random.ml

type gen = | Init | Gen of bool | Running of bool * bool * gen

let flip () = true
let one_in_three() = true

let rec generate g = 
  match g with
  | Init -> generate (Running (true, true, Init))
  | Gen b -> 
      if one_in_three() then 
        generate (Running (true, true, Gen b))
      else if b then
        generate (Running (true, false, Init)) else
        generate (Running (false, true, Init))
  | Running (true, false, x) -> (false, Running(false, false, x))
  | Running (false, true, x) -> (true, Running(false, false, x))
  | Running (true, true, x) ->
      if flip() then (false, Running(false, true, x)) else (true, Running(true, false, x))
  | Running (false, false, x) -> let (ret, x_) = generate x in (ret, Running(true, true, x_))