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37 lines
1.1 KiB
Racket
37 lines
1.1 KiB
Racket
#lang restructure/racket
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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/Pointer.coffee
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|#
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(define-subclass RestructureBase (Pointer offsetType type [scope 'local])
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(and (symbol? scope) (caseq scope
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[(local parent) 'yay]
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[else (raise-argument-error 'Pointer "local or parent" scope)]))
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(define/augride (decode stream ctx)
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(define offset (send offsetType decode stream ctx))
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(define ptr (+ offset (caseq scope
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[(local) (· this parent starting-offset)]
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[(parent) (· this parent parent starting-offset)])))
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(cond
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[type (define orig-pos (send stream pos))
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(send stream pos ptr)
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(define val (send type decode stream ctx))
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(send stream pos orig-pos)
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val]
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[else ptr]))
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(define/override (encode stream val)
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(error 'Pointer-encode-not-done))
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(define/override (size [val #f] [ctx #f])
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(report* this offsetType type (send type size)))
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) |