src/HOL/Tools/Sledgehammer/sledgehammer_minimize_isar.ML

robustness in degenerate case + tuning

(*  Title:      HOL/Tools/Sledgehammer/sledgehammer_minimize_isar.ML
    Author:     Steffen Juilf Smolka, TU Muenchen
    Author:     Jasmin Blanchette, TU Muenchen

Minimize dependencies (used facts) of Isar proof steps.
*)

signature SLEDGEHAMMER_MINIMIZE_ISAR =
sig
  type preplay_interface = Sledgehammer_Preplay.preplay_interface
  type isar_step = Sledgehammer_Proof.isar_step
  type isar_proof = Sledgehammer_Proof.isar_proof

  val min_deps_of_step : preplay_interface -> isar_step -> isar_step
  val postprocess_remove_unreferenced_steps : (isar_step -> isar_step) -> isar_proof -> isar_proof
end;

structure Sledgehammer_Minimize_Isar : SLEDGEHAMMER_MINIMIZE_ISAR =
struct

open Sledgehammer_Util
open Sledgehammer_Proof
open Sledgehammer_Preplay

val slack = seconds 0.1

fun min_deps_of_step (_ : preplay_interface) (step as Let _) = step
  | min_deps_of_step {get_preplay_time, set_preplay_time, preplay_quietly, ...}
      (step as Prove (qs, xs, l, t, subproofs, ((lfs, gfs), meth))) =
    (case get_preplay_time l of
      (* don't touch steps that time out or fail; minimizing won't help (not true -- FIXME) *)
      (true, _) => step
    | (false, time) =>
      let
        fun mk_step_lfs_gfs lfs gfs = Prove (qs, xs, l, t, subproofs, ((lfs, gfs), meth))
        val mk_step_gfs_lfs = curry (swap #> uncurry mk_step_lfs_gfs)

        fun minimize_facts _ time min_facts [] = (time, min_facts)
          | minimize_facts mk_step time min_facts (f :: facts) =
            (case preplay_quietly (Time.+ (time, slack)) (mk_step (min_facts @ facts)) of
              (true, _) => minimize_facts mk_step time (f :: min_facts) facts
            | (false, time) => minimize_facts mk_step time min_facts facts)

        val (time, min_lfs) = minimize_facts (mk_step_gfs_lfs gfs) time [] lfs
        val (time, min_gfs) = minimize_facts (mk_step_lfs_gfs min_lfs) time [] gfs
      in
        set_preplay_time l (false, time); mk_step_lfs_gfs min_lfs min_gfs
      end)

fun postprocess_remove_unreferenced_steps postproc_step =
  let
    val add_lfs = fold (Ord_List.insert label_ord)

    fun do_proof (Proof (fix, assms, steps)) =
      let val (refed, steps) = do_steps steps in
        (refed, Proof (fix, assms, steps))
      end
    and do_steps [] = ([], [])
      | do_steps steps =
        let
          (* the last step is always implicitly referenced *)
          val (steps, (refed, concl)) =
            split_last steps
            ||> do_refed_step
        in
          fold_rev do_step steps (refed, [concl])
        end
    and do_step step (refed, accu) =
      (case label_of_step step of
        NONE => (refed, step :: accu)
      | SOME l =>
          if Ord_List.member label_ord refed l then
            do_refed_step step
            |>> Ord_List.union label_ord refed
            ||> (fn x => x :: accu)
          else
            (refed, accu))
    and do_refed_step step = step |> postproc_step |> do_refed_step'
    and do_refed_step' (Let _) = raise Fail "Sledgehammer_Minimize_Isar"
      | do_refed_step' (Prove (qs, xs, l, t, subproofs, ((lfs, gfs), m))) =
        let
          val (refed, subproofs) =
            map do_proof subproofs
            |> split_list
            |>> Ord_List.unions label_ord
            |>> add_lfs lfs
          val step = Prove (qs, xs, l, t, subproofs, ((lfs, gfs), m))
        in
          (refed, step)
        end
  in
    snd o do_proof
  end

end;