What i want to know is if there is already
something like this (and suggestions for improvement of course).
...
Sometimes i find myself needing to associate a constant with a type
or, more precisely, with a type class instance.
I'm not sure if this is what you're looking for, but it seems related.
Oleg Kiselyov, Chung-chieh Shan. "Functional pearl: Implicit configurations-or, type classes reflect the values of types," in Haskell 2004. ACM, 2004, pp. 33-44. http://www.citeulike.org/user/spl/article/313800