[Haskell-cafe] TypeLits & Typeable

24 Aug 2013

      Hello Cafe,

I was playing around with TypeLits in combination with Typeable (using
GHC 7.7.7.20130812 FWIW), but was surprised to find Symbols aren't
Typeable, and as such the following doesn't work. Is this intentional,
or am I missing something?

Thanks,

Nicolas

{-# 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 ()

[Haskell-cafe] TypeLits & Typeable

Nicolas Trangez