ref.scm

(define ~/default
  (case-lambda
   ((obj index default)
    (ref obj index default))
   ((obj index i x . xs)
    (apply ~/default
           (ref obj index)
           i x xs))))

(define-syntax ~~
  (syntax-rules ()
    ((_ args ...)
     (letrec ((recur
               (case-lambda
                ((obj index args ...)
                 (ref obj index args ...))
                ((obj index args ... x . xs)
                 (apply recur
                        (ref obj index)
                        args ... x
                        xs)))))
       recur))))

;; gosh> (define ht (make-hash-table))
;; ht
;; gosh> ((~~ default) ht 'foo 'bar)
;; bar