I think you'll find that class Typeable, defined in Data.Dynamic, is pretty much exactly the class you describe. It's indeed a good thing. Simon | -----Original Message----- | From: template-haskell-admin@haskell.org [mailto:template-haskell-admin@haskell.org] On Behalf Of | Andre Pang | Sent: 07 July 2003 09:55 | To: template-haskell@haskell.org | Subject: [Template-haskell] reifyType function | | Hi all, | | Sean Seefried and I managed to implement a reifyType function, which | we're calling rType since there's already that annoying built-in | reifyType identifier ;). It's defined in a ReifyType module which | looks like thus: | | --8<-- | module ReifyType | where | | import Data.Dynamic | import Language.Haskell.THSyntax | | class ReifyType a where | rType :: a -> Typ | | instance (ReifyType a, ReifyType b) => ReifyType (a, b) where | rType (_ :: (t, u)) = Tapp (Tapp (Tcon (Tuple 2)) (rType (undefined | :: t))) | (rType (undefined :: u)) | | instance ReifyType a => ReifyType [a] where | rType (_ :: [t]) = Tapp (Tcon List) (rType (undefined :: t)) | | instance Typeable a => ReifyType a where | rType (_ :: t) = (Tcon (TconName typeAsString)) | where | typeAsString = show $ typeOf (undefined :: t) | | instance (ReifyType a, ReifyType b) => ReifyType (a->b) where | rType (_ :: t -> u) | = (Tapp (rType (undefined :: t)) (rType (undefined :: u))) | --8<-- | | An example of how to use it: | | 18:48 ~/Desktop % ghci -fglasgow-exts -fallow-overlapping-instances | -fallow-undecidable-instances ReifyType.hs | Type.hs) | ... | Loading package base ... linking ... done. | Compiling ReifyType ( ReifyType.hs, interpreted ) | Ok, modules loaded: ReifyType. | *ReifyType> rType Char.toLower | Loading package haskell98 ... linking ... done. | Loading package haskell-src ... linking ... done. | Tapp (Tcon (TconName "Char")) (Tcon (TconName "Char")) | *ReifyType> rType ((+) :: (Int -> Int -> Int)) | Tapp (Tcon (TconName "Int")) (Tapp (Tcon (TconName "Int")) (Tcon | (TconName "Int"))) | *ReifyType> rType "foobar" | Tapp (Tcon List) (Tcon (TconName "Char")) | *ReifyType> | | The major restriction is that you're limited to using it on monomorphic | types (since the typeOf function only works on monomorphic types), but | otherwise, it seems to work remarkably well. | | | -- | % Andre Pang : just.your.average.bounty.hunter | | _______________________________________________ | template-haskell mailing list | template-haskell@haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell