(loop for i fixnum from 1 to 100000000 sum (/ 1.0d0 i) double-float)

#lang typed/racket

(define: (test) : Float
         (for/fold: : Float
                    ([s : Float 0.0])
                    ([i : Fixnum (in-range 1 100000001)])
                    (+ s (/ 1.0 i))))

(time (test))

#lang typed/racket

(require syntax/parse/define)

(define-simple-macro (for/flsum x ... (c ...) b ... e)
  (for/fold : Float x ... ([s 0.0]) (c ...) b ... (+ s e)))

(time (for/flsum ([i : Positive-Fixnum (in-range 1 100000001)]) (/ 1.0 i)))