I think this is a consequence of the rule that we never abstract over types of kind #. But I believe this should work with my branch:
type Tuple (a :: TYPE v1) (b :: TYPE v2) = (# a, b #)
The user would have to request that the synonym be used over both * and #, but the synonym should work. The need to request the special treatment might be lifted, but we'd have to think hard about where we want the generality by default and where we want simpler behavior by default.
Richard
On Dec 6, 2015, at 1:55 PM, Ömer Sinan Ağacan
In this program:
{-# LANGUAGE MagicHash, UnboxedTuples #-}
module Main where
import GHC.Prim import GHC.Types
type Tuple a b = (# a, b #)
main = do let -- x :: Tuple Int# Float# x :: (# Int#, Float# #) x = (# 1#, 0.0# #)
return ()
If I use the first type declaration for 'x' I'm getting this error message:
Expecting a lifted type, but ‘Int#’ is unlifted
Indeed, if I look at the kinds of arguments of 'Tuple':
λ:7> :k Tuple Tuple :: * -> * -> #
It's star. I was wondering why is this not 'OpenKind'(or whatever the super-kind of star and hash). Is there a problem with this? Is this a bug? Or is this simply because type synonyms are implemented before OpenKinds? _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs