Implementing this proposal in GHC, as opposed to the library-only approach, would allow for generation of much more useful and user friendly error messages. I believe this aspect is important when it comes to type systems supporting physical units. Cheers, George

This sounds pretty cool and useful. How much of this can be implemented in a library and how much of this would need to be supported on a compiler level? Ideally, most of this would be solved on the library level.