#8178: Need TypeRep for Symbol and numeric type literals; and Typeable instances ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Nicolas Trangez points out that we don't have a `TypeRep` for types involving literal strings or numerics. E.g. what is `(typeRep (undefined :: Proxy "foo"))`? Here is Nicolas's example: {{{ {-# LANGUAGE DataKinds, KindSignatures, DeriveFunctor, DeriveDataTypeable #-} module Main where import Data.Typeable import GHC.TypeLits data NoSymbol n a b = NoSymbol a b deriving (Typeable) data WithSymbol (n :: Symbol) a b = WithSymbol a b deriving (Typeable) data Sym deriving (Typeable) main :: IO () main = do print $ typeOf (undefined :: NoSymbol Sym Int Int) let d = undefined :: WithSymbol "sym" Int Int {- print $ typeOf d No instance for (Typeable Symbol "sym") arising from a use of ‛typeOf’ -} return () }}} Just as types contain literal strings and natural numbers, so too must `TypeRep`, in some way. Once we have a suitable `TypeRep` we can make built-in instance for `Typeable` that return the appropriate representation. At the moment we have (in `Data.Typeable.Internals`): {{{ data TypeRep = TypeRep {-# UNPACK #-} !Fingerprint TyCon [TypeRep] data TyCon = TyCon { tyConHash :: {-# UNPACK #-} !Fingerprint, tyConPackage :: String, tyConModule :: String, tyConName :: String } }}} with instances for Eq and Ord. Perhaps we need {{{ data TypeRep = TcApp {-# UNPACK #-} !Fingerprint TyCon [TypeRep] | TcSym String | TcNat Integer }}} or something like that? I'm not certain. I think Iavor is going to think about it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8178 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler