;; public.scm
;; ==========

(declare (uses internal))

(module public (bar)
(import scheme internal)
(define (bar)
  (foo 21)))


;; internal.scm
;; ============

(declare (unsafe) (fixnum-arithmetic) (unit internal))
 
(module internal (foo)
(import scheme)
(define (foo x)
  (* x 2)))


;; Building…
;; =========

Either as two shared libraries or:

chicken internal.scm -emit-all-import-libraries
csc -s -J public.scm internal.c