open System
 
type SeqDesc<'a> = SeqDesc of 'a * (unit -> SeqDesc<'a>) //' a self referring tuple type
 
let primesMPWSE () =   // original code by GordonBGood,  http://stackoverflow.com/a/17401770/849891 
  let wh = [| 2;4;2;4;6;2;6;4;2;4;6;6;2;6;4;2;6;4;6;8;4;2;4;2;
                4;8;6;4;6;2;4;6;2;6;6;4;2;4;6;2;6;4;2;4;2;10;2;10 |]   
  let inline adv i = if i < 47 then i + 1 else 0
  let reinsert c m (p,pi) =
      let c2 = c + wh.[pi] * p
      match Map.tryFind c2 m with
        | None        -> m |> Map.add c2 [(p,adv pi)]
        | Some(facts) -> m |> Map.add c2 ((p,adv pi)::facts)
  let rec mkprimes (n,i) m (SeqDesc((p,pi),f) as psd) q =   
    let n2,i2 = n + wh.[i],adv i
 
    match Map.tryFind n m with
      | None -> if n < q then SeqDesc((n,i),fun() -> mkprimes (n2,i2) m psd q)
                else let (SeqDesc((p2,_),_) as nsd),c2 = f(),n + wh.[pi] * p
                     mkprimes (n2,i2) (Map.add c2 [(p,adv pi)] m) nsd (p2 * p2)
      | Some(skips) -> let m2 = skips |> List.fold (reinsert n) (m |> Map.remove n)
                       mkprimes (n2,i2) m2 psd q
  let rec prs = SeqDesc((11,0),fun() -> mkprimes (13,1) Map.empty prs 121 )
  let genseq sd = Seq.unfold (fun (SeqDesc((p,_), g)) -> Some(p, g())) sd
  seq { yield 2; yield 3; yield 5; yield 7; yield! mkprimes (11,0) Map.empty prs 121 |> genseq }
 
primesMPWSE() |> Seq.nth 100000 |> printfn "%A"

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

-- with wh etc internal to mkprimes:     -- external to mkprimes:        --  ()
100k: 1299721: 1.26s 12.7MB                    1.06s                    1.06s    12.6MB
200k: 2750161: 2.53s 12.9MB    n^1.01          2.33s                    2.21s    12.6MB
400k: 5800139: 5.61s 12.7MB    n^1.15
800k: 12195263 12.3s 12.9MB    n^1.13         11.11s   n^1.13          10.84s    12.6MB (11.06-12.8)??
1mln:         -15.7s-                         14.33s   n^1.13          14.15s    12.9MB (limit exceeded)??