I've added a "trivial" random port in my CHICKEN implementation of the
current draft: <https://codeberg.org/phm/srfi-271-egg>

The trivial random port cyclically repeats an input bytevector. It can
be used to deterministically seed other random ports, and a long-enough
bytevector sourced from /dev/random can be used as a seed in most cases.

Example:

     (import (scheme base)
             (prefix (srfi 271 determinized trivial) tr:)
             (prefix (srfi 271 determinized) det:))

     (define seed #u8(1 2 3 4))
     (define port (tr:make-random-port seed))

     (read-bytevector port 4) ⇒ #u8(1 2 3 4)
     (read-u8 port) ⇒ 1
     (read-bytevector port 10) ⇒ #u8(2 3 4 1 2 3 4 1 2 3)

     (define state (tr:random-port-state port))
     (define new-port (tr:make-random-port state))

     (read-bytevector new-port 5) ⇒ #u8(4 1 2 3 4)
     (read-bytevector port 5) ⇒ #u8(4 1 2 3 4)

     (define some-other-random-algorithm-port
       (det:make-random-port port))
     ;; Will work except in pathological cases.
     ;; A 128 byte seed from a very random source like /dev/random
     ;; will likely be sufficient for all practical cases.

-- Peter McGoron