dllist.scm

;; untested
(define-record-type end)

(define-record-type (node %node node?)
  (fields (immutable left %left)
          (immutable value value)
          (immutable right %right)))

(define-syntax-rule (node left value right)
  (%node (delay left) value (delay right)))

(define left (compose force %left))
(define right (compose force %right))

(define (list->dllist list)
  (define (next list prev)
    (if (null? list)
        (make-end)
        (letrec ((this (node prev (car list) (next (cdr list) this))))
          this)))
  (next list (make-end)))