the mapping to variables, except that the
;;; variable is dereferenced.
;;;

(define (module-symbol-local-binding m v . opt-val)
  "Return the binding of variable V specified by name within module M,
signaling an error if the variable is unbound.  If the OPT-VALUE is
passed, then instead of signaling an error, return OPT-VALUE."
  (let ((var (module-local-variable m v)))
    (if (and var (variable-bound? var))
        (variable-ref var)
        (if (not (null? opt-val))
            (car opt-val)
            (error "Locally unbound variable." v)))))

(define (module-symbol-binding m v . opt-val)
  "Return the binding of variable V specified by name within module M,
signaling an error if the variable is unbound.  If the OPT-VALUE is
passed, then instead of signaling an error, return OPT-VALUE."
  (let ((var (module-variable m v)))
    (if (and var (variable-bound? var))
        (variable-ref var)
        (if (not (null? opt-val))
            (car opt-val)
            (error "Unbound variable." v)))))