[racket] Reversing strings (Jay's article)

Mostly a question to Jay McCarthy but I suppose could be interesting to others. Was going over his Reversing strings article. Somehow I get weird performance. Slowest solution turns out fastest, medium, fast and really fast are only marginally different.

Could anyone have a look https://github.com/vkz/warm-up
reverse-string.rkt has the solutions
test-reverse-string.rkt does the performance check
Testing it on 40'000 randomly generated strings 1000 chars each.

While we're at it, why do we garbage-collect thrice here?
let-values ([(as cpu real gc) (time-apply (λ () exp) empty)])
    (collect-garbage) (collect-garbage) (collect-garbage)

Thanks!
---
Vlad Kozin <vladilen.kozin at gmail.com>



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