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#lang racket/base
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(require racket/class
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"helper.rkt" "util.rkt" "number.rkt" "array.rkt" racket/stream racket/dict sugar/unstable/dict)
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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/LazyArray.coffee
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|#
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#;(define (xlazy-array-decode xla [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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))
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#;(define (xlazy-array-encode xla val [port-arg (current-output-port)] #:parent [parent #f])
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)
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#;(define (xlazy-array-size xla [val #f] #:parent [parent #f]))
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;; xarray-base holds type and len fields
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#;(struct xlazy-array xarray-base () #:transparent
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#:methods gen:xenomorphic
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[(define decode xlazy-array-decode)
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(define xdecode xlazy-array-decode)
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(define encode xlazy-array-encode)
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(define size xlazy-array-size)])
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(define xlazy-array%
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(class xarray-base%
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(super-new)
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(init-field lazy-type values)
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(inherit-field len)
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(define/override (xxdecode port parent)
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(define starting-pos (pos port)) ; ! placement matters. `resolve-length` will change `pos`
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(define decoded-len (resolve-length len #:parent parent))
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(let ([parent (if (xint? len)
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(mhasheq 'parent parent
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'_startOffset starting-pos
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'_currentOffset 0
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'_length len)
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parent)])
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(define starting-pos (pos port))
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(define type type)
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(begin0
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(for/stream ([index (in-range decoded-len)])
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(define orig-pos (pos port))
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(pos port (+ starting-pos (* (send type xxsize #f parent) index)))
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;; use explicit `port` arg below because this evaluation is delayed
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(begin0
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(send this post-decode (send type xxdecode port parent))
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(pos port orig-pos)))
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(pos port (+ (pos port) (* decoded-len (send type xxsize #f parent)))))))
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(define/override (xxencode val port [parent #f])
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(super xxencode (if (stream? val) (stream->list val) val) port parent))
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(define/override (xxsize [val #f] [parent #f])
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(super xxsize (if (stream? val) (stream->list val) val) parent))))
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(define (+xlazy-array [type-arg #f] [len-arg #f]
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#:type [type-kwarg #f]
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#:length [len-kwarg #f]
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#:subclass [class xlazy-array%])
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(define type (or type-arg type-kwarg))
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(define len (or len-arg len-kwarg))
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(unless (xenomorphic-type? type)
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(raise-argument-error '+xarray "xenomorphic type" type))
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(unless (length-resolvable? len)
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(raise-argument-error '+xarray "length-resolvable?" len))
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(new class [type type] [len len]))
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(module+ test
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(require rackunit "number.rkt" "generic.rkt")
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(define bstr #"ABCD1234")
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(define ds (open-input-bytes bstr))
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(define la (+xlazy-array uint8 4))
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(define ila (decode la ds))
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(check-equal? (pos ds) 4)
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(check-equal? (stream-ref ila 1) 66)
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(check-equal? (stream-ref ila 3) 68)
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(check-equal? (pos ds) 4)
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(check-equal? (stream->list ila) '(65 66 67 68))
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(define la2 (+xlazy-array int16be (λ (t) 4)))
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(check-equal? (encode la2 '(1 2 3 4) #f) #"\0\1\0\2\0\3\0\4")
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(check-equal? (stream->list (decode la2 (open-input-bytes #"\0\1\0\2\0\3\0\4"))) '(1 2 3 4))) |