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#lang racket/base
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(require "helper.rkt")
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/restructure/blob/master/src/Optional.coffee
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|#
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(define (resolve-condition xo parent)
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(define maybe-proc (xoptional-condition xo))
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(if (procedure? maybe-proc)
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(maybe-proc parent)
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maybe-proc))
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(define (xoptional-decode xo [port-arg (current-input-port)] #:parent [parent #f])
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(define port (->input-port port-arg))
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(parameterize ([current-input-port port])
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(when (resolve-condition xo parent)
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(decode (xoptional-type xo) #:parent parent))))
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(define (xoptional-encode xo val [port-arg (current-output-port)] #:parent [parent #f])
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(define port (if (output-port? port-arg) port-arg (open-output-bytes)))
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(parameterize ([current-output-port port])
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(when (resolve-condition xo parent)
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(encode (xoptional-type xo) val #:parent parent))
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(unless port-arg (get-output-bytes port))))
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(define (xoptional-size xo [val #f] #:parent [parent #f])
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(if (resolve-condition xo parent)
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(size (xoptional-type xo) val #:parent parent)
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0))
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(struct xoptional (type condition) #:transparent
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#:methods gen:xenomorphic
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[(define decode xoptional-decode)
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(define encode xoptional-encode)
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(define size xoptional-size)])
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(define (+xoptional type [condition #t])
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(xoptional type condition))
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