Can I use reallyUnsafePtrEquality# reliably to identify whether a value is a nullary constructor of a particular type? For example, if I have data Foo = Foo Can I write isFoo :: a -> Bool isFoo !a = isTrue# (reallyUnsafePtrEquality# a Foo) instead of isFoo :: forall a. Typeable a => a -> Bool isFoo a | Just Refl <- eqTypeRep (typeRep @a) (typeRep @Foo) , Foo <- a = True | otherwise = False The reason I'm asking is because this would let me (potentially) raiseIO# a nullary constructor and then catch# it and see if it was what I was looking for rather than having to open a SomeException to get to an Exception dictionary, open that to get a TypeRep, and then peer inside that to check a Fingerprint. That is, I'd get lighter-weight exceptions that only carry the information I actually need. Thanks, David