Generate prime numbers using an online Sieve of Eratosthenes

Primes.tq

let primes =
  let a = {2} in
  let grow() =
    let p0 = Array.get a (Array.length a - 1) + 1 in
    let b = Array.init p0 [_ → True] in
    let () =
      Array.fold [(), di →
        let rec loop i =
          if i >= Array.length b then () else
            let () = Array.Unsafe.set b i False in
            loop(i+di) in
        let i0 = floor(p0 / di) * di in
        loop(if i0<p0 then i0+di-p0 else i0-p0) ] () a in
    let f ((a, i), b) =
      (if b then Array.Unsafe.append a (p0+i) else a), i+1 in
    let _ = Array.fold f (a, 0) b in
    () in
  let rec loop n =
    if n < Array.length a then Array.get a n else
      let () = grow() in
      loop n in
  loop