fixed-point (pseudo) evaluation

eval_stable.ml

  let eval_stable n one_step x : lambda * int =
    let ctr = new Gen.counter 0 in
    let tick () = ctr # inc in
    let step = one_step tick in
    let rec aux x prev =
      let curr = ctr # get in
      if prev = curr  then
        x
      else if ctr#get > n then (
        print_endline ("exceeded "^(string_of_int n)^" reductions");
        x
      )
      else
        (* if we encounter a let, fudge curr to allow one more run of step *)
        let curr =
          if match x with |Let _ -> true | _ -> false
          then curr-1
          else curr in
        aux (step x) curr in
    (* start with -1 so we run step at least once *)
    let r=aux x (ctr#get - 1) in
      (r,ctr#get);;