Hi Uri, Here's how it might look. {-# LANGUAGE DeriveDataTypeable, DataKinds, KindSignatures, ScopedTypeVariables #-} module Example where import Data.Typeable import Data.Proxy data Tag = TagV | TagE | TagA | TagL deriving Typeable class TypeableTag (t :: Tag) where tagRep :: Proxy t -> TypeRep instance TypeableTag TagV where tagRep _ = mkTyConApp (mkTyCon3 "mypkg" "Example" "'TagV") [] -- ... same for the other tags newtype TaggedVar (t :: Tag) = TaggedVar Int instance TypeableTag t => Typeable (TaggedVar t) where typeOf _ = mkTyConApp (mkTyCon3 "mkpkg" "Example" "TaggedVar") [tagRep (Proxy :: Proxy t)] Roman * Uri Braun <uribraun@eecs.harvard.edu> [2013-01-24 16:14:53-0500]

I've read the recent posting titled "Non-derivable Typeable" (http://www.mail-archive.com/haskell-cafe@haskell.org/msg103616.html) which explains that Typeable cannot be automatically derived for cases where the kind is constrained.

I'm very impressed that a solution is imminent. In the interim, can somebody kindly suggest a workaround? I'm okay with a manual instance, but I'd appreciate some help as to how to write one. I'm looking for a Typeable instance for TaggedVar for the following example below (extracted from my code).

Thank you in advance!

+Uri

{-# LANGUAGE DeriveDataTypeable, DataKinds, KindSignatures #-} module Example where

import Data.Typeable

data Tag = TagV | TagE | TagA | TagL deriving Typeable

newtype TaggedVar (t :: Tag) = TaggedVar Int

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