Re: Newtype wrappers

On Mon, Jan 14, 2013 at 3:11 PM, Johan Tibell wrote:

On Mon, Jan 14, 2013 at 2:57 PM, Roman Cheplyaka wrote:

...

It's described here: http://hackage.haskell.org/trac/ghc/wiki/NewtypeWrappers

We seem to be talking past each other. There's a specific problem related to type classes and invariants on data types mentioned earlier on this thread. Simon's solution here seems to be that we only coerce a structure from one newtype to the base type if the constructors are exposed, hence my question if the code changes semantics due to adding imports.

I assume it would change from "doesn't compile" to "works" if you add the required import. It's the same as the FFI thing, right? If you don't import M (T(..)), then 'foreign ... :: T -> IO ()' gives an error, but import it and coerces T to its underlying type (hopefully that's a C type).