[edw]

Well, TCO seems to work:

    (define (count x)
      (let loop ((x x) (sum 0))
        (if (zero ? x)
          sum
          (loop  (- x 1) (+ sum x)))))
    
    (count 100000) ; ==> 5000050000 (doesn't blow up)

I'm very tempted to help out however I can. I've been dreaming of using Scheme instead of JS in a Node.js setting.