If I have a struct that wraps an input-port, and I want the struct to be
usable as an event that returns the struct as the sync result... is
there an better way than the code below?
In the code below, I am using "letrec" to get around the fact that
AFAIK, I need my "wrap-evt" proc arg to reference the struct itself, I
don't have a reference to the struct while the struct is being
contructed, and "prop:evt" won't let me reference a mutable field.
#lang racket/base
(struct my-struct
(my-wrapped-evt
my-wrapping-evt)
#:property prop:evt (struct-field-index my-wrapping-evt))
(define (my-struct* my-wrapped-evt)
(letrec ((my-wrapping-evt (wrap-evt my-wrapped-evt
(lambda (ignored-wrapped-evt)
s)))
(s (my-struct my-wrapped-evt
my-wrapping-evt)))
s))
(define (my-struct-read s)
(read-byte (my-struct-my-wrapped-evt s)))
;; Test:
(define s (my-struct* (current-input-port)))
(printf "s = ~S\n" s)
(let loop ()
(write-string "Syncing...\n")
(let ((my-evt-result (sync s)))
(printf "Reading from ~S...\n" my-evt-result)
(let ((v (my-struct-read s)))
(printf "Read ~S\n" v)
(loop))))
(The reason I am wrapping an input port this way is because the struct
ADT in my real program does bigger stuff whenever at least 1 byte is
available on the port, not just return the single byte.)
Neil V.
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