(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2016     *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(* Created in Caml by Gérard Huet for CoC 4.8 [Dec 1988] *)
(* Functional code by Jean-Christophe Filliâtre for Coq V7.0 [1999] *)
(* Extension with algebraic universes by HH for Coq V7.0 [Sep 2001] *)
(* Additional support for sort-polymorphic inductive types by HH [Mar 2006] *)
(* Support for universe polymorphism by MS [2014] *)

(* Revisions by Bruno Barras, Hugo Herbelin, Pierre Letouzey, Matthieu
   Sozeau, Pierre-Marie Pédrot *)

open Pp
open CErrors
open Util

(* Universes are stratified by a partial ordering $\le$.
   Let $\~{}$ be the associated equivalence. We also have a strict ordering
   $<$ between equivalence classes, and we maintain that $<$ is acyclic,
   and contained in $\le$ in the sense that $[U]<[V]$ implies $U\le V$.

   At every moment, we have a finite number of universes, and we
   maintain the ordering in the presence of assertions $U<V$ and $U\le V$.

   The equivalence $\~{}$ is represented by a tree structure, as in the
   union-find algorithm. The assertions $<$ and $\le$ are represented by
   adjacency lists *)

module type Hashconsed =
sig
  type t
  val hash : t -> int
  val eq : t -> t -> bool
  val hcons : t -> t
end

module HashedList (M : Hashconsed) :
sig
  type t = private Nil | Cons of M.t * int * t
  val nil : t
  val cons : M.t -> t -> t
end =
struct
  type t = Nil | Cons of M.t * int * t
  module Self =
  struct
    type _t = t
    type t = _t
    type u = (M.t -> M.t)
    let hash = function Nil -> 0 | Cons (_, h, _) -> h
    let eq l1 l2 = match l1, l2 with
    | Nil, Nil -> true
    | Cons (x1, _, l1), Cons (x2, _, l2) -> x1 == x2 && l1 == l2
    | _ -> false
    let hashcons hc = function
    | Nil -> Nil
    | Cons (x, h, l) -> Cons (hc x, h, l)
  end
  module Hcons = Hashcons.Make(Self)
  let hcons = Hashcons.simple_hcons Hcons.generate Hcons.hcons M.hcons
  (** No recursive call: the interface guarantees that all HLists from this
      program are already hashconsed. If we get some external HList, we can
      still reconstruct it by traversing it entirely. *)
  let nil = Nil
  let cons x l =
    let h = M.hash x in
    let hl = match l with Nil -> 0 | Cons (_, h, _) -> h in
    let h = Hashset.Combine.combine h hl in
    hcons (Cons (x, h, l))
end

module HList = struct

  module type S = sig
    type elt
    type t = private Nil | Cons of elt * int * t
    val hash : t -> int
    val nil : t
    val cons : elt -> t -> t
    val tip : elt -> t
    val fold : (elt -> 'a -> 'a) -> t -> 'a -> 'a
    val map : (elt -> elt) -> t -> t
    val smartmap : (elt -> elt) -> t -> t
    val exists : (elt -> bool) -> t -> bool
    val for_all : (elt -> bool) -> t -> bool
    val for_all2 : (elt -> elt -> bool) -> t -> t -> bool
    val mem : elt -> t -> bool
    val remove : elt -> t -> t
    val to_list : t -> elt list
    val compare : (elt -> elt -> int) -> t -> t -> int
  end

  module Make (H : Hashconsed) : S with type elt = H.t =
  struct
  type elt = H.t
  include HashedList(H)

  let hash = function Nil -> 0 | Cons (_, h, _) -> h

  let tip e = cons e nil

  let rec fold f l accu = match l with
  | Nil -> accu
  | Cons (x, _, l) -> fold f l (f x accu)

  let rec map f = function
  | Nil -> nil
  | Cons (x, _, l) -> cons (f x) (map f l)

  let smartmap = map
  (** Apriori hashconsing ensures that the map is equal to its argument *)

  let rec exists f = function
  | Nil -> false
  | Cons (x, _, l) -> f x || exists f l

  let rec for_all f = function
  | Nil -> true
  | Cons (x, _, l) -> f x && for_all f l

  let rec for_all2 f l1 l2 = match l1, l2 with
  | Nil, Nil -> true
  | Cons (x1, _, l1), Cons (x2, _, l2) -> f x1 x2 && for_all2 f l1 l2
  | _ -> false

  let rec to_list = function
  | Nil -> []
  | Cons (x, _, l) -> x :: to_list l

  let rec remove x = function
  | Nil -> nil
  | Cons (y, _, l) ->
    if H.eq x y then l
    else cons y (remove x l)

  let rec mem x = function
  | Nil -> false
  | Cons (y, _, l) -> H.eq x y || mem x l

  let rec compare cmp l1 l2 = match l1, l2 with
  | Nil, Nil -> 0
  | Cons (x1, h1, l1), Cons (x2, h2, l2) ->
    let c = Int.compare h1 h2 in
    if c == 0 then
      let c = cmp x1 x2 in
      if c == 0 then
        compare cmp l1 l2
      else c
    else c
  | Cons _, Nil -> 1
  | Nil, Cons _ -> -1

  end
end

module RawLevel =
struct
  open Names
  type t =
    | Prop
    | Set
    | Level of int * DirPath.t
    | Var of int

  (* Hash-consing *)

  let equal x y =
    x == y ||
      match x, y with
      | Prop, Prop -> true
      | Set, Set -> true
      | Level (n,d), Level (n',d') ->
        Int.equal n n' && DirPath.equal d d'
      | Var n, Var n' -> Int.equal n n'
      | _ -> false

  let compare u v =
    match u, v with
    | Prop,Prop -> 0
    | Prop, _ -> -1
    | _, Prop -> 1
    | Set, Set -> 0
    | Set, _ -> -1
    | _, Set -> 1
    | Level (i1, dp1), Level (i2, dp2) ->
      if i1 < i2 then -1
      else if i1 > i2 then 1
      else DirPath.compare dp1 dp2
    | Level _, _ -> -1
    | _, Level _ -> 1
    | Var n, Var m -> Int.compare n m

  let hequal x y =
    x == y ||
      match x, y with
      | Prop, Prop -> true
      | Set, Set -> true
      | Level (n,d), Level (n',d') ->
        n == n' && d == d'
      | Var n, Var n' -> n == n'
      | _ -> false

  let hcons = function
    | Prop as x -> x
    | Set as x -> x
    | Level (n,d) as x -> 
      let d' = Names.DirPath.hcons d in
        if d' == d then x else Level (n,d')
    | Var n as x -> x

  open Hashset.Combine

  let hash = function
    | Prop -> combinesmall 1 0
    | Set -> combinesmall 1 1
    | Var n -> combinesmall 2 n
    | Level (n, d) -> combinesmall 3 (combine n (Names.DirPath.hash d))

end

module Level = struct

  open Names

  type raw_level = RawLevel.t =
  | Prop
  | Set
  | Level of int * DirPath.t
  | Var of int

  (** Embed levels with their hash value *)
  type t = { 
    hash : int;
    data : RawLevel.t }

  let equal x y = 
    x == y || Int.equal x.hash y.hash && RawLevel.equal x.data y.data

  let hash x = x.hash

  let data x = x.data

  (** Hashcons on levels + their hash *)

  module Self = struct
    type _t = t
    type t = _t
    type u = unit
    let eq x y = x.hash == y.hash && RawLevel.hequal x.data y.data
    let hash x = x.hash
    let hashcons () x =
      let data' = RawLevel.hcons x.data in
      if x.data == data' then x else { x with data = data' }
  end

  let hcons =
    let module H = Hashcons.Make(Self) in
    Hashcons.simple_hcons H.generate H.hcons ()

  let make l = hcons { hash = RawLevel.hash l; data = l }

  let set = make Set
  let prop = make Prop

  let is_small x = 
    match data x with
    | Level _ -> false
    | Var _ -> false
    | Prop -> true
    | Set -> true
 
  let is_prop x =
    match data x with
    | Prop -> true
    | _ -> false

  let is_set x =
    match data x with
    | Set -> true
    | _ -> false

  let compare u v =
    if u == v then 0
    else
      let c = Int.compare (hash u) (hash v) in
	if c == 0 then RawLevel.compare (data u) (data v)
	else c

  let natural_compare u v =
    if u == v then 0
    else RawLevel.compare (data u) (data v)
	    
  let to_string x = 
    match data x with
    | Prop -> "Prop"
    | Set -> "Set"
    | Level (n,d) -> Names.DirPath.to_string d^"."^string_of_int n
    | Var n -> "Var(" ^ string_of_int n ^ ")"

  let pr u = str (to_string u)

  let apart u v =
    match data u, data v with
    | Prop, Set | Set, Prop -> true
    | _ -> false

  let vars = Array.init 20 (fun i -> make (Var i))

  let var n = 
    if n < 20 then vars.(n) else make (Var n)

  let var_index u =
    match data u with
    | Var n -> Some n | _ -> None

  let make m n = make (Level (n, Names.DirPath.hcons m))

end

(** Level maps *)
module LMap = struct 
  module M = HMap.Make (Level)
  include M

  let union l r = 
    merge (fun k l r -> 
      match l, r with
      | Some _, _ -> l
      | _, _ -> r) l r

  let subst_union l r = 
    merge (fun k l r -> 
      match l, r with
      | Some (Some _), _ -> l
      | Some None, None -> l
      | _, _ -> r) l r

  let diff ext orig =
    fold (fun u v acc -> 
      if mem u orig then acc 
      else add u v acc)
      ext empty

  let pr f m =
    h 0 (prlist_with_sep fnl (fun (u, v) ->
      Level.pr u ++ f v) (bindings m))
end

module LSet = struct
  include LMap.Set

  let pr prl s =
    str"{" ++ prlist_with_sep spc prl (elements s) ++ str"}"

  let of_array l =
    Array.fold_left (fun acc x -> add x acc) empty l

end


type 'a universe_map = 'a LMap.t

type universe_level = Level.t

type universe_level_subst_fn = universe_level -> universe_level

type universe_set = LSet.t

(* An algebraic universe [universe] is either a universe variable
   [Level.t] or a formal universe known to be greater than some
   universe variables and strictly greater than some (other) universe
   variables

   Universes variables denote universes initially present in the term
   to type-check and non variable algebraic universes denote the
   universes inferred while type-checking: it is either the successor
   of a universe present in the initial term to type-check or the
   maximum of two algebraic universes
*)

module Universe =
struct
  (* Invariants: non empty, sorted and without duplicates *)

  module Expr = 
  struct
    type t = Level.t * int
    type _t = t
	
    (* Hashing of expressions *)
    module ExprHash = 
    struct
      type t = _t
      type u = Level.t -> Level.t
      let hashcons hdir (b,n as x) = 
	let b' = hdir b in 
	  if b' == b then x else (b',n)
      let eq l1 l2 =
        l1 == l2 || 
        match l1,l2 with
	| (b,n), (b',n') -> b == b' && n == n'

      let hash (x, n) = n + Level.hash x

    end

    module HExpr = 
    struct 

      module H = Hashcons.Make(ExprHash)

      type t = ExprHash.t

      let hcons =
	Hashcons.simple_hcons H.generate H.hcons Level.hcons
      let hash = ExprHash.hash
      let eq x y = x == y ||
	(let (u,n) = x and (v,n') = y in
	   Int.equal n n' && Level.equal u v)

    end

    let hcons = HExpr.hcons

    let make l = hcons (l, 0)

    let compare u v =
      if u == v then 0
      else 
	let (x, n) = u and (x', n') = v in
	  if Int.equal n n' then Level.compare x x'
	  else n - n'

    let prop = make Level.prop
    let set = make Level.set
    let type1 = hcons (Level.set, 1)

    let is_small = function
      | (l,0) -> Level.is_small l
      | _ -> false

    let equal x y = x == y ||
      (let (u,n) = x and (v,n') = y in
	 Int.equal n n' && Level.equal u v)

    let leq (u,n) (v,n') =
      let cmp = Level.compare u v in
	if Int.equal cmp 0 then n <= n'
	else if n <= n' then 
	  (Level.is_prop u && Level.is_small v)
	else false

    let successor (u,n) =
      if Level.is_prop u then type1
      else hcons (u, n + 1)

    let addn k (u,n as x) = 
      if k = 0 then x 
      else if Level.is_prop u then
	hcons (Level.set,n+k)
      else hcons (u,n+k)

    type super_result =
	SuperSame of bool
        (* The level expressions are in cumulativity relation. boolean
           indicates if left is smaller than right?  *)
      | SuperDiff of int
        (* The level expressions are unrelated, the comparison result
           is canonical *)

    (** [super u v] compares two level expressions,
       returning [SuperSame] if they refer to the same level at potentially different
       increments or [SuperDiff] if they are different. The booleans indicate if the
       left expression is "smaller" than the right one in both cases. *)
    let super (u,n as x) (v,n' as y) =
      let cmp = Level.compare u v in
	if Int.equal cmp 0 then SuperSame (n < n')
	else
	  match x, y with
	  | (l,0), (l',0) ->
	     let open RawLevel in
	     (match Level.data l, Level.data l' with
	      | Prop, Prop -> SuperSame false
	      | Prop, _ -> SuperSame true
	      | _, Prop -> SuperSame false
	      | _, _ -> SuperDiff cmp)
	  | _, _ -> SuperDiff cmp

    let to_string (v, n) =
      if Int.equal n 0 then Level.to_string v
      else Level.to_string v ^ "+" ^ string_of_int n

    let pr x = str(to_string x)

    let pr_with f (v, n) = 
      if Int.equal n 0 then f v
      else f v ++ str"+" ++ int n

    let is_level = function
      | (v, 0) -> true
      | _ -> false

    let level = function
      | (v,0) -> Some v
      | _ -> None
	
    let get_level (v,n) = v

    let map f (v, n as x) = 
      let v' = f v in 
	if v' == v then x
	else if Level.is_prop v' && n != 0 then
	  hcons (Level.set, n)
	else hcons (v', n)

  end
    
  let compare_expr = Expr.compare

  module Huniv = HList.Make(Expr.HExpr)
  type t = Huniv.t
  open Huniv
    
  let equal x y = x == y || 
    (Huniv.hash x == Huniv.hash y && 
       Huniv.for_all2 Expr.equal x y)

  let hash = Huniv.hash

  let compare x y =
    if x == y then 0
    else 
      let hx = Huniv.hash x and hy = Huniv.hash y in
      let c = Int.compare hx hy in 
	if c == 0 then
	  Huniv.compare (fun e1 e2 -> compare_expr e1 e2) x y
	else c

  let rec hcons = function
  | Nil -> Huniv.nil
  | Cons (x, _, l) -> Huniv.cons x (hcons l)

  let make l = Huniv.tip (Expr.make l)
  let tip x = Huniv.tip x

  let pr l = match l with
    | Cons (u, _, Nil) -> Expr.pr u
    | _ -> 
      str "max(" ++ hov 0
	(prlist_with_sep pr_comma Expr.pr (to_list l)) ++
        str ")"

  let pr_with f l = match l with
    | Cons (u, _, Nil) -> Expr.pr_with f u
    | _ -> 
      str "max(" ++ hov 0
	(prlist_with_sep pr_comma (Expr.pr_with f) (to_list l)) ++
        str ")"

  let is_level l = match l with
    | Cons (l, _, Nil) -> Expr.is_level l
    | _ -> false

  let rec is_levels l = match l with
    | Cons (l, _, r) -> Expr.is_level l && is_levels r
    | Nil -> true

  let level l = match l with
    | Cons (l, _, Nil) -> Expr.level l
    | _ -> None

  let levels l = 
    fold (fun x acc -> LSet.add (Expr.get_level x) acc) l LSet.empty

  let is_small u = 
    match u with
    | Cons (l, _, Nil) -> Expr.is_small l
    | _ -> false

  (* The lower predicative level of the hierarchy that contains (impredicative)
     Prop and singleton inductive types *)
  let type0m = tip Expr.prop

  (* The level of sets *)
  let type0 = tip Expr.set

  (* When typing [Prop] and [Set], there is no constraint on the level,
     hence the definition of [type1_univ], the type of [Prop] *)    
  let type1 = tip (Expr.successor Expr.set)

  let is_type0m x = equal type0m x
  let is_type0 x = equal type0 x

  (* Returns the formal universe that lies just above the universe variable u.
     Used to type the sort u. *)
  let super l = 
    if is_small l then type1
    else
      Huniv.map (fun x -> Expr.successor x) l

  let addn n l =
    Huniv.map (fun x -> Expr.addn n x) l

  let rec merge_univs l1 l2 =
    match l1, l2 with
    | Nil, _ -> l2
    | _, Nil -> l1
    | Cons (h1, _, t1), Cons (h2, _, t2) ->
       let open Expr in
       (match super h1 h2 with
	| SuperSame true (* h1 < h2 *) -> merge_univs t1 l2
	| SuperSame false -> merge_univs l1 t2
	| SuperDiff c ->
           if c <= 0 (* h1 < h2 is name order *)
	   then cons h1 (merge_univs t1 l2)
	   else cons h2 (merge_univs l1 t2))

  let sort u =
    let rec aux a l = 
      match l with
      | Cons (b, _, l') ->
	let open Expr in
        (match super a b with
	 | SuperSame false -> aux a l'
	 | SuperSame true -> l
	 | SuperDiff c ->
	    if c <= 0 then cons a l
	    else cons b (aux a l'))
      | Nil -> cons a l
    in 
      fold (fun a acc -> aux a acc) u nil
	
  (* Returns the formal universe that is greater than the universes u and v.
     Used to type the products. *)
  let sup x y = merge_univs x y

  let empty = nil

  let exists = Huniv.exists

  let for_all = Huniv.for_all

  let smartmap = Huniv.smartmap

end

type universe = Universe.t

(* The level of predicative Set *)
let type0m_univ = Universe.type0m
let type0_univ = Universe.type0
let type1_univ = Universe.type1
let is_type0m_univ = Universe.is_type0m
let is_type0_univ = Universe.is_type0
let is_univ_variable l = Universe.level l != None
let is_small_univ = Universe.is_small
let pr_uni = Universe.pr

let sup = Universe.sup
let super = Universe.super

open Universe

let universe_level = Universe.level


type constraint_type = Lt | Le | Eq

type explanation = (constraint_type * universe) list

let constraint_type_ord c1 c2 = match c1, c2 with
| Lt, Lt -> 0
| Lt, _ -> -1
| Le, Lt -> 1
| Le, Le -> 0
| Le, Eq -> -1
| Eq, Eq -> 0
| Eq, _ -> 1

(* Universe inconsistency: error raised when trying to enforce a relation
   that would create a cycle in the graph of universes. *)

type univ_inconsistency = constraint_type * universe * universe * explanation option

exception UniverseInconsistency of univ_inconsistency

let error_inconsistency o u v (p:explanation option) =
  raise (UniverseInconsistency (o,make u,make v,p))

(* Constraints and sets of constraints. *)    

type univ_constraint = Level.t * constraint_type * Level.t

let pr_constraint_type op = 
  let op_str = match op with
    | Lt -> " < "
    | Le -> " <= "
    | Eq -> " = "
  in str op_str

module UConstraintOrd =
struct
  type t = univ_constraint
  let compare (u,c,v) (u',c',v') =
    let i = constraint_type_ord c c' in
    if not (Int.equal i 0) then i
    else
      let i' = Level.compare u u' in
      if not (Int.equal i' 0) then i'
      else Level.compare v v'
end

module Constraint = 
struct 
  module S = Set.Make(UConstraintOrd)
  include S

  let pr prl c =
    fold (fun (u1,op,u2) pp_std ->
      pp_std ++ prl u1 ++ pr_constraint_type op ++
	prl u2 ++ fnl () )  c (str "")

end

let empty_constraint = Constraint.empty
let union_constraint = Constraint.union
let eq_constraint = Constraint.equal

type constraints = Constraint.t

module Hconstraint =
  Hashcons.Make(
    struct
      type t = univ_constraint
      type u = universe_level -> universe_level
      let hashcons hul (l1,k,l2) = (hul l1, k, hul l2)
      let eq (l1,k,l2) (l1',k',l2') =
	l1 == l1' && k == k' && l2 == l2'
      let hash = Hashtbl.hash
    end)

module Hconstraints =
  Hashcons.Make(
    struct
      type t = constraints
      type u = univ_constraint -> univ_constraint
      let hashcons huc s =
	Constraint.fold (fun x -> Constraint.add (huc x)) s Constraint.empty
      let eq s s' =
	List.for_all2eq (==)
	  (Constraint.elements s)
	  (Constraint.elements s')
      let hash = Hashtbl.hash
    end)

let hcons_constraint = Hashcons.simple_hcons Hconstraint.generate Hconstraint.hcons Level.hcons
let hcons_constraints = Hashcons.simple_hcons Hconstraints.generate Hconstraints.hcons hcons_constraint


(** A value with universe constraints. *)
type 'a constrained = 'a * constraints

let constraints_of (_, cst) = cst

(** Constraint functions. *)

type 'a constraint_function = 'a -> 'a -> constraints -> constraints

let enforce_eq_level u v c =
  (* We discard trivial constraints like u=u *)
  if Level.equal u v then c 
  else if Level.apart u v then
    error_inconsistency Eq u v None
  else Constraint.add (u,Eq,v) c

let enforce_eq u v c =
  match Universe.level u, Universe.level v with
    | Some u, Some v -> enforce_eq_level u v c
    | _ -> anomaly (Pp.str "A universe comparison can only happen between variables.")

let check_univ_eq u v = Universe.equal u v

let enforce_eq u v c =
  if check_univ_eq u v then c
  else enforce_eq u v c

let constraint_add_leq v u c =
  (* We just discard trivial constraints like u<=u *)
  if Expr.equal v u then c
  else 
    match v, u with
    | (x,n), (y,m) -> 
    let j = m - n in
      if j = -1 (* n = m+1, v+1 <= u <-> v < u *) then
	Constraint.add (x,Lt,y) c
      else if j <= -1 (* n = m+k, v+k <= u <-> v+(k-1) < u *) then
	if Level.equal x y then (* u+(k+1) <= u *)
	  raise (UniverseInconsistency (Le, Universe.tip v, Universe.tip u, None))
	else anomaly (Pp.str"Unable to handle arbitrary u+k <= v constraints.")
      else if j = 0 then
	Constraint.add (x,Le,y) c
      else (* j >= 1 *) (* m = n + k, u <= v+k *)
	if Level.equal x y then c (* u <= u+k, trivial *)
	else if Level.is_small x then c (* Prop,Set <= u+S k, trivial *)
	else anomaly (Pp.str"Unable to handle arbitrary u <= v+k constraints.")
	  
let check_univ_leq_one u v = Universe.exists (Expr.leq u) v

let check_univ_leq u v = 
  Universe.for_all (fun u -> check_univ_leq_one u v) u

let enforce_leq u v c =
  let open Universe.Huniv in
  let rec aux acc v =
  match v with
  | Cons (v, _, l) ->
    aux (fold (fun u -> constraint_add_leq u v) u c) l
  | Nil -> acc
  in aux c v

let enforce_leq u v c =
  if check_univ_leq u v then c
  else enforce_leq u v c

let enforce_leq_level u v c =
  if Level.equal u v then c else Constraint.add (u,Le,v) c

let enforce_univ_constraint (u,d,v) =
  match d with
  | Eq -> enforce_eq u v
  | Le -> enforce_leq u v
  | Lt -> enforce_leq (super u) v

(* Miscellaneous functions to remove or test local univ assumed to
   occur in a universe *)

let univ_level_mem u v = Huniv.mem (Expr.make u) v

let univ_level_rem u v min = 
  match Universe.level v with
  | Some u' -> if Level.equal u u' then min else v
  | None -> Huniv.remove (Universe.Expr.make u) v

(* Is u mentionned in v (or equals to v) ? *)


(**********************************************************************)
(** Universe polymorphism                                             *)
(**********************************************************************)

(** A universe level substitution, note that no algebraic universes are
    involved *)

type universe_level_subst = universe_level universe_map

(** A full substitution might involve algebraic universes *)
type universe_subst = universe universe_map

let level_subst_of f = 
  fun l -> 
    try let u = f l in 
	  match Universe.level u with
	  | None -> l
	  | Some l -> l
    with Not_found -> l
     
module Instance : sig 
    type t = Level.t array

    val empty : t
    val is_empty : t -> bool
      
    val of_array : Level.t array -> t
    val to_array : t -> Level.t array

    val append : t -> t -> t
    val equal : t -> t -> bool
    val length : t -> int

    val hcons : t -> t
    val hash : t -> int

    val share : t -> t * int

    val subst_fn : universe_level_subst_fn -> t -> t
    
    val pr : (Level.t -> Pp.std_ppcmds) -> t -> Pp.std_ppcmds
    val levels : t -> LSet.t
end = 
struct
  type t = Level.t array

  let empty : t = [||]

  module HInstancestruct =
  struct
    type _t = t
    type t = _t
    type u = Level.t -> Level.t

    let hashcons huniv a = 
      let len = Array.length a in
	if Int.equal len 0 then empty
	else begin
	  for i = 0 to len - 1 do
	    let x = Array.unsafe_get a i in
	    let x' = huniv x in
	      if x == x' then ()
	      else Array.unsafe_set a i x'
	  done;
	  a
	end

    let eq t1 t2 =
      t1 == t2 ||
	(Int.equal (Array.length t1) (Array.length t2) &&
	   let rec aux i =
	     (Int.equal i (Array.length t1)) || (t1.(i) == t2.(i) && aux (i + 1))
	   in aux 0)
	
    let hash a = 
      let accu = ref 0 in
	for i = 0 to Array.length a - 1 do
	  let l = Array.unsafe_get a i in
	  let h = Level.hash l in
	    accu := Hashset.Combine.combine !accu h;
	done;
	(* [h] must be positive. *)
	let h = !accu land 0x3FFFFFFF in
	  h
  end

  module HInstance = Hashcons.Make(HInstancestruct)

  let hcons = Hashcons.simple_hcons HInstance.generate HInstance.hcons Level.hcons
    
  let hash = HInstancestruct.hash
    
  let share a = (hcons a, hash a)
	      
  let empty = hcons [||]

  let is_empty x = Int.equal (Array.length x) 0

  let append x y =
    if Array.length x = 0 then y
    else if Array.length y = 0 then x 
    else Array.append x y

  let of_array a =
    assert(Array.for_all (fun x -> not (Level.is_prop x)) a);
    a

  let to_array a = a

  let length a = Array.length a

  let subst_fn fn t = 
    let t' = CArray.smartmap fn t in
      if t' == t then t else of_array t'

  let levels x = LSet.of_array x

  let pr =
    prvect_with_sep spc

  let equal t u = 
    t == u ||
      (Array.is_empty t && Array.is_empty u) ||
      (CArray.for_all2 Level.equal t u 
	 (* Necessary as universe instances might come from different modules and 
	    unmarshalling doesn't preserve sharing *))

end

let enforce_eq_instances x y = 
  let ax = Instance.to_array x and ay = Instance.to_array y in
    if Array.length ax != Array.length ay then
      anomaly (Pp.(++) (Pp.str "Invalid argument: enforce_eq_instances called with")
		 (Pp.str " instances of different lengths."));
    CArray.fold_right2 enforce_eq_level ax ay

type universe_instance = Instance.t

type 'a puniverses = 'a * Instance.t
let out_punivs (x, y) = x
let in_punivs x = (x, Instance.empty)
let eq_puniverses f (x, u) (y, u') =
  f x y && Instance.equal u u'

(** A context of universe levels with universe constraints,
    representing local universe variables and constraints *)

module UContext =
struct
  type t = Instance.t constrained

  let make x = x

  (** Universe contexts (variables as a list) *)
  let empty = (Instance.empty, Constraint.empty)
  let is_empty (univs, cst) = Instance.is_empty univs && Constraint.is_empty cst

  let pr prl (univs, cst as ctx) =
    if is_empty ctx then mt() else
      h 0 (Instance.pr prl univs ++ str " |= ") ++ h 0 (v 0 (Constraint.pr prl cst))

  let hcons (univs, cst) =
    (Instance.hcons univs, hcons_constraints cst)

  let instance (univs, cst) = univs
  let constraints (univs, cst) = cst

  let union (univs, cst) (univs', cst') =
    Instance.append univs univs', Constraint.union cst cst'

  let dest x = x

  let size (x,_) = Instance.length x

end

type universe_context = UContext.t
let hcons_universe_context = UContext.hcons

(** Universe info for inductive types: A context of universe levels
    with universe constraints, representing local universe variables
    and constraints, together with a context of universe levels with
    universe constraints, representing conditions for subtyping used
    for inductive types.

    This data structure maintains the invariant that the context for
    subtyping constraints is exactly twice as big as the context for
    universe constraints. *)
module UInfoInd =
struct
  type t = universe_context * universe_context

  let make x =
    if (Instance.length (UContext.instance (snd x))) =
       (Instance.length (UContext.instance (fst x))) * 2 then x
    else anomaly (Pp.str "Invalid subtyping information encountered!")

  let empty = (UContext.empty, UContext.empty)
  let is_empty (univcst, subtypcst) = UContext.is_empty univcst && UContext.is_empty subtypcst

  let halve_context ctx =
    let len = Array.length (Instance.to_array ctx) in
    let halflen = len / 2 in
    (Instance.of_array (Array.sub (Instance.to_array ctx) 0 halflen),
     Instance.of_array (Array.sub (Instance.to_array ctx) halflen halflen))

  let pr prl (univcst, subtypcst) =
    if UContext.is_empty univcst then mt() else
      let (ctx, ctx') = halve_context (UContext.instance subtypcst) in
      (UContext.pr prl univcst) ++ fnl () ++ fnl () ++
        h 0 (str "~@{" ++ Instance.pr prl ctx ++ str "} <= ~@{" ++ Instance.pr prl ctx' ++ str "} iff ")
         ++ fnl () ++ h 0 (v 0 (Constraint.pr prl (UContext.constraints subtypcst)))

  let hcons (univcst, subtypcst) =
    (UContext.hcons univcst, UContext.hcons subtypcst)

  let univ_context (univcst, subtypcst) = univcst
  let subtyp_context (univcst, subtypcst) = subtypcst

  let create_trivial_subtyping ctx ctx' =
    CArray.fold_left_i
      (fun i cst l -> Constraint.add (l, Eq, Array.get ctx' i) cst)
      Constraint.empty (Instance.to_array ctx)

  (** This function takes a universe context representing constraints
      of an inductive and a Instance.t of fresh universe names for the
      subtyping (with the same length as the context in the given
      universe context) and produces a UInfoInd.t that with the
      trivial subtyping relation. *)
  let from_universe_context univcst freshunivs =
    let inst = (UContext.instance univcst) in
    assert (Instance.length freshunivs = Instance.length inst);
    (univcst, UContext.make (Instance.append inst freshunivs,
                             create_trivial_subtyping inst freshunivs))

  let subtyping_susbst (univcst, subtypcst) = 
      let (ctx, ctx') = (halve_context (UContext.instance subtypcst))in
      Array.fold_left2 (fun subst l1 l2 -> LMap.add l1 l2 subst) LMap.empty ctx ctx'

  let dest x = x

  let size ((x,_), _) = Instance.length x

end

type universe_info_ind = UInfoInd.t
let hcons_universe_info_ind = UInfoInd.hcons

(** A set of universes with universe constraints.
    We linearize the set to a list after typechecking. 
    Beware, representation could change.
*)

module ContextSet =
struct
  type t = universe_set constrained

  let empty = (LSet.empty, Constraint.empty)
  let is_empty (univs, cst) = LSet.is_empty univs && Constraint.is_empty cst

  let equal (univs, cst as x) (univs', cst' as y) =
    x == y || (LSet.equal univs univs' && Constraint.equal cst cst')
									
  let of_set s = (s, Constraint.empty)
  let singleton l = of_set (LSet.singleton l)
  let of_instance i = of_set (Instance.levels i)

  let union (univs, cst as x) (univs', cst' as y) =
    if x == y then x
    else LSet.union univs univs', Constraint.union cst cst'

  let append (univs, cst) (univs', cst') =
    let univs = LSet.fold LSet.add univs univs' in
    let cst = Constraint.fold Constraint.add cst cst' in
    (univs, cst)

  let diff (univs, cst) (univs', cst') =
    LSet.diff univs univs', Constraint.diff cst cst'

  let add_universe u (univs, cst) =
    LSet.add u univs, cst

  let add_constraints cst' (univs, cst) =
    univs, Constraint.union cst cst'

  let add_instance inst (univs, cst) =
    let v = Instance.to_array inst in
    let fold accu u = LSet.add u accu in
    let univs = Array.fold_left fold univs v in
    (univs, cst)

  let sort_levels a = 
    Array.sort Level.natural_compare a; a

  let to_context (ctx, cst) =
    (Instance.of_array (sort_levels (Array.of_list (LSet.elements ctx))), cst)

  let of_context (ctx, cst) =
    (Instance.levels ctx, cst)

  let pr prl (univs, cst as ctx) =
    if is_empty ctx then mt() else
      h 0 (LSet.pr prl univs ++ str " |= ") ++ h 0 (v 0 (Constraint.pr prl cst))

  let constraints (univs, cst) = cst
  let levels (univs, cst) = univs

end

type universe_context_set = ContextSet.t

(** A value in a universe context (resp. context set). *)
type 'a in_universe_context = 'a * universe_context
type 'a in_universe_context_set = 'a * universe_context_set

(** Substitutions. *)

let empty_subst = LMap.empty
let is_empty_subst = LMap.is_empty

let empty_level_subst = LMap.empty
let is_empty_level_subst = LMap.is_empty

(** Substitution functions *)

(** With level to level substitutions. *)
let subst_univs_level_level subst l =
  try LMap.find l subst
  with Not_found -> l

let subst_univs_level_universe subst u =
  let f x = Universe.Expr.map (fun u -> subst_univs_level_level subst u) x in
  let u' = Universe.smartmap f u in
    if u == u' then u
    else Universe.sort u'

let subst_univs_level_instance subst i =
  let i' = Instance.subst_fn (subst_univs_level_level subst) i in
    if i == i' then i
    else i'
	
let subst_univs_level_constraint subst (u,d,v) =
  let u' = subst_univs_level_level subst u 
  and v' = subst_univs_level_level subst v in
    if d != Lt && Level.equal u' v' then None
    else Some (u',d,v')

let subst_univs_level_constraints subst csts =
  Constraint.fold 
    (fun c -> Option.fold_right Constraint.add (subst_univs_level_constraint subst c))
    csts Constraint.empty 

(** With level to universe substitutions. *)
type universe_subst_fn = universe_level -> universe

let make_subst subst = fun l -> LMap.find l subst

let subst_univs_expr_opt fn (l,n) =
  Universe.addn n (fn l)

let subst_univs_universe fn ul =
  let subst, nosubst = 
    Universe.Huniv.fold (fun u (subst,nosubst) -> 
      try let a' = subst_univs_expr_opt fn u in
	    (a' :: subst, nosubst)
      with Not_found -> (subst, u :: nosubst))
      ul ([], [])
  in 
    if CList.is_empty subst then ul
    else 
      let substs = 
	List.fold_left Universe.merge_univs Universe.empty subst
      in
	List.fold_left (fun acc u -> Universe.merge_univs acc (Universe.Huniv.tip u))
	  substs nosubst

let subst_univs_level fn l = 
  try Some (fn l)
  with Not_found -> None

let subst_univs_constraint fn (u,d,v as c) cstrs =
  let u' = subst_univs_level fn u in
  let v' = subst_univs_level fn v in
  match u', v' with
  | None, None -> Constraint.add c cstrs
  | Some u, None -> enforce_univ_constraint (u,d,make v) cstrs
  | None, Some v -> enforce_univ_constraint (make u,d,v) cstrs
  | Some u, Some v -> enforce_univ_constraint (u,d,v) cstrs

let subst_univs_constraints subst csts =
  Constraint.fold 
    (fun c cstrs -> subst_univs_constraint subst c cstrs)
    csts Constraint.empty 

let subst_instance_level s l =
  match l.Level.data with
  | Level.Var n -> s.(n) 
  | _ -> l

let subst_instance_instance s i = 
  Array.smartmap (fun l -> subst_instance_level s l) i

let subst_instance_universe s u =
  let f x = Universe.Expr.map (fun u -> subst_instance_level s u) x in
  let u' = Universe.smartmap f u in
    if u == u' then u
    else Universe.sort u'

let subst_instance_constraint s (u,d,v as c) =
  let u' = subst_instance_level s u in
  let v' = subst_instance_level s v in
    if u' == u && v' == v then c
    else (u',d,v')

let subst_instance_constraints s csts =
  Constraint.fold 
    (fun c csts -> Constraint.add (subst_instance_constraint s c) csts)
    csts Constraint.empty 

(** Substitute instance inst for ctx in csts *)
let instantiate_univ_context (ctx, csts) = 
  (ctx, subst_instance_constraints ctx csts)

(** Substitute instance inst for ctx in universe constraints and subtyping constraints *)
let instantiate_univ_info_ind (univcst, subtpcst) = 
  (instantiate_univ_context univcst, instantiate_univ_context subtpcst)

let instantiate_univ_constraints u (_, csts) = 
  subst_instance_constraints u csts

let make_instance_subst i = 
  let arr = Instance.to_array i in
    Array.fold_left_i (fun i acc l ->
      LMap.add l (Level.var i) acc)
      LMap.empty arr

let make_inverse_instance_subst i = 
  let arr = Instance.to_array i in
    Array.fold_left_i (fun i acc l ->
      LMap.add (Level.var i) l acc)
      LMap.empty arr

let abstract_universes poly ctx =
  let instance = UContext.instance ctx in
    if poly then
      let subst = make_instance_subst instance in
      let cstrs = subst_univs_level_constraints subst 
	(UContext.constraints ctx)
      in
      let ctx = UContext.make (instance, cstrs) in
	subst, ctx
    else empty_level_subst, ctx

(** Pretty-printing *)

let pr_constraints prl = Constraint.pr prl

let pr_universe_context = UContext.pr

let pr_universe_info_ind = UInfoInd.pr

let pr_universe_context_set = ContextSet.pr

let pr_universe_subst = 
  LMap.pr (fun u -> str" := " ++ Universe.pr u ++ spc ())

let pr_universe_level_subst = 
  LMap.pr (fun u -> str" := " ++ Level.pr u ++ spc ())

module Huniverse_set = 
  Hashcons.Make(
    struct
      type t = universe_set
      type u = universe_level -> universe_level
      let hashcons huc s =
	LSet.fold (fun x -> LSet.add (huc x)) s LSet.empty
      let eq s s' =
	LSet.equal s s'
      let hash = Hashtbl.hash
    end)

let hcons_universe_set = 
  Hashcons.simple_hcons Huniverse_set.generate Huniverse_set.hcons Level.hcons

let hcons_universe_context_set (v, c) = 
  (hcons_universe_set v, hcons_constraints c)

let hcons_univ x = Universe.hcons x

let explain_universe_inconsistency prl (o,u,v,p) =
  let pr_uni = Universe.pr_with prl in
  let pr_rel = function
    | Eq -> str"=" | Lt -> str"<" | Le -> str"<=" 
  in
  let reason = match p with
    | None | Some [] -> mt()
    | Some p ->
      str " because" ++ spc() ++ pr_uni v ++
	prlist (fun (r,v) -> spc() ++ pr_rel r ++ str" " ++ pr_uni v)
	p ++
	(if Universe.equal (snd (List.last p)) u then mt() else
	    (spc() ++ str "= " ++ pr_uni u)) 
  in
    str "Cannot enforce" ++ spc() ++ pr_uni u ++ spc() ++
      pr_rel o ++ spc() ++ pr_uni v ++ reason

let compare_levels = Level.compare
let eq_levels = Level.equal
let equal_universes = Universe.equal


let subst_instance_constraints = 
  if Flags.profile then 
    let key = Profile.declare_profile "subst_instance_constraints" in
      Profile.profile2 key subst_instance_constraints
  else subst_instance_constraints