TXR Lisp, with infix via ifx macro:

  (ifx
    (let ((a 0) (b 1) (c 0))
      (tagbody
       fb-start
        (prinl a)
        (b += a)
        (a := b - a)
        (c += 1)
        (if (c < 100)
          (go fb-start)))))