GADTs: malformed constructor signature

Rather unituitively, GHC allows

> {-# OPTIONS -fglasgow-exts #-}
> > data T :: * where 
>   C :: Int -> Int -> T

but not

> data T :: * where 
>   C :: Int -> (Int -> T)

Sometimes, I like to parenthesize the result type for emphasis.

Cheers, Ralf