Hi Norman, Try removing the parentheses; they are all redundant but GHC might be a bit too strict about them. Li-yao On 7/5/19 9:34 AM, Norman Ramsey wrote:
Here is a legacy file that does not compile with GHC 8.0.1:
{-# LANGUAGE RankNTypes, GADTs, KindSignatures #-}
module Bookgadt where
data TExp :: * -> * where TLit :: (forall a . (a -> (TExp a))) TLit' :: (a -> (TExp a))
The compiler rejects value constructor TLit with this error message:
• Data constructor ‘TLit’ returns type ‘forall a. a -> TExp a’ instead of an instance of its parent type ‘TExp a’
I really want to keep the explicit "forall," as I'm trying to make a point for readers not familiar with Haskell. Does anyone know if there is some option or other incantation that would enable this code to compile?
Norman _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.