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56 lines
1.8 KiB
Racket
56 lines
1.8 KiB
Racket
#lang racket/base
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(require racket/class
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racket/contract
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"base.rkt"
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"util.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/Reserved.coffee
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|#
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(define x:reserved%
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(class x:base%
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(super-new)
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(init-field [(@type type)] [(@count count)])
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(unless (xenomorphic? @type)
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(raise-argument-error 'x:reserved "xenomorphic type" @type))
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(define/augment (x:decode port parent)
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(pos port (+ (pos port) (x:size #f parent)))
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(void))
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(define/augment (x:encode val port [parent #f])
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(make-bytes (x:size val parent) 0))
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(define/augment (x:size [val #f] [parent #f])
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(* (send @type x:size) (resolve-length @count #f parent)))))
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(define (x:reserved? x) (is-a? x x:reserved%))
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(define/contract (x:reserved [type-arg #f]
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[count-arg #f]
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#:type [type-kwarg #f]
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#:count [count-kwarg 1]
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#:pre-encode [pre-proc #f]
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#:post-decode [post-proc #f]
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#:base-class [base-class x:reserved%])
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(()
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((or/c xenomorphic? #false)
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(or/c exact-positive-integer? #false)
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#:type (or/c xenomorphic? #false)
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#:count exact-positive-integer?
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#:pre-encode (or/c (any/c . -> . any/c) #false)
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#:post-decode (or/c (any/c . -> . any/c) #false)
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#:base-class (λ (c) (subclass? c x:reserved%)))
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. ->* .
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x:reserved?)
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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 'x:reserved "xenomorphic type" type))
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(define count (or count-arg count-kwarg))
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(new (generate-subclass base-class pre-proc post-proc)
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[type type]
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[count count])) |