Creating an auto-complete-enabled prompt with readline-lib

[vinipsmaker]

I'm failing to make readline/readline's set-completion-function! work on Rhombus. This is what I came up with:

#lang rhombus

import:
    lib("readline/readline.rkt") as readline

fun on_completion(partial_input):
    readline.#{set-completion-append-character!}("!"[0])
    ["Rudolf", "Hermie", "Bumble", "Yukon", "Clarise", "Santa"].filter(~keep: fun(e): e.starts_with(partial_input))

readline.#{set-completion-function!}(on_completion)
readline.readline("my-shell> ")

The Racket version does work, so I don't understand why the Rhombus version doesn't work:

#lang racket

(require readline/readline)

(define (on_completion partial_input)
  (set-completion-append-character! #\!)
  (filter (lambda (e) (string-prefix? e partial_input))
          '("Rudolf" "Hermie" "Bumble" "Yukon" "Clarise" "Santa")))

(set-completion-function! on_completion)
(readline "my-shell> ")

[mflatt]

The problem is that a Rhombus list is not a Racket list, and the completion function wrapper doesn't complain about a non-Racket-list result. I'm not sure why the wrapper doesn't complain, but maybe it's because the callback is in atomic mode, so exceptions are unsafe at that point.

Adding PairList before ["Rudolf", .... makes it work.