Can't get outside bindings in the string expression with eval-string

[Nala Ginrut]

hi guys, I want to get a variable bidden from outside environment, such as the code below: 

-----------------------correct code------------------------

(define fp (open-output-file "/tmp/aaa"))

(eval-string "(write 123 fp)" (current-module))

-------------------------end----------------------------------

This code can run successfully.

But I want to use this trick in a procedure:

-----------------------wrong code------------------------------

(define (func)

   (let ((fp (open-output-file "/tmp/aaa")))

       (eval-string "(write 123 fp)" (current-module))

    ))

-----------------------end code------------------------------------

Guile will throw :

========================================

scheme@(guile-user)> (func)

ERROR: In procedure memoize-variable-access!:

ERROR: Unbound variable: fp0

========================================

Is this a bug? Or I missed something?