[plt-scheme] Eval throwing undefined identifier error

This is probably related to eval and environments. But in the  
following code why is f not available to the eval in module-b. How to  
make it work?

Thanks,

Jaime


(module a mzscheme
   (provide (all-defined))
   (define (f x) (list x x)))


(module b mzscheme
   (require "a.scm")
   (define g
     (let* ((port (open-input-string "`(,(f 1) ,(f 2))"))
            (input (eval (read port))))
       (display input))))