path: root/proofs/refiner.ml

(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(* $Id: refiner.ml 8708 2006-04-14 08:13:02Z jforest $ *)

open Pp
open Util
open Term
open Termops
open Sign
open Evd
open Sign
open Environ
open Reductionops
open Type_errors
open Proof_trees
open Proof_type
open Logic

type transformation_tactic = proof_tree -> (goal list * validation)

let hypotheses gl = gl.evar_hyps
let conclusion gl = gl.evar_concl

let sig_it x = x.it
let project x = x.sigma

let pf_status pf = pf.open_subgoals

let is_complete pf = (0 = (pf_status pf))

let on_open_proofs f pf = if is_complete pf then pf else f pf

let and_status = List.fold_left (+) 0

(* Getting env *)

let pf_env gls = Global.env_of_context (sig_it gls).evar_hyps
let pf_hyps gls = named_context_of_val (sig_it gls).evar_hyps

(* Normalizing evars in a goal. Called by tactic Local_constraints
   (i.e. when the sigma of the proof tree changes). Detect if the
   goal is unchanged *)
let norm_goal sigma gl =
  let red_fun = Evarutil.nf_evar sigma in
  let ncl = red_fun gl.evar_concl in
  let ngl =
    { evar_concl = ncl;
      evar_hyps = map_named_val red_fun gl.evar_hyps; 
      evar_body = gl.evar_body} in
  if Evd.eq_evar_info ngl gl then None else Some ngl


(* [mapshape [ l1 ; ... ; lk ] [ v1 ; ... ; vk ] [ p_1 ; .... ; p_(l1+...+lk) ]]
   gives
   [ (v1 [p_1 ... p_l1]) ; (v2 [ p_(l1+1) ... p_(l1+l2) ]) ; ... ;
   (vk [ p_(l1+...+l(k-1)+1) ... p_(l1+...lk) ]) ]
 *)

let rec mapshape nl (fl : (proof_tree list -> proof_tree) list) 
                    (l : proof_tree list) =
  match nl with
    | [] -> []
    | h::t ->
	let m,l = list_chop h l in 
	(List.hd fl m) :: (mapshape t (List.tl fl) l)

(* [frontier : proof_tree -> goal list * validation]
   given a proof [p], [frontier p] gives [(l,v)] where [l] is the list of goals
   to be solved to complete the proof, and [v] is the corresponding 
   validation *)
   
let rec frontier p =
  match p.ref with
    | None -> 
	([p.goal],
	 (fun lp' -> 
	    let p' = List.hd lp' in
            if Evd.eq_evar_info p'.goal p.goal then 
	      p'
            else 
	      errorlabstrm "Refiner.frontier"
                (str"frontier was handed back a ill-formed proof.")))
    | Some(r,pfl) ->
    	let gll,vl = List.split(List.map frontier pfl) in
    	(List.flatten gll,
         (fun retpfl ->
            let pfl' = mapshape (List.map List.length gll) vl retpfl in
            { open_subgoals = and_status (List.map pf_status pfl');
              goal = p.goal;
              ref = Some(r,pfl')}))


let rec frontier_map_rec f n p =
  if n < 1 || n > p.open_subgoals then p else
  match p.ref with
    | None -> 
        let p' = f p in
        if Evd.eq_evar_info p'.goal p.goal then p'
        else 
	  errorlabstrm "Refiner.frontier_map"
            (str"frontier_map was handed back a ill-formed proof.")
    | Some(r,pfl) ->
        let (_,rpfl') =
          List.fold_left
            (fun (n,acc) p -> (n-p.open_subgoals,frontier_map_rec f n p::acc))
            (n,[]) pfl in
        let pfl' = List.rev rpfl' in
        { open_subgoals = and_status (List.map pf_status pfl');
          goal = p.goal;
          ref = Some(r,pfl')}

let frontier_map f n p =
  let nmax = p.open_subgoals in
  let n = if n < 0 then nmax + n + 1 else n in
  if n < 1 || n > nmax then
    errorlabstrm "Refiner.frontier_map" (str "No such subgoal"); 
  frontier_map_rec f n p

let rec frontier_mapi_rec f i p =
  if p.open_subgoals = 0 then p else
  match p.ref with
    | None -> 
        let p' = f i p in
        if Evd.eq_evar_info p'.goal p.goal then p'
        else 
	  errorlabstrm "Refiner.frontier_mapi"
            (str"frontier_mapi was handed back a ill-formed proof.")
    | Some(r,pfl) ->
        let (_,rpfl') =
          List.fold_left
            (fun (n,acc) p -> (n+p.open_subgoals,frontier_mapi_rec f n p::acc))
            (i,[]) pfl in
        let pfl' = List.rev rpfl' in
        { open_subgoals = and_status (List.map pf_status pfl');
          goal = p.goal;
          ref = Some(r,pfl')}

let frontier_mapi f p = frontier_mapi_rec f 1 p

(* [list_pf p] is the lists of goals to be solved in order to complete the
   proof [p] *)

let list_pf p = fst (frontier p)

let rec nb_unsolved_goals pf = pf.open_subgoals

(* leaf g is the canonical incomplete proof of a goal g *)

let leaf g = {
  open_subgoals = 1;
  goal = g;
  ref = None }

(* Tactics table. *)

let tac_tab = Hashtbl.create 17

let add_tactic s t =
  if Hashtbl.mem tac_tab s then
    errorlabstrm ("Refiner.add_tactic: ") 
      (str ("Cannot redeclare tactic "^s));
  Hashtbl.add tac_tab s t

let overwriting_add_tactic s t =
  if Hashtbl.mem tac_tab s then begin
    Hashtbl.remove tac_tab s;
    warning ("Overwriting definition of tactic "^s)
  end;
  Hashtbl.add tac_tab s t

let lookup_tactic s =
  try 
    Hashtbl.find tac_tab s
  with Not_found -> 
    errorlabstrm "Refiner.lookup_tactic"
      (str"The tactic " ++ str s ++ str" is not installed")


(* refiner r is a tactic applying the rule r *)

let check_subproof_connection gl spfl =
  list_for_all2eq (fun g pf -> Evd.eq_evar_info g pf.goal) gl spfl

let abstract_tactic_expr te tacfun gls =
  let (sgl_sigma,v) = tacfun gls in
  let hidden_proof = v (List.map leaf sgl_sigma.it) in
  (sgl_sigma,
   fun spfl ->
     assert (check_subproof_connection sgl_sigma.it spfl);
     { open_subgoals = and_status (List.map pf_status spfl);
       goal = gls.it;
       ref = Some(Tactic(te,hidden_proof),spfl) })

let refiner = function
  | Prim pr as r ->
      let prim_fun = prim_refiner pr in
      (fun goal_sigma ->
         let sgl = prim_fun goal_sigma.sigma goal_sigma.it in 
	 ({it=sgl; sigma = goal_sigma.sigma},
          (fun spfl ->
	     assert (check_subproof_connection sgl spfl);
             { open_subgoals = and_status (List.map pf_status spfl);
               goal = goal_sigma.it;
               ref = Some(r,spfl) })))

  | Tactic _ -> failwith "Refiner: should not occur"
      
   (* [Local_constraints lc] makes the local constraints be [lc] and
      normalizes evars *)

  | Change_evars as r ->
      (fun goal_sigma ->
         let gl = goal_sigma.it in
         (match norm_goal goal_sigma.sigma gl with
             Some ngl ->
	       ({it=[ngl];sigma=goal_sigma.sigma},
                (fun spfl -> 
	          assert (check_subproof_connection [ngl] spfl);
                  { open_subgoals = (List.hd spfl).open_subgoals;
                    goal = gl;
                    ref = Some(r,spfl) }))
           (* if the evar change does not affect the goal, leave the
              proof tree unchanged *)
           | None -> ({it=[gl];sigma=goal_sigma.sigma},
                      (fun spfl ->
                        assert (List.length spfl = 1);
                        List.hd spfl))))


let local_Constraints gl = refiner Change_evars gl

let norm_evar_tac = local_Constraints

(*
let vernac_tactic (s,args) =
  let tacfun = lookup_tactic s args in
  abstract_extra_tactic s args tacfun
*)
let abstract_tactic te = abstract_tactic_expr (Tacexpr.TacAtom (dummy_loc,te))

let abstract_extended_tactic s args = 
  abstract_tactic (Tacexpr.TacExtend (dummy_loc, s, args))

let vernac_tactic (s,args) =
  let tacfun = lookup_tactic s args in
  abstract_extended_tactic s args tacfun

(* [extract_open_proof : proof_tree -> constr * (int * constr) list]
  takes a (not necessarly complete) proof and gives a pair (pfterm,obl)
  where pfterm is the constr corresponding to the proof
  and [obl] is an [int*constr list] [ (m1,c1) ; ... ; (mn,cn)]
  where the mi are metavariables numbers, and ci are their types.
  Their proof should be completed in order to complete the initial proof *)

let extract_open_proof sigma pf =
  let next_meta = 
    let meta_cnt = ref 0 in
    let rec f () =
      incr meta_cnt; 
      if in_dom sigma (existential_of_int !meta_cnt) then f ()
      else !meta_cnt
    in f
  in
  let open_obligations = ref [] in
  let rec proof_extractor vl = function
    | {ref=Some(Prim _,_)} as pf -> prim_extractor proof_extractor vl pf
	  
    | {ref=Some(Tactic (_,hidden_proof),spfl)} ->
	let sgl,v = frontier hidden_proof in
	let flat_proof = v spfl in
	proof_extractor vl flat_proof
	  
    | {ref=Some(Change_evars,[pf])} -> (proof_extractor vl) pf
	  
    | {ref=None;goal=goal} ->
	let visible_rels =
          map_succeed
            (fun id ->
               try let n = proof_variable_index id vl in (n,id)
	       with Not_found -> failwith "caught")
            (ids_of_named_context (named_context_of_val goal.evar_hyps)) in
	let sorted_rels =
	  Sort.list (fun (n1,_) (n2,_) -> n1 > n2 ) visible_rels in
        let sorted_env =
          List.map (fun (n,id) -> (n,lookup_named_val id goal.evar_hyps))
            sorted_rels in
	let abs_concl =
          List.fold_right (fun (_,decl) c -> mkNamedProd_or_LetIn decl c)
            sorted_env goal.evar_concl	in
        let inst = List.filter (fun (_,(_,b,_)) -> b = None) sorted_env in
        let meta = next_meta () in
	open_obligations := (meta,abs_concl):: !open_obligations;
	applist (mkMeta meta, List.map (fun (n,_) -> mkRel n) inst) 
	  
    | _ -> anomaly "Bug: a case has been forgotten in proof_extractor"
  in
  let pfterm = proof_extractor [] pf in
  (pfterm, List.rev !open_obligations)
  
(*********************)
(*   Tacticals       *)
(*********************)

(* unTAC : tactic -> goal sigma -> proof sigma *)

let unTAC tac g =
  let (gl_sigma,v) = tac g in 
  { it = v (List.map leaf gl_sigma.it); sigma = gl_sigma.sigma }

let unpackage glsig = (ref (glsig.sigma)),glsig.it

let repackage r v = {it=v;sigma = !r}

let apply_sig_tac r tac g =
  check_for_interrupt (); (* Breakpoint *) 
  let glsigma,v = tac (repackage r g) in 
  r := glsigma.sigma;
  (glsigma.it,v)

let idtac_valid = function
    [pf] -> pf
  | _ -> anomaly "Refiner.idtac_valid"

(* [goal_goal_list : goal sigma -> goal list sigma] *)
let goal_goal_list gls = {it=[gls.it];sigma=gls.sigma}

(* identity tactic without any message *)
let tclIDTAC gls = (goal_goal_list gls, idtac_valid)

(* the message printing identity tactic *)
let tclIDTAC_MESSAGE s gls = 
  msg (hov 0 s); tclIDTAC gls

(* General failure tactic *)
let tclFAIL_s s gls = errorlabstrm "Refiner.tclFAIL_s" (str s)

(* A special exception for levels for the Fail tactic *)
exception FailError of int * std_ppcmds

(* The Fail tactic *)
let tclFAIL lvl s g = raise (FailError (lvl,s))

let start_tac gls =
  let (sigr,g) = unpackage gls in
  (sigr,[g],idtac_valid)

let finish_tac (sigr,gl,p) = (repackage sigr gl, p)

(* Apply [taci.(i)] on the first n-th subgoals and [tac] on the others *)
let thensf_tac taci tac (sigr,gs,p) =
  let n = Array.length taci in
  let nsg = List.length gs in
  if nsg<n then errorlabstrm "Refiner.thensn_tac" (str "Not enough subgoals.");
  let gll,pl =
    List.split
      (list_map_i (fun i -> apply_sig_tac sigr (if i<n then taci.(i) else tac))
	0 gs) in
  (sigr, List.flatten gll,
   compose p (mapshape (List.map List.length gll) pl))

(* Apply [taci.(i)] on the last n-th subgoals and [tac] on the others *)
let thensl_tac tac taci (sigr,gs,p) =
  let n = Array.length taci in
  let nsg = List.length gs in
  if nsg<n then errorlabstrm "Refiner.thensn_tac" (str "Not enough subgoals.");
  let gll,pl =
    List.split
      (list_map_i (fun i -> apply_sig_tac sigr (if i<0 then tac else taci.(i)))
	(n-nsg) gs) in
  (sigr, List.flatten gll,
   compose p (mapshape (List.map List.length gll) pl))

(* Apply [tac i] on the ith subgoal (no subgoals number check) *)
let thensi_tac tac (sigr,gs,p) =
  let gll,pl =
    List.split (list_map_i (fun i -> apply_sig_tac sigr (tac i)) 1 gs) in
  (sigr, List.flatten gll, compose p (mapshape (List.map List.length gll) pl))

let then_tac tac = thensf_tac [||] tac

let non_existent_goal n =
  errorlabstrm ("No such goal: "^(string_of_int n))
    (str"Trying to apply a tactic to a non existent goal")

(* Apply tac on the i-th goal (if i>0). If i<0, then start counting from
   the last goal (i=-1). *)
let theni_tac i tac ((_,gl,_) as subgoals) =
  let nsg = List.length gl in
  let k = if i < 0 then nsg + i + 1 else i in
  if nsg < 1 then errorlabstrm "theni_tac" (str"No more subgoals.")
  else if k >= 1 & k <= nsg then
    thensf_tac
      (Array.init k (fun i -> if i+1 = k then tac else tclIDTAC)) tclIDTAC
      subgoals
  else non_existent_goal k 

(* [tclTHENSFIRSTn tac1 [|t1 ; ... ; tn|] tac2 gls] applies the tactic [tac1]
   to [gls] and applies [t1], ..., [tn] to the [n] first resulting
   subgoals, and [tac2] to the others subgoals. Raises an error if
   the number of resulting subgoals is strictly less than [n] *)
let tclTHENSFIRSTn tac1 taci tac gls =
  finish_tac (thensf_tac taci tac (then_tac tac1 (start_tac gls)))

(* [tclTHENSLASTn tac1 tac2 [|t1 ;...; tn|] gls] applies the tactic [tac1]
   to [gls] and applies [t1], ..., [tn] to the [n] last resulting
   subgoals, and [tac2] to the other subgoals. Raises an error if the
   number of resulting subgoals is strictly less than [n] *)
let tclTHENSLASTn tac1 tac taci gls =
  finish_tac (thensl_tac tac taci (then_tac tac1 (start_tac gls)))

(* [tclTHEN_i tac taci gls] applies the tactic [tac] to [gls] and applies
   [(taci i)] to the i_th resulting subgoal (starting from 1), whatever the
   number of subgoals is *)
let tclTHEN_i tac taci gls =
  finish_tac (thensi_tac taci (then_tac tac (start_tac gls)))

let tclTHENLASTn tac1 taci = tclTHENSLASTn tac1 tclIDTAC taci
let tclTHENFIRSTn tac1 taci = tclTHENSFIRSTn tac1 taci tclIDTAC

(* [tclTHEN tac1 tac2 gls] applies the tactic [tac1] to [gls] and applies
   [tac2] to every resulting subgoals *)
let tclTHEN tac1 tac2 = tclTHENSFIRSTn tac1 [||] tac2

(* [tclTHENSV tac1 [t1 ; ... ; tn] gls] applies the tactic [tac1] to
   [gls] and applies [t1],..., [tn] to the [n] resulting subgoals. Raises
   an error if the number of resulting subgoals is not [n] *)
let tclTHENSV tac1 tac2v =
  tclTHENSFIRSTn tac1 tac2v (tclFAIL_s "Wrong number of tactics.")

let tclTHENS tac1 tac2l = tclTHENSV tac1 (Array.of_list tac2l)

(* [tclTHENLAST tac1 tac2 gls] applies the tactic [tac1] to [gls] and [tac2]
   to the last resulting subgoal *)
let tclTHENLAST tac1 tac2 = tclTHENSLASTn tac1 tclIDTAC [|tac2|]

(* [tclTHENFIRST tac1 tac2 gls] applies the tactic [tac1] to [gls] and [tac2]
   to the first resulting subgoal *)
let tclTHENFIRST tac1 tac2 = tclTHENSFIRSTn tac1 [|tac2|] tclIDTAC


(* [tclTHENLIST [t1;..;tn]] applies [t1] then [t2] ... then [tn]. More
   convenient than [tclTHEN] when [n] is large. *)
let rec tclTHENLIST = function
    [] -> tclIDTAC
  | t1::tacl -> tclTHEN t1 (tclTHENLIST tacl)




(* various progress criterions *)
let same_goal gl subgoal = 
  eq_named_context_val (hypotheses subgoal) (hypotheses gl) &&
  eq_constr (conclusion subgoal) (conclusion gl)


let weak_progress gls ptree =
  (List.length gls.it <> 1) or 
  (not (same_goal (List.hd gls.it) ptree.it))

(* Il y avait ici un ts_eq ........ *)
let progress gls ptree =
  (weak_progress gls ptree) or
  (not (ptree.sigma == gls.sigma))


(* PROGRESS tac ptree applies tac to the goal ptree and fails if tac leaves
the goal unchanged *)
let tclPROGRESS tac ptree =
  let rslt = tac ptree in
  if progress (fst rslt) ptree then rslt
  else errorlabstrm "Refiner.PROGRESS" (str"Failed to progress.")

(* weak_PROGRESS tac ptree applies tac to the goal ptree and fails 
   if tac leaves the goal unchanged, possibly modifying sigma *)
let tclWEAK_PROGRESS tac ptree =
  let rslt = tac ptree in
  if weak_progress (fst rslt) ptree then rslt
  else errorlabstrm "Refiner.tclWEAK_PROGRESS" (str"Failed to progress.")


(* Same as tclWEAK_PROGRESS but fails also if tactics generates several goals,
   one of them being identical to the original goal *)
let tclNOTSAMEGOAL (tac : tactic) goal =
  let rslt = tac goal in
  let gls = (fst rslt).it in
  if List.exists (same_goal goal.it) gls
  then errorlabstrm "Refiner.tclNOTSAMEGOAL" 
      (str"Tactic generated a subgoal identical to the original goal.")
  else rslt



(* ORELSE0 t1 t2 tries to apply t1 and if it fails, applies t2 *)
let tclORELSE0 t1 t2 g =
  try 
    t1 g
  with (* Breakpoint *)
  | e when catchable_exception e -> check_for_interrupt (); t2 g
  | FailError (0,_) | Stdpp.Exc_located(_, FailError (0,_)) ->
      check_for_interrupt (); t2 g
  | FailError (lvl,s) -> raise (FailError (lvl - 1, s))
  | Stdpp.Exc_located (s,FailError (lvl,s')) ->
      raise (Stdpp.Exc_located (s,FailError (lvl - 1, s')))

(* ORELSE t1 t2 tries to apply t1 and if it fails or does not progress, 
   then applies t2 *)
let tclORELSE t1 t2 = tclORELSE0 (tclPROGRESS t1) t2

(* TRY f tries to apply f, and if it fails, leave the goal unchanged *)
let tclTRY f = (tclORELSE0 f tclIDTAC)

let tclTHENTRY f g = (tclTHEN f (tclTRY g))

(* Try the first tactic that does not fail in a list of tactics *)

let rec tclFIRST = function
  | [] -> tclFAIL_s "No applicable tactic."
  |  t::rest -> tclORELSE0 t (tclFIRST rest)

let ite_gen tcal tac_if continue tac_else gl=
  let success=ref false in
  let tac_if0 gl=
    let result=tac_if gl in
      success:=true;result in
  let tac_else0 e gl=
    if !success then 
      raise e 
    else 
      tac_else gl in
    try 
      tcal tac_if0 continue gl
    with (* Breakpoint *)
      | e when catchable_exception e ->
	  check_for_interrupt (); tac_else0 e gl
      | (FailError (0,_) | Stdpp.Exc_located(_, FailError (0,_))) as e ->
	  check_for_interrupt (); tac_else0 e gl
      | FailError (lvl,s) -> raise (FailError (lvl - 1, s))
      | Stdpp.Exc_located (s,FailError (lvl,s')) ->
	  raise (Stdpp.Exc_located (s,FailError (lvl - 1, s')))
	
(* Try the first tactic and, if it succeeds, continue with 
   the second one, and if it fails, use the third one *)

let tclIFTHENELSE=ite_gen tclTHEN

(* Idem with tclTHENS and tclTHENSV *)

let tclIFTHENSELSE=ite_gen tclTHENS

let tclIFTHENSVELSE=ite_gen tclTHENSV


(* Fails if a tactic did not solve the goal *)
let tclCOMPLETE tac = tclTHEN tac (tclFAIL_s "Proof is not complete.")

(* Try the first thats solves the current goal *)
let tclSOLVE tacl = tclFIRST (List.map tclCOMPLETE tacl)

			   
(* Iteration tacticals *)

let tclDO n t = 
  let rec dorec k = 
    if k < 0 then errorlabstrm "Refiner.tclDO"
      (str"Wrong argument : Do needs a positive integer.");
    if k = 0 then tclIDTAC
    else if k = 1 then t else (tclTHEN t (dorec (k-1)))
  in 
  dorec n 

(* Beware: call by need of CAML, g is needed *)
let rec tclREPEAT t g =
  (tclORELSE (tclTHEN t (tclREPEAT t)) tclIDTAC) g

let tclAT_LEAST_ONCE t = (tclTHEN t (tclREPEAT t))

(* Repeat on the first subgoal (no failure if no more subgoal) *)
let rec tclREPEAT_MAIN t g =
  (tclORELSE (tclTHEN_i t (fun i -> if i = 1 then (tclREPEAT_MAIN t) else
    tclIDTAC)) tclIDTAC) g

(*s Tactics handling a list of goals. *)

type validation_list = proof_tree list -> proof_tree list

type tactic_list = (goal list sigma) -> (goal list sigma) * validation_list

(* Functions working on goal list for correct backtracking in Prolog *)

let tclFIRSTLIST = tclFIRST
let tclIDTAC_list gls = (gls, fun x -> x)

(* first_goal : goal list sigma -> goal sigma *)

let first_goal gls = 
  let gl = gls.it and sig_0 = gls.sigma in 
  if gl = [] then error "first_goal"; 
  { it = List.hd gl; sigma = sig_0 }

(* goal_goal_list : goal sigma -> goal list sigma *)

let goal_goal_list gls = 
  let gl = gls.it and sig_0 = gls.sigma in { it = [gl]; sigma = sig_0 }

(* tactic -> tactic_list : Apply a tactic to the first goal in the list *)

let apply_tac_list tac glls = 
  let (sigr,lg) = unpackage glls in
  match lg with
  | (g1::rest) ->
      let (gl,p) = apply_sig_tac sigr tac g1 in
      let n = List.length gl in 
      (repackage sigr (gl@rest), 
       fun pfl -> let (pfg,pfrest) = list_chop n pfl in (p pfg)::pfrest)
  | _ -> error "apply_tac_list"
	  
let then_tactic_list tacl1 tacl2 glls = 
  let (glls1,pl1) = tacl1 glls in
  let (glls2,pl2) = tacl2 glls1 in
  (glls2, compose pl1 pl2)

(* Transform a tactic_list into a tactic *)

let tactic_list_tactic tac gls = 
    let (glres,vl) = tac (goal_goal_list gls) in
    (glres, compose idtac_valid vl)




(* The type of proof-trees state and a few utilities 
   A proof-tree state is built from a proof-tree, a set of global
   constraints, and a stack which allows to navigate inside the
   proof-tree remembering how to rebuild the global proof-tree
   possibly after modification of one of the focused children proof-tree.
   The number in the stack corresponds to 
   either the selected subtree and the validation is a function from a
   proof-tree list consisting only of one proof-tree to the global
   proof-tree 
   or -1 when the move is done behind a registered tactic in which
   case the validation corresponds to a constant function giving back 
   the original proof-tree. *)

type pftreestate = {
  tpf      : proof_tree ;
  tpfsigma : evar_map;
  tstack   : (int * validation) list }

let proof_of_pftreestate pts = pts.tpf
let is_top_pftreestate pts = pts.tstack = [] 
let cursor_of_pftreestate pts = List.map fst pts.tstack
let evc_of_pftreestate pts = pts.tpfsigma

let top_goal_of_pftreestate pts = 
  { it = goal_of_proof pts.tpf; sigma = pts.tpfsigma }

let nth_goal_of_pftreestate n pts =
  let goals = fst (frontier pts.tpf) in
  try {it = List.nth goals (n-1); sigma = pts.tpfsigma }
  with Invalid_argument _ | Failure _ -> non_existent_goal n

let descend n p =
  match p.ref with
    | None        -> error "It is a leaf."
    | Some(r,pfl) ->
    	if List.length pfl >= n then
	  (match list_chop (n-1) pfl with 
	     | left,(wanted::right) ->
		 (wanted,
		  (fun pfl' ->
                     if (List.length pfl' = 1) 
		       & (List.hd pfl').goal = wanted.goal 
		     then
                       let pf'       = List.hd pfl' in
                       let spfl      = left@(pf'::right) in
                       let newstatus = and_status (List.map pf_status spfl) in
                       { open_subgoals = newstatus;
			 goal          = p.goal;
			 ref           = Some(r,spfl) }
                     else 
		       error "descend: validation"))
	     | _ -> assert false)
    	else 
	  error "Too few subproofs"

let traverse n pts = match n with 
  | 0 -> (* go to the parent *)
      (match  pts.tstack with
	 | [] -> error "traverse: no ancestors"
	 | (_,v)::tl ->
	     { tpf = v [pts.tpf];
	       tstack = tl;
	       tpfsigma = pts.tpfsigma })
  | -1 -> (* go to the hidden tactic-proof, if any, otherwise fail *)
      (match pts.tpf.ref with
	 | Some (Tactic (_,spf),_) ->
	     let v = (fun pfl -> pts.tpf) in 
	     { tpf = spf;
               tstack = (-1,v)::pts.tstack;
               tpfsigma = pts.tpfsigma }
	 | _ -> error "traverse: not a tactic-node")
  | n -> (* when n>0, go to the nth child *)
      let (npf,v) = descend n pts.tpf in 
      { tpf = npf;
        tpfsigma = pts.tpfsigma;
        tstack = (n,v):: pts.tstack }

let change_constraints_pftreestate newgc pts = { pts with tpfsigma = newgc }

let app_tac sigr tac p =
  let (gll,v) = tac {it=p.goal;sigma= !sigr} in
  sigr := gll.sigma;
  v (List.map leaf gll.it)

(* solve the nth subgoal with tactic tac *)
let solve_nth_pftreestate n tac pts =
  let sigr = ref pts.tpfsigma in
  let tpf' = frontier_map (app_tac sigr tac) n pts.tpf in
  let tpf'' =
    if !sigr == pts.tpfsigma then tpf'
    else frontier_mapi (fun _ g -> app_tac sigr norm_evar_tac g) tpf' in
  { tpf      = tpf'';
    tpfsigma = !sigr;
    tstack   = pts.tstack }

let solve_pftreestate = solve_nth_pftreestate 1

(* This function implements a poor man's undo at the current goal.
   This is a gross approximation as it does not attempt to clean correctly
   the global constraints given in tpfsigma. *)

let weak_undo_pftreestate pts =
  let pf = leaf pts.tpf.goal in
  { tpf = pf;
    tpfsigma = pts.tpfsigma;
    tstack = pts.tstack }

(* Gives a new proof (a leaf) of a goal gl *)
let mk_pftreestate g =
  { tpf      = leaf g;
    tstack   = [];
    tpfsigma = Evd.empty }

(* Extracts a constr from a proof-tree state ; raises an error if the
   proof is not complete or the state does not correspond to the head
   of the proof-tree *)

let extract_open_pftreestate pts =
  extract_open_proof pts.tpfsigma pts.tpf

let extract_pftreestate pts =
  if pts.tstack <> [] then
    errorlabstrm "extract_pftreestate"
      (str"Cannot extract from a proof-tree in which we have descended;" ++
         spc () ++ str"Please ascend to the root");
  let pfterm,subgoals = extract_open_pftreestate pts in
  let exl = Evarutil.non_instantiated pts.tpfsigma in
  if subgoals <> [] or exl <> [] then
    errorlabstrm "extract_proof"
      (if subgoals <> [] then
        str "Attempt to save an incomplete proof"
      else
        str "Attempt to save a proof with existential variables still non-instantiated");
  let env = Global.env_of_context pts.tpf.goal.evar_hyps in
  nf_betaiotaevar_preserving_vm_cast env pts.tpfsigma pfterm
  (* strong whd_betaiotaevar env pts.tpfsigma pfterm *)
  (***
  local_strong (Evarutil.whd_ise (ts_it pts.tpfsigma)) pfterm
  ***)
(* Focus on the first leaf proof in a proof-tree state *)

let rec first_unproven pts =
  let pf = (proof_of_pftreestate pts) in 
  if is_complete_proof pf then
    errorlabstrm "first_unproven" (str"No unproven subgoals");
  if is_leaf_proof pf then
    pts
  else
    let childnum =
      list_try_find_i 
	(fun n pf -> 
	   if not(is_complete_proof pf) then n else failwith "caught")
	1 (children_of_proof pf)
    in 
    first_unproven (traverse childnum pts)

(* Focus on the last leaf proof in a proof-tree state *)

let rec last_unproven pts =
  let pf = proof_of_pftreestate pts in 
  if is_complete_proof pf then
    errorlabstrm "last_unproven" (str"No unproven subgoals");
  if is_leaf_proof pf then
    pts
  else 
    let children = (children_of_proof pf) in
    let nchilds = List.length children in
    let childnum =
      list_try_find_i 
        (fun n pf ->
           if not(is_complete_proof pf) then n else failwith "caught")
        1 (List.rev children)
    in 
    last_unproven (traverse (nchilds-childnum+1) pts)
      
let rec nth_unproven n pts =
  let pf = proof_of_pftreestate pts in 
  if is_complete_proof pf then
    errorlabstrm "nth_unproven" (str"No unproven subgoals");
  if is_leaf_proof pf then
    if n = 1 then 
      pts 
    else
      errorlabstrm "nth_unproven" (str"Not enough unproven subgoals")
  else 
    let children = children_of_proof pf in
    let rec process i k = function
      | [] -> 
	  errorlabstrm "nth_unproven" (str"Not enough unproven subgoals")
      | pf1::rest -> 
	  let k1 = nb_unsolved_goals pf1 in 
	  if k1 < k then 
	    process (i+1) (k-k1) rest
	  else 
	    nth_unproven k (traverse i pts)
    in 
    process 1 n children

let rec node_prev_unproven loc pts =
  let pf = proof_of_pftreestate pts in 
  match cursor_of_pftreestate pts with
    | [] -> last_unproven pts
    | n::l ->
	if is_complete_proof pf or loc = 1 then
          node_prev_unproven n (traverse 0 pts)
	else 
	  let child = List.nth (children_of_proof pf) (loc - 2) in
	  if is_complete_proof child then
	    node_prev_unproven (loc - 1) pts
	  else 
	    first_unproven (traverse (loc - 1) pts)

let rec node_next_unproven loc pts =
  let pf = proof_of_pftreestate pts in 
  match cursor_of_pftreestate pts with
    | [] -> first_unproven pts
    | n::l ->
	if is_complete_proof pf ||
           loc = (List.length (children_of_proof pf)) then
             node_next_unproven n (traverse 0 pts)
	else if is_complete_proof (List.nth (children_of_proof pf) loc) then
	  node_next_unproven (loc + 1) pts
	else 
	  last_unproven(traverse (loc + 1) pts)

let next_unproven pts =
  let pf = proof_of_pftreestate pts in 
  if is_leaf_proof pf then
    match cursor_of_pftreestate pts with
      | [] -> error "next_unproven"
      | n::_ -> node_next_unproven n (traverse 0 pts)
  else 
    node_next_unproven (List.length (children_of_proof pf)) pts

let prev_unproven pts =
  let pf = proof_of_pftreestate pts in 
  if is_leaf_proof pf then
    match cursor_of_pftreestate pts with
      | [] -> error "prev_unproven"
      | n::_ -> node_prev_unproven n (traverse 0 pts)
  else 
    node_prev_unproven 1 pts

let rec top_of_tree pts = 
  if is_top_pftreestate pts then pts else top_of_tree(traverse 0 pts)


(* Change evars *)
let tclEVARS sigma gls = tclIDTAC {gls with sigma=sigma}

(* Pretty-printers. *)

let pp_info = ref (fun _ _ _ -> assert false)
let set_info_printer f = pp_info := f

let tclINFO (tac : tactic) gls = 
  let (sgl,v) as res = tac gls in 
  begin try 
    let pf = v (List.map leaf (sig_it sgl)) in
    let sign = named_context_of_val (sig_it gls).evar_hyps in
    msgnl (hov 0 (str" == " ++
                  !pp_info (project gls) sign pf))
  with e when catchable_exception e -> 
    msgnl (hov 0 (str "Info failed to apply validation"))
  end;
  res