Hi,
I wonder why the following code doesn't typecheck in GHC 7.4.1:
{-# LANGUAGE GADTs,RankNTypes #-}data T a where T1 :: (forall b. b -
b) - (forall a. Int - T a)
{- Error:
Data constructor `T1' returns type `forall a. Int - T a'
instead of an instance of its parent type `T a'
In the
It really seems to me that the error message you've got explains everything
quite clear.
Отправлено с iPad
31.07.2012, в 22:59, Shayan Najd Javadipour sh.n...@gmail.com написал(а):
Hi,
I wonder why the following code doesn't typecheck in GHC 7.4.1:
{-# LANGUAGE GADTs,RankNTypes #-}
If GHC handles the explicit forall in constructor T1 in the same way as
it does for function f, we have:
data T a where T1 :: (forall b. b - b) - Int - T a
Which is totally fine! The main question is then why the foralls are
handled differently?
On Tue, Jul 31, 2012 at 9:07 PM, MigMit
On Tue, Jul 31, 2012 at 2:59 PM, Shayan Najd Javadipour
sh.n...@gmail.comwrote:
{-# LANGUAGE GADTs,RankNTypes #-}data T a where T1 :: (forall b. b - b) -
(forall a. Int - T a)
{- Error:
Data constructor `T1' returns type `forall a. Int - T a'
instead of an instance of its parent type
