1.fs

let cell (x: 'a) : Job<Cell<'a>> = job {
  let c = {reqCh = Ch (); replyCh = Ch ()}
  let rec server x = job {
        let! req = Ch.take c.reqCh
        match req with
         | Get ->
           do! Ch.give c.replyCh x
           return! server x
         | Put x ->
           return! server x
      }
  do! Job.start (server x)
  return c
}

2.fs

let create (x: 'a) : Job<Cell<'a>> = Job.delay <| fun () ->
  let c = {reqCh = Ch (); replyCh = Ch ()}
  let rec server x =
    Ch.take c.reqCh >>= function
     | Get ->
       Ch.give c.replyCh x >>=. server x
     | Put x -> server x       
  Job.start (server x) >>-. c

3.fs

let create x = Job.delay <| fun () ->
  let c = {reqCh = Ch (); replyCh = Ch ()}
  Job.iterateServer x <| fun x ->
        c.reqCh >>= function
          | Get -> c.replyCh *<- x >>-. x
          | Put x -> Job.result x
  >>-. c