[plt-scheme] macro question

Sam TH wrote:

> 3 - maintainability.  When you look at a function, or a datastructure,
> you immediately know something about how it works, and when you
> perform maintenance in one place, you're prevented from screwing
> things up in other places.
> 
> For Typed Scheme, we've focused mainly on benefit 3.

How do contracts fit into this view? Are they an alternative, 
orthogonal, or do both types and contracts need further development in 
order to be used effectively in tandem? (My knowledge of type theory is 
only at about the senior undergraduate level at this point, and I 
haven't looked seriously at PLT contracts yet.) Thanks. --PR