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typesetting/xenomorph/xenomorph/private/optional.rkt

29 lines
706 B
Racket

#lang racket/base
(require "racket.rkt")
(provide (all-defined-out))
#|
approximates
https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
|#
(define-subclass xenomorph-base% (Optional type [condition #t])
(define (resolve-condition parent)
(if (procedure? condition)
(condition parent)
condition))
(define/augment (decode stream parent)
(when (resolve-condition parent)
(send type decode stream parent)))
(define/augment (size val parent)
(when (resolve-condition parent)
(send type size val parent)))
(define/augment (encode stream val parent)
(when (resolve-condition parent)
(send type encode stream val parent))))