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I have a type class Atomic , which defines functions for converting certain types to/from a wrapper value ( Atom ). I'd like to define a QuickCheck property which states: "for all instances of Atomic , any value may be stored and retrieved safely". The property looks like this: class Atomic a where toAtom :: a -> Atom fromAtom :: Atom -> Maybe a prop_AtomIdentity x = fromAtom (toAtom x) == Just x However, if I just try to run that property through QuickCheck, it just picks one instance ( Bool ) and tests it. I'm currently working around that by defining type signatures for each supported atomic type in the test list, but this is verbose and error-prone: containerTests = [ run (prop_AtomIdentity :: Bool -> Bool) , run (prop_AtomIdentity :: Word8 -> Bool) , run (prop_AtomIdentity :: String -> Bool) {- etc -} ] I'm trying to define a function which will do this automatically: forallAtoms :: (Atomic a, Show a) => (a -> Bool) -> [TestOptions -> IO TestResult] forallAtoms x = [ run (x :: Bool -> Bool) , run (x :: Word8 -> Bool) , run (x :: String -> Bool) {- etc -} ] containerTests = forallAtoms prop_AtomIdentity But it fails with a typecheck error: Tests/Containers.hs:33:0: Couldn't match expected type `Word8' against inferred type `String' In the first argument of `run', namely `(x :: Word8 -> Bool)' In the expression: run (x :: Word8 -> Bool) In the expression: [run (x :: Bool -> Bool), run (x :: Word8 -> Bool), run (x :: String -> Bool)] Is there a better way to test a QC property against multiple types? If not, can forallAtoms be made to work or is that not supported by the type system?

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