How do I make completion work?

[playXE]

Here is a gist with completion implemented properly I think: https://gist.github.com/playXE/7a02ccabf6665b95c382531c8555eae4

But when I press TAB nothing is completed or displayed in REPL although eprintln!() inside complete does display possible completions.

[playXE]

nvm, I've implemented it incorrectly