Generalize mkResultT to arbitrary showable failures

A lot of Ganeti function return a type IO (GenericResult e a)
with various failure types e. It is often necessary to combine
all those results in a generic ResultT String IO a
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

src/Ganeti/BasicTypes.hs

@@ -42,6 +42,7 @@ module Ganeti.BasicTypes
   , Result
   , ResultT(..)
   , mkResultT
+  , mkResultT'
   , withError
   , withErrorT
   , toError
@@ -292,6 +293,11 @@ tryError = flip catchError (return . Left) . liftM Right
 mkResultT :: (Monad m, Error e) => m (Result a) -> ResultT e m a
 mkResultT = ResultT . liftM toErrorStr
 
+-- | Generalisation of mkResultT accepting any showable failures.
+mkResultT' :: (Monad m, Error e, Show s)
+           => m (GenericResult s a) -> ResultT e m a
+mkResultT' = mkResultT . liftM (genericResult (Bad . show) Ok)
+
 -- | Simple checker for whether a 'GenericResult' is OK.
 isOk :: GenericResult a b -> Bool
 isOk (Ok _) = True