor.Types.Val where
+
+import Data.Monoid
+
+import Propellor.Types.Empty
+
+data Val a = Val a | NoVal
+ deriving (Eq, Show)
+
+instance Monoid (Val a) where
+ mempty = NoVal
+ mappend old new = case new of
+ NoVal -> old
+ _ -> new
+
+instance Empty (Val a) where
+ isEmpty NoVal = True
+ isEmpty _ = False
+
+fromVal :: Val a -> Maybe a
+fromVal (Val a) = Just a
+fromVal NoVal = Nothing