[plt-scheme] defstruct and class?

On Sat, Jul 26, 2008 at 10:39 AM, Matthias Felleisen
<matthias at ccs.neu.edu> wrote:
> Personal preference: I tend to start programming with modules that are
> class-like:
> #lang scheme
>  ;; structs for datatype Foo
>  (define-struct foo (moo bar))
>  -- functions
>  (define (f a-foo x y z) ...)
>  (define (g a-foo x) ...)
>  (define (h a-bar) ...)
> I almost always use a "with" macro that opens up instances of Foo in these
> functions.

How does that 'with' macro work? Is that something you wrote yourself
or provided with PLT?