src/HOL/Tools/function_package/termination.ML

transferred code generator preprocessor into separate module

(*  Title:       HOL/Tools/function_package/termination.ML
    Author:      Alexander Krauss, TU Muenchen

Context data for termination proofs
*)


signature TERMINATION =
sig

  type data
  datatype cell = Less of thm | LessEq of (thm * thm) | None of (thm * thm) | False of thm

  val mk_sumcases : data -> typ -> term list -> term

  val note_measure : int -> term -> data -> data
  val note_chain   : term -> term -> thm option -> data -> data
  val note_descent : term -> term -> term -> cell -> data -> data

  val get_num_points : data -> int
  val get_types      : data -> int -> typ
  val get_measures   : data -> int -> term list

  (* read from cache *)
  val get_chain      : data -> term -> term -> thm option option
  val get_descent    : data -> term -> term -> term -> cell option

  (* writes *)
  val derive_descent  : theory -> tactic -> term -> term -> term -> data -> data
  val derive_descents : theory -> tactic -> term -> data -> data

  val dest_call : data -> term -> ((string * typ) list * int * term * int * term * term)

  val CALLS : (term list * int -> tactic) -> int -> tactic

  (* Termination tactics. Sequential composition via continuations. (2nd argument is the error continuation) *)
  type ttac = (data -> int -> tactic) -> (data -> int -> tactic) -> data -> int -> tactic

  val TERMINATION : Proof.context -> (data -> int -> tactic) -> int -> tactic

  val REPEAT : ttac -> ttac

  val wf_union_tac : Proof.context -> tactic
end



structure Termination : TERMINATION =
struct

open FundefLib

val term2_ord = prod_ord TermOrd.fast_term_ord TermOrd.fast_term_ord
structure Term2tab = TableFun(type key = term * term val ord = term2_ord);
structure Term3tab = TableFun(type key = term * (term * term) val ord = prod_ord TermOrd.fast_term_ord term2_ord);

(** Analyzing binary trees **)

(* Skeleton of a tree structure *)

datatype skel =
  SLeaf of int (* index *)
| SBranch of (skel * skel)


(* abstract make and dest functions *)
fun mk_tree leaf branch =
  let fun mk (SLeaf i) = leaf i
        | mk (SBranch (s, t)) = branch (mk s, mk t)
  in mk end


fun dest_tree split =
  let fun dest (SLeaf i) x = [(i, x)]
        | dest (SBranch (s, t)) x =
          let val (l, r) = split x
          in dest s l @ dest t r end
  in dest end


(* concrete versions for sum types *)
fun is_inj (Const ("Sum_Type.Inl", _) $ _) = true
  | is_inj (Const ("Sum_Type.Inr", _) $ _) = true
  | is_inj _ = false

fun dest_inl (Const ("Sum_Type.Inl", _) $ t) = SOME t
  | dest_inl _ = NONE

fun dest_inr (Const ("Sum_Type.Inr", _) $ t) = SOME t
  | dest_inr _ = NONE


fun mk_skel ps =
  let
    fun skel i ps =
      if forall is_inj ps andalso not (null ps)
      then let
          val (j, s) = skel i (map_filter dest_inl ps)
          val (k, t) = skel j (map_filter dest_inr ps)
        in (k, SBranch (s, t)) end
      else (i + 1, SLeaf i)
  in
    snd (skel 0 ps)
  end

(* compute list of types for nodes *)
fun node_types sk T = dest_tree (fn Type ("+", [LT, RT]) => (LT, RT)) sk T |> map snd

(* find index and raw term *)
fun dest_inj (SLeaf i) trm = (i, trm)
  | dest_inj (SBranch (s, t)) trm =
    case dest_inl trm of
      SOME trm' => dest_inj s trm'
    | _ => dest_inj t (the (dest_inr trm))



(** Matrix cell datatype **)

datatype cell = Less of thm | LessEq of (thm * thm) | None of (thm * thm) | False of thm;


type data =
  skel                            (* structure of the sum type encoding "program points" *)
  * (int -> typ)                  (* types of program points *)
  * (term list Inttab.table)      (* measures for program points *)
  * (thm option Term2tab.table)   (* which calls form chains? *)
  * (cell Term3tab.table)         (* local descents *)


fun map_measures f (p, T, M, C, D) = (p, T, f M, C, D)
fun map_chains f   (p, T, M, C, D) = (p, T, M, f C, D)
fun map_descent f  (p, T, M, C, D) = (p, T, M, C, f D)

fun note_measure p m = map_measures (Inttab.insert_list (op aconv) (p, m))
fun note_chain c1 c2 res = map_chains (Term2tab.update ((c1, c2), res))
fun note_descent c m1 m2 res = map_descent (Term3tab.update ((c,(m1, m2)), res))

(* Build case expression *)
fun mk_sumcases (sk, _, _, _, _) T fs =
  mk_tree (fn i => (nth fs i, domain_type (fastype_of (nth fs i))))
          (fn ((f, fT), (g, gT)) => (SumTree.mk_sumcase fT gT T f g, SumTree.mk_sumT fT gT))
          sk
  |> fst

fun mk_sum_skel rel =
  let
    val cs = FundefLib.dest_binop_list @{const_name Un} rel
    fun collect_pats (Const ("Collect", _) $ Abs (_, _, c)) =
      let
        val (Const ("op &", _) $ (Const ("op =", _) $ _ $ (Const ("Pair", _) $ r $ l)) $ Gam)
          = Term.strip_qnt_body "Ex" c
      in cons r o cons l end
  in
    mk_skel (fold collect_pats cs [])
  end

fun create ctxt T rel =
  let
    val sk = mk_sum_skel rel
    val Ts = node_types sk T
    val M = Inttab.make (map_index (apsnd (MeasureFunctions.get_measure_functions ctxt)) Ts)
  in
    (sk, nth Ts, M, Term2tab.empty, Term3tab.empty)
  end

fun get_num_points (sk, _, _, _, _) =
  let
    fun num (SLeaf i) = i + 1
      | num (SBranch (s, t)) = num t
  in num sk end

fun get_types (_, T, _, _, _) = T
fun get_measures (_, _, M, _, _) = Inttab.lookup_list M

fun get_chain (_, _, _, C, _) c1 c2 =
  Term2tab.lookup C (c1, c2)

fun get_descent (_, _, _, _, D) c m1 m2 =
  Term3tab.lookup D (c, (m1, m2))

fun dest_call D (Const ("Collect", _) $ Abs (_, _, c)) =
  let
    val n = get_num_points D
    val (sk, _, _, _, _) = D
    val vs = Term.strip_qnt_vars "Ex" c

    (* FIXME: throw error "dest_call" for malformed terms *)
    val (Const ("op &", _) $ (Const ("op =", _) $ _ $ (Const ("Pair", _) $ r $ l)) $ Gam)
      = Term.strip_qnt_body "Ex" c
    val (p, l') = dest_inj sk l
    val (q, r') = dest_inj sk r
  in
    (vs, p, l', q, r', Gam)
  end
  | dest_call D t = error "dest_call"


fun derive_desc_aux thy tac c (vs, p, l', q, r', Gam) m1 m2 D =
  case get_descent D c m1 m2 of
    SOME _ => D
  | NONE => let
    fun cgoal rel =
      Term.list_all (vs,
        Logic.mk_implies (HOLogic.mk_Trueprop Gam,
          HOLogic.mk_Trueprop (Const (rel, @{typ "nat => nat => bool"})
            $ (m2 $ r') $ (m1 $ l'))))
      |> cterm_of thy
    in
      note_descent c m1 m2
        (case try_proof (cgoal @{const_name HOL.less}) tac of
           Solved thm => Less thm
         | Stuck thm =>
           (case try_proof (cgoal @{const_name HOL.less_eq}) tac of
              Solved thm2 => LessEq (thm2, thm)
            | Stuck thm2 =>
              if prems_of thm2 = [HOLogic.Trueprop $ HOLogic.false_const]
              then False thm2 else None (thm2, thm)
            | _ => raise Match) (* FIXME *)
         | _ => raise Match) D
      end

fun derive_descent thy tac c m1 m2 D =
  derive_desc_aux thy tac c (dest_call D c) m1 m2 D

(* all descents in one go *)
fun derive_descents thy tac c D =
  let val cdesc as (vs, p, l', q, r', Gam) = dest_call D c
  in fold_product (derive_desc_aux thy tac c cdesc)
       (get_measures D p) (get_measures D q) D
  end

fun CALLS tac i st =
  if Thm.no_prems st then all_tac st
  else case Thm.term_of (Thm.cprem_of st i) of
    (_ $ (_ $ rel)) => tac (FundefLib.dest_binop_list @{const_name Un} rel, i) st
  |_ => no_tac st

type ttac = (data -> int -> tactic) -> (data -> int -> tactic) -> data -> int -> tactic

fun TERMINATION ctxt tac =
  SUBGOAL (fn (_ $ (Const (@{const_name "wf"}, wfT) $ rel), i) =>
  let
    val (T, _) = HOLogic.dest_prodT (HOLogic.dest_setT (domain_type wfT))
  in
    tac (create ctxt T rel) i
  end)


(* A tactic to convert open to closed termination goals *)
local
fun dest_term (t : term) = (* FIXME, cf. Lexicographic order *)
    let
      val (vars, prop) = FundefLib.dest_all_all t
      val (prems, concl) = Logic.strip_horn prop
      val (lhs, rhs) = concl
                         |> HOLogic.dest_Trueprop
                         |> HOLogic.dest_mem |> fst
                         |> HOLogic.dest_prod
    in
      (vars, prems, lhs, rhs)
    end

fun mk_pair_compr (T, qs, l, r, conds) =
    let
      val pT = HOLogic.mk_prodT (T, T)
      val n = length qs
      val peq = HOLogic.eq_const pT $ Bound n $ (HOLogic.pair_const T T $ l $ r)
      val conds' = if null conds then [HOLogic.true_const] else conds
    in
      HOLogic.Collect_const pT $
      Abs ("uu_", pT,
           (foldr1 HOLogic.mk_conj (peq :: conds')
            |> fold_rev (fn v => fn t => HOLogic.exists_const (fastype_of v) $ lambda v t) qs))
    end

in

fun wf_union_tac ctxt st =
    let
      val thy = ProofContext.theory_of ctxt
      val cert = cterm_of (theory_of_thm st)
      val ((trueprop $ (wf $ rel)) :: ineqs) = prems_of st

      fun mk_compr ineq =
          let
            val (vars, prems, lhs, rhs) = dest_term ineq
          in
            mk_pair_compr (fastype_of lhs, vars, lhs, rhs, map (ObjectLogic.atomize_term thy) prems)
          end

      val relation =
          if null ineqs then
              Const (@{const_name Set.empty}, fastype_of rel)
          else
              foldr1 (HOLogic.mk_binop @{const_name Un}) (map mk_compr ineqs)

      fun solve_membership_tac i =
          (EVERY' (replicate (i - 2) (rtac @{thm UnI2}))  (* pick the right component of the union *)
          THEN' (fn j => TRY (rtac @{thm UnI1} j))
          THEN' (rtac @{thm CollectI})                    (* unfold comprehension *)
          THEN' (fn i => REPEAT (rtac @{thm exI} i))      (* Turn existentials into schematic Vars *)
          THEN' ((rtac @{thm refl})                       (* unification instantiates all Vars *)
                 ORELSE' ((rtac @{thm conjI})
                          THEN' (rtac @{thm refl})
                          THEN' (blast_tac (local_claset_of ctxt))))  (* Solve rest of context... not very elegant *)
          ) i
    in
      ((PRIMITIVE (Drule.cterm_instantiate [(cert rel, cert relation)])
      THEN ALLGOALS (fn i => if i = 1 then all_tac else solve_membership_tac i))) st
    end


end


(* continuation passing repeat combinator *)
fun REPEAT ttac cont err_cont =
    ttac (fn D => fn i => (REPEAT ttac cont cont D i)) err_cont




end