I have a struct
(struct client-sock-addr (host port))
I have a toText function
(define (toText.v1 addr)
(string->chunked-string (format "<client-sock-addr ~a ~a>" (client-sock-addr-host addr) (client-sock-addr-port addr))))
When this code is executed, I get a contract violation error:
client-sock-addr-host: contract violation
expected: client-sock-addr?
given: #<client-sock-addr>
context...:
client-sock-addr-host
I am relatively new to Racket, and I have been reading over the docs, and I can't for the life of me figure out what #<...> means. It looks like it's what the REPL spits out when you construct an instance of the type, but then why does the function fail saying it's not of type client-sock-addr??
Thank you.
Unless it's a prefab structure, two calls to struct will create two different incompatible structure types, even if they have the same name and fields and printed representation. You can't pass a value created by the first struct's constructor to an accessor function of the second struct, which appears to be what's happening here.
A demonstration:
#lang racket/base
(module a racket/base
(provide x y)
(struct foo (bar))
(struct prefab-foo (bar) #:prefab)
(define x (foo 1))
(define y (prefab-foo 1)))
(require 'a)
(struct foo (bar))
(struct prefab-foo (bar) #:prefab)
(foo? x) ; #f
(prefab-foo? y); # t
#<client-sock-addr> is an example of an unreadable value; the default printed representation of an opaque struct (one that's not transparent or prefab) that doesn't have a custom write method.
(In other words, it is how Racket displays an object it doesn’t know how to display to you.)