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authorJoey Hess2015-01-25 15:16:58 -0400
committerJoey Hess2015-01-25 15:16:58 -0400
commit401b857eef13ca7d3f7b8f6b88e9237884fcd906 (patch)
treeeb4b5c189349b5a86b3b39edbe039956d3a1a3b8 /src/Propellor/Types/Val.hs
parent1df70ba81ddfbd4ceeb5344793f7714a35706c8f (diff)
parentcdd88b080af534231aae8a64ef327f0597a5b5b3 (diff)
Merge branch 'joeyconfig'
Conflicts: doc/todo/info_propigation_out_of_nested_properties.mdwn privdata.joey/privdata.gpg
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diff --git a/src/Propellor/Types/Val.hs b/src/Propellor/Types/Val.hs
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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