anchor.diff:             (cffi:with-foreign-string (,foreign-string ,str)
                ,@body)))))
   
  +(defmacro with-foreign-strings (bindings &body body)
  +  `(with-foreign-string ,(car bindings)
  +    ,@(if (cdr bindings)
  +          `((with-foreign-strings ,(cdr bindings) ,@body))
  +          body)))
  +
   ;; This function returns a form? Where is this used in user-code?
   (defun foreign-string-length (foreign-string)
     (declare (ignore foreign-string))
  
positive.code:    #:convert-to-foreign-string
     #:allocate-foreign-string
     #:with-foreign-string
     #:foreign-string-length              ; not implemented
     
     ;; function call
  
negative.code: (defun convert-from-foreign-usb8 (s len)
    (let ((a (make-array len :element-type '(unsigned-byte 8))))
      (dotimes (i len a)
        (setf (aref a i) (cffi:mem-ref s :unsigned-char i)))))
  