[racket] macros in local namespaces?...

Hi there,

I'm trying to get a grip on macros. Here is a very simple Racket  
expression  (1):

(letrec [(a 2)
          (b 3)
          (afn (lambda (x) (+ x a)))
          (bfn (lambda (x) (+ x b)))]
    (afn (bfn 2)))

Now I need a syntactic abstraction for afn and bfn. The following will  
do in first approximation (2):

(define-syntax-rule (absfn varname) (lambda (x) (+ x varname)))

(letrec [(a 2)
          (b 3)
          (afn (absfn a))
          (bfn (absfn b))]
    (afn (bfn 2)))


However, it will fail due to scoping rules in the following example (3):

(define-syntax-rule (absfn varname) (lambda (x) (+ (+ x localc) varname)))

(letrec [(a 2)
          (b 3)
          (localc 4)
          (afn (absfn a))
          (bfn (absfn b))]
    (afn (bfn 2)))

In other words, my syntactic extension absfn needs to be embedded in  
the namespace of the sorrounding expression (or as a "dumb" macro  
which simply does lexical replacement without considering scoping, but  
needless to say such a macro would be unhygienic).
I suspect that letrec-syntax was meant for that purpose, but I can't  
figure out how the parameters to define-syntax-rule would translate to  
those of letrec-syntax.

Does anyone have sample code for how to get (3) above to work?

Thanks!