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#lang debug 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/post-decode (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/pre-encode (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/finalize-size (xoptional-size xo [val #f] #:parent [parent #f])
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(when (resolve-condition xo parent)
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(size (xoptional-type xo) val #:parent parent)))
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(struct xoptional xbase (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-arg #f] [cond-arg #f]
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#:type [type-kwarg #f]
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#:condition [cond-kwarg #f])
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(define type (or type-arg type-kwarg))
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(unless (xenomorphic? type)
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(raise-argument-error '+xoptional"xenomorphic type" type))
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(define condition (or cond-arg cond-kwarg))
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(xoptional type condition))
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(define no-val (gensym))
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(define (+xoptional [type-arg #f] [cond-arg no-val]
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#:type [type-kwarg #f]
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#:condition [cond-kwarg no-val])
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(define type (or type-arg type-kwarg))
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(unless (xenomorphic? type)
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(raise-argument-error '+xoptional"xenomorphic type" type))
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(define condition (cond
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[(and (eq? cond-arg no-val) (eq? cond-kwarg no-val)) #true]
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[(not (eq? cond-arg no-val)) cond-arg]
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[(not (eq? cond-kwarg no-val)) cond-kwarg]))
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(xoptional type condition))
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