I have another related question: What about allowing primitive types in newtypes? λ:4> newtype Blah1 = Blah1 Int λ:5> newtype Blah2 = Blah2 Int# <interactive>:5:23: error: • Expecting a lifted type, but ‘Int#’ is unlifted • In the type ‘Int#’ In the definition of data constructor ‘Blah2’ In the newtype declaration for ‘Blah2’ Ideally second definition should be OK, and kind of Blah2 should be #. Is this too hard to do? 2015-12-16 17:22 GMT-05:00 Richard Eisenberg <eir@cis.upenn.edu>:
On Dec 16, 2015, at 2:06 PM, Ömer Sinan Ağacan <omeragacan@gmail.com> wrote:
In any case, this is not that big deal. When I read the code I thought this should be a trivial change but apparently it's not.
No, it's not. Your example (`f :: (Int#, b) -> b`) still has an unboxed thing in a boxed tuple. Boxed tuples simply can't (currently) hold unboxed things. And changing that is far from trivial. It's not the polymorphism that's the problem -- it's the unboxed thing in a boxed tuple.
Richard