https://twitter.com/fermatslibrary/status/924263998589145090

e.fs

open System
open System.Collections.Generic

let samples = 100000

let rand = Random()

let lenTo1 () =
  Seq.unfold (fun sum -> if sum > 1.0 then None else Some ((), sum + rand.NextDouble ())) 0.0
  |> Seq.length

Seq.initInfinite (fun _ -> lenTo1 ())
|> Seq.take samples
|> Seq.map float
|> Seq.average
|> printfn "%f"