(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2011     *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(*i $Id: mlutil.ml 14786 2011-12-10 12:55:19Z letouzey $ i*)

(*i*)

open Coq
open OcamlExtractionTable
open Miniml
(*i*)

(*s Exceptions. *)

exception Found
exception Impossible

(*S Names operations. *)

let anonymous_name = "x"
let dummy_name = "_"

let anonymous = Id anonymous_name

let id_of_name = function
  | "_" -> anonymous_name
  | id -> id

let id_of_mlid = function
  | Dummy -> dummy_name
  | Id id -> id
  | Tmp id -> id

let tmp_id = function
  | Id id -> Tmp id
  | a -> a

let is_tmp = function Tmp _ -> true | _ -> false

(*S Operations upon ML types (with meta). *)

let meta_count = ref 0

let reset_meta_count () = meta_count := 0

let new_meta _ =
  incr meta_count;
  Tmeta {id = !meta_count; contents = None}

(*s Sustitution of [Tvar i] by [t] in a ML type. *)

let type_subst i t0 t =
  let rec subst t = match t with
    | Tvar j when i = j -> t0
    | Tmeta {contents=None} -> t
    | Tmeta {contents=Some u} -> subst u
    | Tarr (a,b) -> Tarr (subst a, subst b)
    | Tglob (r, l) -> Tglob (r, List.map subst l)
    | a -> a
  in subst t

(* Simultaneous substitution of [[Tvar 1; ... ; Tvar n]] by [l] in a ML type. *)

let type_subst_list l t =
  let rec subst t = match t with
    | Tvar j -> List.nth l (j-1)
    | Tmeta {contents=None} -> t
    | Tmeta {contents=Some u} -> subst u
    | Tarr (a,b) -> Tarr (subst a, subst b)
    | Tglob (r, l) -> Tglob (r, List.map subst l)
    | a -> a
  in subst t

(* Simultaneous substitution of [[|Tvar 1; ... ; Tvar n|]] by [v] in a ML type. *)

let type_subst_vect v t =
  let rec subst t = match t with
    | Tvar j -> v.(j-1)
    | Tmeta {contents=None} -> t
    | Tmeta {contents=Some u} -> subst u
    | Tarr (a,b) -> Tarr (subst a, subst b)
    | Tglob (r, l) -> Tglob (r, List.map subst l)
    | a -> a
  in subst t

(*s From a type schema to a type. All [Tvar] become fresh [Tmeta]. *)

let instantiation (nb,t) = type_subst_vect (Array.init nb new_meta) t

(*s Occur-check of a free meta in a type *)

let rec type_occurs alpha t =
  match t with
  | Tmeta {id=beta; contents=None} -> alpha = beta
  | Tmeta {contents=Some u} -> type_occurs alpha u
  | Tarr (t1, t2) -> type_occurs alpha t1 || type_occurs alpha t2
  | Tglob (_r,l) -> List.exists (type_occurs alpha) l
  | _ -> false

(*s Most General Unificator *)

let rec mgu = function
  | Tmeta m, Tmeta m' when m.id = m'.id -> ()
  | Tmeta m, t | t, Tmeta m ->
    (match m.contents with
      | Some u -> mgu (u, t)
      | None when type_occurs m.id t -> raise Impossible
      | None -> m.contents <- Some t)
  | Tarr(a, b), Tarr(a', b') ->
      mgu (a, a'); mgu (b, b')
  | Tglob (r,l), Tglob (r',l') when r = r' ->
       List.iter mgu (List.combine l l')
  | Tdummy _, Tdummy _ -> ()
  | t, u when t = u -> () (* for Tvar, Tvar', Tunknown, Taxiom *)
  | _ -> raise Impossible

let needs_magic p = try mgu p; false with Impossible -> true

let put_magic_if b a = if b then MLmagic a else a

let put_magic p a = if needs_magic p then MLmagic a else a

let generalizable a =
    match a with
      | MLapp _ -> false
      | _ -> true (* TODO, this is just an approximation for the moment *)

(*S ML type env. *)

module Mlenv = struct

  let meta_cmp m m' = compare m.id m'.id
  module Metaset = Set.Make(struct type t = ml_meta let compare = meta_cmp end)

  (* Main MLenv type. [env] is the real environment, whereas [free]
     (tries to) record the free meta variables occurring in [env]. *)

  type t = { env : ml_schema list; mutable free : Metaset.t}

  (* Empty environment. *)

  let empty = { env = []; free = Metaset.empty }

  (* [get] returns a instantiated copy of the n-th most recently added
     type in the environment. *)

  let get mle n =
    assert (List.length mle.env >= n);
    instantiation (List.nth mle.env (n-1))

  (* [find_free] finds the free meta in a type. *)

  let rec find_free set = function
    | Tmeta m when m.contents = None -> Metaset.add m set
    | Tmeta {contents = Some t} -> find_free set t
    | Tarr (a,b) -> find_free (find_free set a) b
    | Tglob (_,l) -> List.fold_left find_free set l
    | _ -> set

  (* The [free] set of an environment can be outdate after
     some unifications. [clean_free] takes care of that. *)

  let clean_free mle =
    let rem = ref Metaset.empty
    and add = ref Metaset.empty in
    let clean m = match m.Miniml.contents with
      | None -> ()
      | Some u -> rem := Metaset.add m !rem; add := find_free !add u
    in
    Metaset.iter clean mle.free;
    mle.free <- Metaset.union (Metaset.diff mle.free !rem) !add

  (* From a type to a type schema. If a [Tmeta] is still uninstantiated
     and does appears in the [mle], then it becomes a [Tvar]. *)

  let generalization mle t =
    let c = ref 0 in
    let map = ref (Intmap.empty : int Intmap.t) in
    let add_new i = incr c; map := Intmap.add i !c !map; !c in
    let rec meta2var t = match t with
      | Tmeta {contents=Some u} -> meta2var u
      | Tmeta ({id=i} as m) ->
	  (try Tvar (Intmap.find i !map)
	   with Not_found ->
	     if Metaset.mem m mle.free then t
	     else Tvar (add_new i))
      | Tarr (t1,t2) -> Tarr (meta2var t1, meta2var t2)
      | Tglob (r,l) -> Tglob (r, List.map meta2var l)
      | t -> t
    in !c, meta2var t

  (* Adding a type in an environment, after generalizing. *)

  let push_gen mle t =
    clean_free mle;
    { env = generalization mle t :: mle.env; free = mle.free }

  (* Adding a type with no [Tvar], hence no generalization needed. *)

  let push_type {env=e;free=f} t =
    { env = (0,t) :: e; free = find_free f t}

  (* Adding a type with no [Tvar] nor [Tmeta]. *)

  let push_std_type {env=e;free=f} t =
    { env = (0,t) :: e; free = f}

end

(*S Operations upon ML types (without meta). *)

(*s Does a section path occur in a ML type ? *)

let rec type_mem_kn uri = 
 function
  | Tmeta {contents = Some t} -> type_mem_kn uri t
  | Tglob (r,l) ->
     let NReference.Ref (uri',_) = r in
      NUri.eq uri uri' || List.exists (type_mem_kn uri) l
  | Tarr (a,b) -> (type_mem_kn uri a) || (type_mem_kn uri b)
  | _ -> false

(*s Greatest variable occurring in [t]. *)

let type_maxvar t =
  let rec parse n = function
    | Tmeta {contents = Some t} -> parse n t
    | Tvar i -> max i n
    | Tarr (a,b) -> parse (parse n a) b
    | Tglob (_,l) -> List.fold_left parse n l
    | _ -> n
  in parse 0 t

(*s What are the type variables occurring in [t]. *)

(*let intset_union_map_list f l =
  List.fold_left (fun s t -> Intset.union s (f t)) Intset.empty l*)

(*let intset_union_map_array f a =
  Array.fold_left (fun s t -> Intset.union s (f t)) Intset.empty a*)

(*let rec type_listvar = function
  | Tmeta {contents = Some t} -> type_listvar t
  | Tvar i | Tvar' i -> Intset.singleton i
  | Tarr (a,b) -> Intset.union (type_listvar a) (type_listvar b)
  | Tglob (_,l) -> intset_union_map_list type_listvar l
  | _ -> Intset.empty*)

(*s From [a -> b -> c] to [[a;b],c]. *)

let rec type_decomp = function
  | Tmeta {contents = Some t} -> type_decomp t
  | Tarr (a,b) -> let l,h = type_decomp b in a::l, h
  | a -> [],a

(*s The converse: From [[a;b],c] to [a -> b -> c]. *)

let rec type_recomp (l,t) = match l with
  | [] -> t
  | a::l -> Tarr (a, type_recomp (l,t))

(*s Translating [Tvar] to [Tvar'] to avoid clash. *)

let rec var2var' = function
  | Tmeta {contents = Some t} -> var2var' t
  | Tvar i -> Tvar' i
  | Tarr (a,b) -> Tarr (var2var' a, var2var' b)
  | Tglob (r,l) -> Tglob (r, List.map var2var' l)
  | a -> a

type 'status abbrev_map =
 'status -> NReference.reference -> ('status * ml_type) option

(*s Delta-reduction of type constants everywhere in a ML type [t].
   [env] is a function of type [ml_type_env]. *)

let type_expand status env t =
  let rec expand status = function
    | Tmeta {contents = Some t} -> expand status t
    | Tglob (r,l) ->
	(match env status r with
	   | Some (status,mlt) -> expand status (type_subst_list l mlt)
	   | None ->
              let status,l =
               List.fold_right
                (fun t (status,res) ->
                  let status,res' = expand status t in
                   status,res'::res)
                l (status,[])
              in
               status,Tglob (r, l))
    | Tarr (a,b) ->
       let status,a = expand status a in
       let status,b = expand status b in
        status,Tarr (a,b)
    | a -> status,a in
  if OcamlExtractionTable.type_expand () then
   expand status t
  else
   status,t

let type_simpl status = type_expand status (fun _ _ -> None)

(*s Generating a signature from a ML type. *)

let type_to_sign status env t =
 let status,res = type_expand status env t in
  status,
   match res with
    | Tdummy d -> Kill d
    | _ -> Keep

let type_to_signature status env t =
  let rec f = function
    | Tmeta {contents = Some t} -> f t
    | Tarr (Tdummy d, b) -> Kill d :: f b
    | Tarr (_, b) -> Keep :: f b
    | _ -> []
  in
   let status,res = type_expand status env t in
    status,f res

let isKill = function Kill _ -> true | _ -> false

let isDummy = function Tdummy _ -> true | _ -> false

let sign_of_id = function
  | Dummy -> Kill Kother
  | _ -> Keep

(* Classification of signatures *)

type sign_kind =
  | EmptySig
  | NonLogicalSig (* at least a [Keep] *)
  | UnsafeLogicalSig (* No [Keep], at least a [Kill Kother] *)
  | SafeLogicalSig (* only [Kill Ktype] *)

let rec sign_kind = function
  | [] -> EmptySig
  | Keep :: _ -> NonLogicalSig
  | Kill k :: s ->
      match sign_kind s with
	| NonLogicalSig -> NonLogicalSig
	| UnsafeLogicalSig -> UnsafeLogicalSig
	| SafeLogicalSig | EmptySig ->
	    if k = Kother then UnsafeLogicalSig else SafeLogicalSig

(* Removing the final [Keep] in a signature *)

let rec sign_no_final_keeps = function
  | [] -> []
  | k :: s ->
      let s' = k :: sign_no_final_keeps s in
      if s' = [Keep] then [] else s'

(*s Removing [Tdummy] from the top level of a ML type. *)

let type_expunge_from_sign status env s t =
  let rec expunge status s t =
    if s = [] then status,t else match t with
      | Tmeta {contents = Some t} -> expunge status s t
      | Tarr (a,b) ->
	  let status,t = expunge status (List.tl s) b in
	  status, if List.hd s = Keep then Tarr (a, t) else t
      | Tglob (r,l) ->
	  (match env status r with
	     | Some (status,mlt) -> expunge status s (type_subst_list l mlt)
	     | None -> assert false)
      | _ -> assert false
  in
  let status,t = expunge status (sign_no_final_keeps s) t in
  status,
   if sign_kind s = UnsafeLogicalSig then
     Tarr (Tdummy Kother, t)
   else t

let type_expunge status env t =
 let status,res = type_to_signature status env t in
  type_expunge_from_sign status env res t

(*S Generic functions over ML ast terms. *)

let mlapp f a = if a = [] then f else MLapp (f,a)

(*s [ast_iter_rel f t] applies [f] on every [MLrel] in t. It takes care
   of the number of bingings crossed before reaching the [MLrel]. *)

let ast_iter_rel f =
  let rec iter n = function
    | MLrel i -> f (i-n)
    | MLlam (_,a) -> iter (n+1) a
    | MLletin (_,a,b) -> iter n a; iter (n+1) b
    | MLcase (_,a,v) ->
	iter n a; Array.iter (fun (_,l,t) -> iter (n + (List.length l)) t) v
    | MLfix (_,ids,v) -> let k = Array.length ids in Array.iter (iter (n+k)) v
    | MLapp (a,l) -> iter n a; List.iter (iter n) l
    | MLcons (_,_,l) ->  List.iter (iter n) l
    | MLmagic a -> iter n a
    | MLglob _ | MLexn _ | MLdummy | MLaxiom -> ()
  in iter 0

(*s Map over asts. *)

let ast_map_case f (c,ids,a) = (c,ids,f a)

let ast_map f = function
  | MLlam (i,a) -> MLlam (i, f a)
  | MLletin (i,a,b) -> MLletin (i, f a, f b)
  | MLcase (i,a,v) -> MLcase (i,f a, Array.map (ast_map_case f) v)
  | MLfix (i,ids,v) -> MLfix (i, ids, Array.map f v)
  | MLapp (a,l) -> MLapp (f a, List.map f l)
  | MLcons (i,c,l) -> MLcons (i,c, List.map f l)
  | MLmagic a -> MLmagic (f a)
  | MLrel _ | MLglob _ | MLexn _ | MLdummy | MLaxiom as a -> a

(*s Map over asts, with binding depth as parameter. *)

let ast_map_lift_case f n (c,ids,a) = (c,ids, f (n+(List.length ids)) a)

let ast_map_lift f n = function
  | MLlam (i,a) -> MLlam (i, f (n+1) a)
  | MLletin (i,a,b) -> MLletin (i, f n a, f (n+1) b)
  | MLcase (i,a,v) -> MLcase (i,f n a,Array.map (ast_map_lift_case f n) v)
  | MLfix (i,ids,v) ->
      let k = Array.length ids in MLfix (i,ids,Array.map (f (k+n)) v)
  | MLapp (a,l) -> MLapp (f n a, List.map (f n) l)
  | MLcons (i,c,l) -> MLcons (i,c, List.map (f n) l)
  | MLmagic a -> MLmagic (f n a)
  | MLrel _ | MLglob _ | MLexn _ | MLdummy | MLaxiom as a -> a

(*s Iter over asts. *)

let ast_iter_case f (_c,_ids,a) = f a

let ast_iter f = function
  | MLlam (_i,a) -> f a
  | MLletin (_i,a,b) -> f a; f b
  | MLcase (_,a,v) -> f a; Array.iter (ast_iter_case f) v
  | MLfix (_i,_ids,v) -> Array.iter f v
  | MLapp (a,l) -> f a; List.iter f l
  | MLcons (_,_c,l) -> List.iter f l
  | MLmagic a -> f a
  | MLrel _ | MLglob _ | MLexn _ | MLdummy | MLaxiom  -> ()

(*S Operations concerning De Bruijn indices. *)

(*s [ast_occurs k t] returns [true] if [(Rel k)] occurs in [t]. *)

let ast_occurs k t =
  try
    ast_iter_rel (fun i -> if i = k then raise Found) t; false
  with Found -> true

(*s [occurs_itvl k k' t] returns [true] if there is a [(Rel i)]
   in [t] with [k<=i<=k'] *)

let ast_occurs_itvl k k' t =
  try
    ast_iter_rel (fun i -> if (k <= i) && (i <= k') then raise Found) t; false
  with Found -> true

(*s Number of occurences of [Rel k] (resp. [Rel 1]) in [t]. *)

(*let nb_occur_k k t =
  let cpt = ref 0 in
  ast_iter_rel (fun i -> if i = k then incr cpt) t;
  !cpt*)

(*let nb_occur t = nb_occur_k 1 t*)

(* Number of occurences of [Rel 1] in [t], with special treatment of match:
   occurences in different branches aren't added, but we rather use max. *)

let nb_occur_match =
  let rec nb k = function
    | MLrel i -> if i = k then 1 else 0
    | MLcase(_,a,v) ->
        (nb k a) +
	Array.fold_left
	  (fun r (_,ids,a) -> max r (nb (k+(List.length ids)) a)) 0 v
    | MLletin (_,a,b) -> (nb k a) + (nb (k+1) b)
    | MLfix (_,ids,v) -> let k = k+(Array.length ids) in
      Array.fold_left (fun r a -> r+(nb k a)) 0 v
    | MLlam (_,a) -> nb (k+1) a
    | MLapp (a,l) -> List.fold_left (fun r a -> r+(nb k a)) (nb k a) l
    | MLcons (_,_,l) -> List.fold_left (fun r a -> r+(nb k a)) 0 l
    | MLmagic a -> nb k a
    | MLglob _ | MLexn _ | MLdummy | MLaxiom -> 0
  in nb 1

(*s Lifting on terms.
    [ast_lift k t] lifts the binding depth of [t] across [k] bindings. *)

let ast_lift k t =
  let rec liftrec n = function
    | MLrel i as a -> if i-n < 1 then a else MLrel (i+k)
    | a -> ast_map_lift liftrec n a
  in if k = 0 then t else liftrec 0 t

let ast_pop t = ast_lift (-1) t

(*s [permut_rels k k' c] translates [Rel 1 ... Rel k] to [Rel (k'+1) ...
  Rel (k'+k)] and [Rel (k+1) ... Rel (k+k')] to [Rel 1 ... Rel k'] *)

let permut_rels k k' =
  let rec permut n = function
    | MLrel i as a ->
	let i' = i-n in
	if i'<1 || i'>k+k' then a
	else if i'<=k then MLrel (i+k')
	else MLrel (i-k)
    | a -> ast_map_lift permut n a
  in permut 0

(*s Substitution. [ml_subst e t] substitutes [e] for [Rel 1] in [t].
    Lifting (of one binder) is done at the same time. *)

let ast_subst e =
  let rec subst n = function
    | MLrel i as a ->
	let i' = i-n in
	if i'=1 then ast_lift n e
	else if i'<1 then a
	else MLrel (i-1)
    | a -> ast_map_lift subst n a
  in subst 0

(*s Generalized substitution.
   [gen_subst v d t] applies to [t] the substitution coded in the
   [v] array: [(Rel i)] becomes [v.(i-1)]. [d] is the correction applies
   to [Rel] greater than [Array.length v]. *)

let gen_subst v d t =
  let rec subst n = function
    | MLrel i as a ->
	let i'= i-n in
	if i' < 1 then a
	else if i' <= Array.length v then
	  match v.(i'-1) with
	    | None -> MLexn ("UNBOUND " ^ string_of_int i')
	    | Some u -> ast_lift n u
	else MLrel (i+d)
    | a -> ast_map_lift subst n a
  in subst 0 t

(*S Operations concerning lambdas. *)

(*s [collect_lams MLlam(id1,...MLlam(idn,t)...)] returns
    [[idn;...;id1]] and the term [t]. *)

let collect_lams =
  let rec collect acc = function
    | MLlam(id,t) -> collect (id::acc) t
    | x           -> acc,x
  in collect []

(*s [collect_n_lams] does the same for a precise number of [MLlam]. *)

let collect_n_lams =
  let rec collect acc n t =
    if n = 0 then acc,t
    else match t with
      | MLlam(id,t) -> collect (id::acc) (n-1) t
      | _ -> assert false
  in collect []

(*s [remove_n_lams] just removes some [MLlam]. *)

let rec remove_n_lams n t =
  if n = 0 then t
  else match t with
      | MLlam(_,t) -> remove_n_lams (n-1) t
      | _ -> assert false

(*s [nb_lams] gives the number of head [MLlam]. *)

let rec nb_lams = function
  | MLlam(_,t) -> succ (nb_lams t)
  | _ -> 0

(*s [named_lams] does the converse of [collect_lams]. *)

let rec named_lams ids a = match ids with
  | [] -> a
  | id :: ids -> named_lams ids (MLlam (id,a))

(*s The same for a specific identifier (resp. anonymous, dummy) *)

let rec many_lams id a = function
  | 0 -> a
  | n -> many_lams id (MLlam (id,a)) (pred n)

(*let anonym_lams a n = many_lams anonymous a n*)
let anonym_tmp_lams a n = many_lams (Tmp anonymous_name) a n
let dummy_lams a n = many_lams Dummy a n

(*s mixed according to a signature. *)

let rec anonym_or_dummy_lams a = function
  | [] -> a
  | Keep :: s -> MLlam(anonymous, anonym_or_dummy_lams a s)
  | Kill _ :: s -> MLlam(Dummy, anonym_or_dummy_lams a s)

(*S Operations concerning eta. *)

(*s The following function creates [MLrel n;...;MLrel 1] *)

let rec eta_args n =
  if n = 0 then [] else (MLrel n)::(eta_args (pred n))

(*s Same, but filtered by a signature. *)

let rec eta_args_sign n = function
  | [] -> []
  | Keep :: s -> (MLrel n) :: (eta_args_sign (n-1) s)
  | Kill _ :: s -> eta_args_sign (n-1) s

(*s This one tests [MLrel (n+k); ... ;MLrel (1+k)] *)

let rec test_eta_args_lift k n = function
  | [] -> n=0
  | a :: q -> (a = (MLrel (k+n))) && (test_eta_args_lift k (pred n) q)

(*s Computes an eta-reduction. *)

(*let eta_red e =
  let ids,t = collect_lams e in
  let n = List.length ids in
  if n = 0 then e
  else match t with
    | MLapp (f,a) ->
	let m = List.length a in
	let ids,body,args =
	  if m = n then
	    [], f, a
	  else if m < n then
	    list_skipn m ids, f, a
	  else (* m > n *)
	    let a1,a2 = list_chop (m-n) a in
	    [], MLapp (f,a1), a2
	in
	let p = List.length args in
	if test_eta_args_lift 0 p args && not (ast_occurs_itvl 1 p body)
	then named_lams ids (ast_lift (-p) body)
	else e
    | _ -> e*)

(*s Computes all head linear beta-reductions possible in [(t a)].
  Non-linear head beta-redex become let-in. *)

(*let rec linear_beta_red a t = match a,t with
  | [], _ -> t
  | a0::a, MLlam (id,t) ->
      (match nb_occur_match t with
	 | 0 -> linear_beta_red a (ast_pop t)
	 | 1 -> linear_beta_red a (ast_subst a0 t)
	 | _ ->
	     let a = List.map (ast_lift 1) a in
	     MLletin (id, a0, linear_beta_red a t))
  | _ -> MLapp (t, a)*)

(*let rec tmp_head_lams = function
  | MLlam (id, t) -> MLlam (tmp_id id, tmp_head_lams t)
  | e -> e*)

(*s Applies a substitution [s] of constants by their body, plus
  linear beta reductions at modified positions.
  Moreover, we mark some lambdas as suitable for later linear
  reduction (this helps the inlining of recursors).
*)

let ast_glob_subst _s _t = assert false (*CSC: reimplement match t with
  | MLapp ((MLglob ((ConstRef kn) as refe)) as f, a) ->
      let a = List.map (fun e -> tmp_head_lams (ast_glob_subst s e)) a in
      (try linear_beta_red a (Refmap'.find refe s)
       with Not_found -> MLapp (f, a))
  | MLglob ((ConstRef kn) as refe) ->
      (try Refmap'.find refe s with Not_found -> t)
  | _ -> ast_map (ast_glob_subst s) t *)


(*S Auxiliary functions used in simplification of ML cases. *)

(* Factorisation of some match branches into a common "x -> f x"
   branch may break types sometimes. Example: [type 'x a = A].
   Then [let id = function A -> A] has type ['x a -> 'y a],
   which is incompatible with the type of [let id x = x].
   We now check that the type arguments of the inductive are
   preserved by our transformation.

   TODO: this verification should be done someday modulo
   expansion of type definitions.
*)

(*s [branch_as_function b typs (r,l,c)] tries to see branch [c]
  as a function [f] applied to [MLcons(r,l)]. For that it transforms
  any [MLcons(r,l)] in [MLrel 1] and raises [Impossible]
  if any variable in [l] occurs outside such a [MLcons] *)

let branch_as_fun typs (r,l,c) =
  let nargs = List.length l in
  let rec genrec n = function
    | MLrel i as c ->
	let i' = i-n in
	if i'<1 then c
	else if i'>nargs then MLrel (i-nargs+1)
	else raise Impossible
    | MLcons(i,r',args) when
	r=r' && (test_eta_args_lift n nargs args) && typs = i.c_typs ->
	MLrel (n+1)
    | a -> ast_map_lift genrec n a
  in genrec 0 c

(*s [branch_as_cst (r,l,c)] tries to see branch [c] as a constant
   independent from the pattern [MLcons(r,l)]. For that is raises [Impossible]
   if any variable in [l] occurs in [c], and otherwise returns [c] lifted to
   appear like a function with one arg (for uniformity with [branch_as_fun]).
   NB: [MLcons(r,l)] might occur nonetheless in [c], but only when [l] is
   empty, i.e. when [r] is a constant constructor
*)

let branch_as_cst (_,l,c) =
  let n = List.length l in
  if ast_occurs_itvl 1 n c then raise Impossible;
  ast_lift (1-n) c

(* A branch [MLcons(r,l)->c] can be seen at the same time as a function
   branch and a constant branch, either because:
   - [MLcons(r,l)] doesn't occur in [c]. For example : "A -> B"
   - this constructor is constant (i.e. [l] is empty). For example "A -> A"
   When searching for the best factorisation below, we'll try both.
*)

(* The following structure allows to record which element occurred
   at what position, and then finally return the most frequent
   element and its positions. *)

let census_add, census_max, census_clean =
  let h = Hashtbl.create 13 in
  let clear () = Hashtbl.clear h in
  let add e i =
    let s = try Hashtbl.find h e with Not_found -> Intset.empty in
    Hashtbl.replace h e (Intset.add i s)
  in
  let max e0 =
    let len = ref 0 and lst = ref Intset.empty and elm = ref e0 in
    Hashtbl.iter
      (fun e s ->
	 let n = Intset.cardinal s in
	 if n > !len then begin len := n; lst := s; elm := e end)
      h;
    (!elm,!lst)
  in
  (add,max,clear)

(* [factor_branches] return the longest possible list of branches
   that have the same factorization, either as a function or as a
   constant.
*)

let factor_branches o typs br =
  census_clean ();
  for i = 0 to Array.length br - 1 do
    if o.opt_case_idr then
      (try census_add (branch_as_fun typs br.(i)) i with Impossible -> ());
    if o.opt_case_cst then
      (try census_add (branch_as_cst br.(i)) i with Impossible -> ());
  done;
  let br_factor, br_set = census_max MLdummy in
  census_clean ();
  let n = Intset.cardinal br_set in
  if n = 0 then None
  else if Array.length br >= 2 && n < 2 then None
  else Some (br_factor, br_set)

(*s If all branches are functions, try to permut the case and the functions. *)

let rec merge_ids ids ids' = match ids,ids' with
  | [],l -> l
  | l,[] -> l
  | i::ids, i'::ids' ->
      (if i = Dummy then i' else i) :: (merge_ids ids ids')

let is_exn = function MLexn _ -> true | _ -> false

let permut_case_fun br _acc =
  let nb = ref max_int in
  Array.iter (fun (_,_,t) ->
		let ids, c = collect_lams t in
		let n = List.length ids in
		if (n < !nb) && (not (is_exn c)) then nb := n) br;
  if !nb = max_int || !nb = 0 then ([],br)
  else begin
    let br = Array.copy br in
    let ids = ref [] in
    for i = 0 to Array.length br - 1 do
      let (r,l,t) = br.(i) in
      let local_nb = nb_lams t in
      if local_nb < !nb then (* t = MLexn ... *)
	br.(i) <- (r,l,remove_n_lams local_nb t)
      else begin
	let local_ids,t = collect_n_lams !nb t in
	ids := merge_ids !ids local_ids;
	br.(i) <- (r,l,permut_rels !nb (List.length l) t)
      end
    done;
    (!ids,br)
  end

(*S Generalized iota-reduction. *)

(* Definition of a generalized iota-redex: it's a [MLcase(e,_)]
   with [(is_iota_gen e)=true]. Any generalized iota-redex is
   transformed into beta-redexes. *)

let rec is_iota_gen = function
  | MLcons _ -> true
  | MLcase(_,_,br)-> array_for_all (fun (_,_,t)->is_iota_gen t) br
  | _ -> false

let constructor_index _ = assert false (*CSC: function
  | ConstructRef (_,j) -> pred j
  | _ -> assert false*)

let iota_gen br =
  let rec iota k = function
    | MLcons (_i,r,a) ->
	let (_,ids,c) = br.(constructor_index r) in
	let c = List.fold_right (fun id t -> MLlam (id,t)) ids c in
	let c = ast_lift k c in
	MLapp (c,a)
    | MLcase(i,e,br') ->
	let new_br =
	  Array.map (fun (n,i,c)->(n,i,iota (k+(List.length i)) c)) br'
	in MLcase(i,e, new_br)
    | _ -> assert false
  in iota 0

let is_atomic = function
  | MLrel _ | MLglob _ | MLexn _ | MLdummy -> true
  | _ -> false

let is_imm_apply = function MLapp (MLrel 1, _) -> true | _ -> false

(** Program creates a let-in named "program_branch_NN" for each branch of match.
    Unfolding them leads to more natural code (and more dummy removal) *)

let is_program_branch = function
  | Id id ->
    let s = id in
    let br = "program_branch_" in
    let n = String.length br in
    (try
       ignore (int_of_string (String.sub s n (String.length s - n)));
       String.sub s 0 n = br
     with _ -> false)
  | Tmp _ | Dummy -> false

let expand_linear_let o id e =
   o.opt_lin_let || is_tmp id || is_program_branch id || is_imm_apply e

(*S The main simplification function. *)

(* Some beta-iota reductions + simplifications. *)

let rec simpl o = function
  | MLapp (f, []) -> simpl o f
  | MLapp (f, a) -> simpl_app o (List.map (simpl o) a) (simpl o f)
  | MLcase (i,e,br) ->
      let br = Array.map (fun (n,l,t) -> (n,l,simpl o t)) br in
      simpl_case o i br (simpl o e)
  | MLletin(Dummy,_,e) -> simpl o (ast_pop e)
  | MLletin(id,c,e) ->
      let e = simpl o e in
      if
	(is_atomic c) || (is_atomic e) ||
	(let n = nb_occur_match e in
	 (n = 0 || (n=1 && expand_linear_let o id e)))
      then
	simpl o (ast_subst c e)
      else
	MLletin(id, simpl o c, e)
  | MLfix(i,ids,c) ->
      let n = Array.length ids in
      if ast_occurs_itvl 1 n c.(i) then
	MLfix (i, ids, Array.map (simpl o) c)
      else simpl o (ast_lift (-n) c.(i)) (* Dummy fixpoint *)
  | a -> ast_map (simpl o) a

(* invariant : list [a] of arguments is non-empty *)

and simpl_app o a = function
  | MLapp (f',a') -> simpl_app o (a'@a) f'
  | MLlam (Dummy,t) ->
      simpl o (MLapp (ast_pop t, List.tl a))
  | MLlam (id,t) -> (* Beta redex *)
      (match nb_occur_match t with
	 | 0 -> simpl o (MLapp (ast_pop t, List.tl a))
	 | 1 when (is_tmp id || o.opt_lin_beta) ->
	     simpl o (MLapp (ast_subst (List.hd a) t, List.tl a))
	 | _ ->
	     let a' = List.map (ast_lift 1) (List.tl a) in
	     simpl o (MLletin (id, List.hd a, MLapp (t, a'))))
  | MLletin (id,e1,e2) when o.opt_let_app ->
      (* Application of a letin: we push arguments inside *)
      MLletin (id, e1, simpl o (MLapp (e2, List.map (ast_lift 1) a)))
  | MLcase (i,e,br) when o.opt_case_app ->
      (* Application of a case: we push arguments inside *)
      let br' =
	Array.map
      	  (fun (n,l,t) ->
	     let k = List.length l in
	     let a' = List.map (ast_lift k) a in
      	     (n, l, simpl o (MLapp (t,a')))) br
      in simpl o (MLcase (i,e,br'))
  | (MLdummy | MLexn _) as e -> e
	(* We just discard arguments in those cases. *)
  | f -> MLapp (f,a)

(* Invariant : all empty matches should now be [MLexn] *)

and simpl_case o i br e =
  if o.opt_case_iot && (is_iota_gen e) then (* Generalized iota-redex *)
    simpl o (iota_gen br e)
  else
    (* Swap the case and the lam if possible *)
    let ids,br = if o.opt_case_fun then permut_case_fun br [] else [],br in
    let n = List.length ids in
    if n <> 0 then
      simpl o (named_lams ids (MLcase (i,ast_lift n e, br)))
    else
      (* Can we merge several branches as the same constant or function ? *)
      match factor_branches o i.m_typs br with
	| Some (f,ints) when Intset.cardinal ints = Array.length br ->
	    (* If all branches have been factorized, we remove the match *)
	    simpl o (MLletin (Tmp anonymous_name, e, f))
	| Some (f,ints) ->
	  let same = if ast_occurs 1 f then BranchFun ints else BranchCst ints
	  in MLcase ({i with m_same=same}, e, br)
	| None -> MLcase (i, e, br)

(*S Local prop elimination. *)
(* We try to eliminate as many [prop] as possible inside an [ml_ast]. *)

(*s In a list, it selects only the elements corresponding to a [Keep]
   in the boolean list [l]. *)

let rec select_via_bl l args = match l,args with
  | [],_ -> args
  | Keep::l,a::args -> a :: (select_via_bl l args)
  | Kill _::l,_a::args -> select_via_bl l args
  | _ -> assert false

(*s [kill_some_lams] removes some head lambdas according to the signature [bl].
   This list is build on the identifier list model: outermost lambda
   is on the right.
   [Rels] corresponding to removed lambdas are supposed not to occur, and
   the other [Rels] are made correct via a [gen_subst].
   Output is not directly a [ml_ast], compose with [named_lams] if needed. *)

let kill_some_lams bl (ids,c) =
  let n = List.length bl in
  let n' = List.fold_left (fun n b -> if b=Keep then (n+1) else n) 0 bl in
  if n = n' then ids,c
  else if n' = 0 then [],ast_lift (-n) c
  else begin
    let v = Array.make n None in
    let rec parse_ids i j = function
      | [] -> ()
      | Keep :: l -> v.(i) <- Some (MLrel j); parse_ids (i+1) (j+1) l
      | Kill _ :: l -> parse_ids (i+1) j l
    in parse_ids 0 1 bl;
    select_via_bl bl ids, gen_subst v (n'-n) c
  end

(*s [kill_dummy_lams] uses the last function to kill the lambdas corresponding
  to a [dummy_name]. It can raise [Impossible] if there is nothing to do, or
  if there is no lambda left at all. *)

let kill_dummy_lams c =
  let ids,c = collect_lams c in
  let bl = List.map sign_of_id ids in
  if not (List.mem Keep bl) then raise Impossible;
  let rec fst_kill n = function
    | [] -> raise Impossible
    | Kill _ :: _bl -> n
    | Keep :: bl -> fst_kill (n+1) bl
  in
  let skip = max 0 ((fst_kill 0 bl) - 1) in
  let ids_skip, ids = list_chop skip ids in
  let _, bl = list_chop skip bl in
  let c = named_lams ids_skip c in
  let ids',c = kill_some_lams bl (ids,c) in
  ids, named_lams ids' c

(*s [eta_expansion_sign] takes a function [fun idn ... id1 -> c]
   and a signature [s] and builds a eta-long version. *)

(* For example, if [s = [Keep;Keep;Kill Prop;Keep]] then the output is :
   [fun idn ... id1 x x _ x -> (c' 4 3 __ 1)]  with [c' = lift 4 c] *)

let eta_expansion_sign s (ids,c) =
  let rec abs ids rels i = function
    | [] ->
	let a = List.rev_map (function MLrel x -> MLrel (i-x) | a -> a) rels
	in ids, MLapp (ast_lift (i-1) c, a)
    | Keep :: l -> abs (anonymous :: ids) (MLrel i :: rels) (i+1) l
    | Kill _ :: l -> abs (Dummy :: ids) (MLdummy :: rels) (i+1) l
  in abs ids [] 1 s

(*s If [s = [b1; ... ; bn]] then [case_expunge] decomposes [e]
  in [n] lambdas (with eta-expansion if needed) and removes all dummy lambdas
  corresponding to [Del] in [s]. *)

let case_expunge s e =
  let m = List.length s in
  let n = nb_lams e in
  let p = if m <= n then collect_n_lams m e
  else eta_expansion_sign (list_skipn n s) (collect_lams e) in
  kill_some_lams (List.rev s) p

(*s [term_expunge] takes a function [fun idn ... id1 -> c]
  and a signature [s] and remove dummy lams. The difference
  with [case_expunge] is that we here leave one dummy lambda
  if all lambdas are logical dummy and the target language is strict. *)

let term_expunge s (ids,c) =
  if s = [] then c
  else
    let ids,c = kill_some_lams (List.rev s) (ids,c) in
    if ids = [] && List.mem (Kill Kother) s then
      MLlam (Dummy, ast_lift 1 c)
    else named_lams ids c

(*s [kill_dummy_args ids r t] looks for occurences of [MLrel r] in [t] and
  purge the args of [MLrel r] corresponding to a [dummy_name].
  It makes eta-expansion if needed. *)

let kill_dummy_args ids r t =
  let m = List.length ids in
  let bl = List.rev_map sign_of_id ids in
  let rec found n = function
    | MLrel r' when r' = r + n -> true
    | MLmagic e -> found n e
    | _ -> false
  in
  let rec killrec n = function
    | MLapp(e, a) when found n e ->
	let k = max 0 (m - (List.length a)) in
	let a = List.map (killrec n) a in
	let a = List.map (ast_lift k) a in
	let a = select_via_bl bl (a @ (eta_args k)) in
	named_lams (list_firstn k ids) (MLapp (ast_lift k e, a))
    | e when found n e ->
	let a = select_via_bl bl (eta_args m) in
	named_lams ids (MLapp (ast_lift m e, a))
    | e -> ast_map_lift killrec n e
  in killrec 0 t

(*s The main function for local [dummy] elimination. *)

let rec kill_dummy = function
  | MLfix(i,fi,c) ->
      (try
	 let ids,c = kill_dummy_fix i c in
	 ast_subst (MLfix (i,fi,c)) (kill_dummy_args ids 1 (MLrel 1))
       with Impossible -> MLfix (i,fi,Array.map kill_dummy c))
  | MLapp (MLfix (i,fi,c),a) ->
      let a = List.map kill_dummy a in
      (try
	 let ids,c = kill_dummy_fix i c in
	 let fake = MLapp (MLrel 1, List.map (ast_lift 1) a) in
	 let fake' = kill_dummy_args ids 1 fake in
	 ast_subst (MLfix (i,fi,c)) fake'
       with Impossible -> MLapp(MLfix(i,fi,Array.map kill_dummy c),a))
  | MLletin(id, MLfix (i,fi,c),e) ->
      (try
	 let ids,c = kill_dummy_fix i c in
	 let e = kill_dummy (kill_dummy_args ids 1 e) in
	 MLletin(id, MLfix(i,fi,c),e)
      with Impossible ->
	MLletin(id, MLfix(i,fi,Array.map kill_dummy c),kill_dummy e))
  | MLletin(id,c,e) ->
      (try
	 let ids,c = kill_dummy_lams (kill_dummy_hd c) in
	 let e = kill_dummy (kill_dummy_args ids 1 e) in
	 let c = kill_dummy c in
	 if is_atomic c then ast_subst c e else MLletin (id, c, e)
       with Impossible -> MLletin(id,kill_dummy c,kill_dummy e))
  | a -> ast_map kill_dummy a

(* Similar function, but acting only on head lambdas and let-ins *)

and kill_dummy_hd = function
  | MLlam(id,e) -> MLlam(id, kill_dummy_hd e)
  | MLletin(id,c,e) ->
      (try
	 let ids,c = kill_dummy_lams (kill_dummy_hd c) in
	 let e = kill_dummy_hd (kill_dummy_args ids 1 e) in
	 let c = kill_dummy c in
	 if is_atomic c then ast_subst c e else MLletin (id, c, e)
       with Impossible -> MLletin(id,kill_dummy c,kill_dummy_hd e))
  | a -> a

and kill_dummy_fix i c =
  let n = Array.length c in
  let ids,ci = kill_dummy_lams (kill_dummy_hd c.(i)) in
  let c = Array.copy c in c.(i) <- ci;
  for j = 0 to (n-1) do
    c.(j) <- kill_dummy (kill_dummy_args ids (n-i) c.(j))
  done;
  ids,c

(*s Putting things together. *)

let normalize a =
  let o = optims () in
  let rec norm a =
    let a' = if o.opt_kill_dum then kill_dummy (simpl o a) else simpl o a in
    if a = a' then a else norm a'
  in norm a

(*S Special treatment of fixpoint for pretty-printing purpose. *)

let general_optimize_fix f ids n args m c =
  let v = Array.make n 0 in
  for i=0 to (n-1) do v.(i)<-i done;
  let aux i = function
    | MLrel j when v.(j-1)>=0 ->
	if ast_occurs (j+1) c then raise Impossible else v.(j-1)<-(-i-1)
    | _ -> raise Impossible
  in list_iter_i aux args;
  let args_f = List.rev_map (fun i -> MLrel (i+m+1)) (Array.to_list v) in
  let new_f = anonym_tmp_lams (MLapp (MLrel (n+m+1),args_f)) m in
  let new_c = named_lams ids (normalize (MLapp ((ast_subst new_f c),args))) in
  MLfix(0,[|f|],[|new_c|])

let optimize_fix a =
  if not (optims()).opt_fix_fun then a
  else
    let ids,a' = collect_lams a in
    let n = List.length ids in
    if n = 0 then a
    else match a' with
      | MLfix(_,[|f|],[|c|]) ->
	  let new_f = MLapp (MLrel (n+1),eta_args n) in
	  let new_c = named_lams ids (normalize (ast_subst new_f c))
	  in MLfix(0,[|f|],[|new_c|])
      | MLapp(a',args) ->
	  let m = List.length args in
	  (match a' with
	     | MLfix(_,_,_) when
		 (test_eta_args_lift 0 n args) && not (ast_occurs_itvl 1 m a')
		 -> a'
	     | MLfix(_,[|f|],[|c|]) ->
		 (try general_optimize_fix f ids n args m c
		  with Impossible -> a)
	     | _ -> a)
      | _ -> a

(*S Inlining. *)

(* Utility functions used in the decision of inlining. *)

(*let rec ml_size = function
  | MLapp(t,l) -> List.length l + ml_size t + ml_size_list l
  | MLlam(_,t) -> 1 + ml_size t
  | MLcons(_,_,l) -> ml_size_list l
  | MLcase(_,t,pv) ->
      1 + ml_size t + (Array.fold_right (fun (_,_,t) a -> a + ml_size t) pv 0)
  | MLfix(_,_,f) -> ml_size_array f
  | MLletin (_,_,t) -> ml_size t
  | MLmagic t -> ml_size t
  | _ -> 0

and ml_size_list l = List.fold_left (fun a t -> a + ml_size t) 0 l

and ml_size_array l = Array.fold_left (fun a t -> a + ml_size t) 0 l*)

(*let is_fix = function MLfix _ -> true | _ -> false*)

(*let rec is_constr = function
  | MLcons _   -> true
  | MLlam(_,t) -> is_constr t
  | _          -> false*)

(*s Strictness *)

(* A variable is strict if the evaluation of the whole term implies
   the evaluation of this variable. Non-strict variables can be found
   behind Match, for example. Expanding a term [t] is a good idea when
   it begins by at least one non-strict lambda, since the corresponding
   argument to [t] might be unevaluated in the expanded code. *)

(*exception Toplevel*)

(*let lift n l = List.map ((+) n) l*)

(*let pop n l = List.map (fun x -> if x<=n then raise Toplevel else x-n) l*)

(* This function returns a list of de Bruijn indices of non-strict variables,
   or raises [Toplevel] if it has an internal non-strict variable.
   In fact, not all variables are checked for strictness, only the ones which
   de Bruijn index is in the candidates list [cand]. The flag [add] controls
   the behaviour when going through a lambda: should we add the corresponding
   variable to the candidates?  We use this flag to check only the external
   lambdas, those that will correspond to arguments. *)

(*let rec non_stricts add cand = function
  | MLlam (_id,t) ->
      let cand = lift 1 cand in
      let cand = if add then 1::cand else cand in
      pop 1 (non_stricts add cand t)
  | MLrel n ->
      List.filter ((<>) n) cand
  | MLapp (t,l)->
      let cand = non_stricts false cand t in
      List.fold_left (non_stricts false) cand l
  | MLcons (_,_,l) ->
      List.fold_left (non_stricts false) cand l
  | MLletin (_,t1,t2) ->
      let cand = non_stricts false cand t1 in
      pop 1 (non_stricts add (lift 1 cand) t2)
  | MLfix (_,i,f)->
      let n = Array.length i in
      let cand = lift n cand in
      let cand = Array.fold_left (non_stricts false) cand f in
      pop n cand
  | MLcase (_,t,v) ->
      (* The only interesting case: for a variable to be non-strict, *)
      (* it is sufficient that it appears non-strict in at least one branch, *)
      (* so we make an union (in fact a merge). *)
      let cand = non_stricts false cand t in
      Array.fold_left
	(fun c (_,i,t)->
	   let n = List.length i in
	   let cand = lift n cand in
	   let cand = pop n (non_stricts add cand t) in
	   List.merge (-) cand c) [] v
	(* [merge] may duplicates some indices, but I don't mind. *)
  | MLmagic t ->
      non_stricts add cand t
  | _ ->
      cand*)

(* The real test: we are looking for internal non-strict variables, so we start
   with no candidates, and the only positive answer is via the [Toplevel]
   exception. *)

(*let is_not_strict t =
  try let _ = non_stricts true [] t in false
  with Toplevel -> true*)

(*s Inlining decision *)

(* [inline_test] answers the following question:
   If we could inline [t] (the user said nothing special),
   should we inline ?

   We expand small terms with at least one non-strict
   variable (i.e. a variable that may not be evaluated).

   Futhermore we don't expand fixpoints.

   Moreover, as mentionned by X. Leroy (bug #2241),
   inling a constant from inside an opaque module might
   break types. To avoid that, we require below that
   both [r] and its body are globally visible. This isn't
   fully satisfactory, since [r] might not be visible (functor),
   and anyway it might be interesting to inline [r] at least
   inside its own structure. But to be safe, we adopt this
   restriction for the moment.
*)

(*let inline_test _r _t =
  (*CSC:if not (auto_inline ()) then*) false
(*
  else
    let c = match r with ConstRef c -> c | _ -> assert false in
    let body = try (Global.lookup_constant c).const_body with _ -> None in
    if body = None then false
    else
      let t1 = eta_red t in
      let t2 = snd (collect_lams t1) in
      not (is_fix t2) && ml_size t < 12 && is_not_strict t
*)*)

(*CSC: (not) reimplemented
let con_of_string s =
  let null = empty_dirpath in
  match repr_dirpath (dirpath_of_string s) with
    | id :: d -> make_con (MPfile (make_dirpath d)) null (label_of_id id)
    | [] -> assert false

let manual_inline_set =
  List.fold_right (fun x -> Cset_env.add (con_of_string x))
    [ "Coq.Init.Wf.well_founded_induction_type";
      "Coq.Init.Wf.well_founded_induction";
      "Coq.Init.Wf.Acc_iter";
      "Coq.Init.Wf.Fix_F";
      "Coq.Init.Wf.Fix";
      "Coq.Init.Datatypes.andb";
      "Coq.Init.Datatypes.orb";
      "Coq.Init.Logic.eq_rec_r";
      "Coq.Init.Logic.eq_rect_r";
      "Coq.Init.Specif.proj1_sig";
    ]
    Cset_env.empty*)

(*let manual_inline = function (*CSC:
  | ConstRef c -> Cset_env.mem c manual_inline_set
  |*) _ -> false*)

(* If the user doesn't say he wants to keep [t], we inline in two cases:
   \begin{itemize}
   \item the user explicitly requests it
   \item [expansion_test] answers that the inlining is a good idea, and
   we are free to act (AutoInline is set)
   \end{itemize} *)

let inline _r _t = false (*CSC: we never inline atm
  (*CSC:not (to_keep r) (* The user DOES want to keep it *)
  && not (is_inline_custom r)
  &&*) (false(*to_inline r*) (* The user DOES want to inline it *)
     || (not (is_projection r) &&
         (is_recursor r || manual_inline r || inline_test r t)))
*)