cpp superior to ghc . . .

Why does the Haskell language not allow "type" declarations to appear in the declaration parts of where and let clauses? I've just been writing a huge functions which requires lots and lots of repetitive internal type annotations (to disambiguate some complicated overloading) but I can't abbreviate them with "type" because they depend on things only in scope inside the function. In the end I abbreviated them with a few #define's but I don't really think it should be that way . . .