(define-module (simple-sealers)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:export (make-sealer-triplet))

;; Make a sealer, unsealer, and brand-check predicate using
;; dynamic type generation.
(define (make-sealer-triplet)
  (define-record-type <seal>
    (seal val)      ; constructor (sealer)
    sealed?         ; predicate   (brand-check)
    (val unseal))   ; accessor    (unsealer)

  ;; Prevents snooping on contents at REPL, etc
  (define (print-seal _rec port)
    (display "#<sealed>" port))
  (set-record-type-printer! <seal> print-seal)

  ;; Return sealer, unsealer, sealed? predicate
  (values seal unseal sealed?))