Ian, Mmm...
* Allow "type Id =" (I prefer this to "type Id" as I think we are more likely to want to use the latter syntax for something else later on).
Looks kind of funny; I'm not too thrilled.
* Implementations should eta-reduce all type synonyms as much as possible, e.g. type T a b c d = X a b Int c d is equivalent to type T a b = X a b Int and type Id a = a is equivalent to a type that cannot be expressed directly.
I like this alternatie a bit better, but I can also see how it introduces a lot of potential confusing, especially for novice Haskell programmers. You write something and the compiler goes along with something else... Maybe this will serve as a source of inspiration: http:// portal.acm.org/citation.cfm?doid=581478.581496 [1]. Cheers, Stefan [1] Matthias Neubauer and Peter Thiemann. Type classes with more higher-order poly- morphism. In Proceedings of the Seventh ACM SIGPLAN International Conference on Functional Programming (ICFP ’02), Pittsburgh, Pennsylvania, USA, October 4–-6, 2002, pages 179–-190. ACM Press, 2002.