After finalizing some of my idea prototypes in Ωmega, I intend to port a part of the code to Haskell, to enjoy the speed advantages of a compiled language.
Unfortunately Haskell does not support user-defined kinds, so I was wondering how to simulate them at least, in order to get some confidence that my type-level constructs do not drift into no-no-land.
This literate haskell file demonstrates how I put instance constraints to work, and thereby define the inference rules for well-kinded phantom type indexes. I am sure somebody has already done this, I would like to hear about it. Anyway, this almost allows me to introduce Ωmega's checked singleton types in Haskell.
Sadly GHC does not yet allow instance definitions for type families, but it would be cool if somebody could provide me a workaround.