(*  Title:      Pure/sorts.ML

    ID:         $Id$

    Author:     Markus Wenzel and Stefan Berghofer, TU Muenchen

The order-sorted algebra of type classes.

Classes denote (possibly empty) collections of types that are

partially ordered by class inclusion. They are represented

symbolically by strings.

Sorts are intersections of finitely many classes. They are represented

by lists of classes.  Normal forms of sorts are sorted lists of

minimal classes (wrt. current class inclusion).

*)

signature SORTS =

sig

  val union: sort list -> sort list -> sort list

  val subtract: sort list -> sort list -> sort list

  val remove_sort: sort -> sort list -> sort list

  val insert_sort: sort -> sort list -> sort list

  val insert_typ: typ -> sort list -> sort list

  val insert_typs: typ list -> sort list -> sort list

  val insert_term: term -> sort list -> sort list

  val insert_terms: term list -> sort list -> sort list

  type algebra

  val rep_algebra: algebra ->

   {classes: serial Graph.T,

    arities: (class * (class * sort list)) list Symtab.table}

  val all_classes: algebra -> class list

  val minimal_classes: algebra -> class list

  val super_classes: algebra -> class -> class list

  val class_less: algebra -> class * class -> bool

  val class_le: algebra -> class * class -> bool

  val sort_eq: algebra -> sort * sort -> bool

  val sort_le: algebra -> sort * sort -> bool

  val sorts_le: algebra -> sort list * sort list -> bool

  val inter_sort: algebra -> sort * sort -> sort

  val certify_class: algebra -> class -> class    (*exception TYPE*)

  val certify_sort: algebra -> sort -> sort       (*exception TYPE*)

  val add_class: Pretty.pp -> class * class list -> algebra -> algebra

  val add_classrel: Pretty.pp -> class * class -> algebra -> algebra

  val add_arities: Pretty.pp -> string * (class * sort list) list -> algebra -> algebra

  val empty_algebra: algebra

  val merge_algebra: Pretty.pp -> algebra * algebra -> algebra

  val subalgebra: Pretty.pp -> (class -> bool) -> (class * string -> sort list)

    -> algebra -> (sort -> sort) * algebra

  type class_error

  val msg_class_error: Pretty.pp -> class_error -> string

  val class_error: Pretty.pp -> class_error -> 'a

  exception CLASS_ERROR of class_error

  val mg_domain: algebra -> string -> sort -> sort list   (*exception CLASS_ERROR*)

  val of_sort: algebra -> typ * sort -> bool

  val of_sort_derivation: Pretty.pp -> algebra ->

    {class_relation: 'a * class -> class -> 'a,

     type_constructor: string -> ('a * class) list list -> class -> 'a,

     type_variable: typ -> ('a * class) list} ->

    typ * sort -> 'a list   (*exception CLASS_ERROR*)

  val witness_sorts: algebra -> string list -> sort list -> sort list -> (typ * sort) list

end;

structure Sorts: SORTS =

struct

(** ordered lists of sorts **)

val op union = OrdList.union Term.sort_ord;

val subtract = OrdList.subtract Term.sort_ord;

val remove_sort = OrdList.remove Term.sort_ord;

val insert_sort = OrdList.insert Term.sort_ord;

fun insert_typ (TFree (_, S)) Ss = insert_sort S Ss

  | insert_typ (TVar (_, S)) Ss = insert_sort S Ss

  | insert_typ (Type (_, Ts)) Ss = insert_typs Ts Ss

and insert_typs [] Ss = Ss

  | insert_typs (T :: Ts) Ss = insert_typs Ts (insert_typ T Ss);

fun insert_term (Const (_, T)) Ss = insert_typ T Ss

  | insert_term (Free (_, T)) Ss = insert_typ T Ss

  | insert_term (Var (_, T)) Ss = insert_typ T Ss

  | insert_term (Bound _) Ss = Ss

  | insert_term (Abs (_, T, t)) Ss = insert_term t (insert_typ T Ss)

  | insert_term (t $ u) Ss = insert_term t (insert_term u Ss);

fun insert_terms [] Ss = Ss

  | insert_terms (t :: ts) Ss = insert_terms ts (insert_term t Ss);

(** order-sorted algebra **)

(*

  classes: graph representing class declarations together with proper

    subclass relation, which needs to be transitive and acyclic.

  arities: table of association lists of all type arities; (t, ars)

    means that type constructor t has the arities ars; an element

    (c, (c0, Ss)) of ars represents the arity t::(Ss)c being derived

    via c0 <= c.  "Coregularity" of the arities structure requires

    that for any two declarations t::(Ss1)c1 and t::(Ss2)c2 such that

    c1 <= c2 holds Ss1 <= Ss2.

*)

datatype algebra = Algebra of

 {classes: serial Graph.T,

  arities: (class * (class * sort list)) list Symtab.table};

fun rep_algebra (Algebra args) = args;

val classes_of = #classes o rep_algebra;

val arities_of = #arities o rep_algebra;

fun make_algebra (classes, arities) =

  Algebra {classes = classes, arities = arities};

fun map_classes f (Algebra {classes, arities}) = make_algebra (f classes, arities);

fun map_arities f (Algebra {classes, arities}) = make_algebra (classes, f arities);

(* classes *)

fun all_classes (Algebra {classes, ...}) = Graph.all_preds classes (Graph.maximals classes);

val minimal_classes = Graph.minimals o classes_of;

val super_classes = Graph.imm_succs o classes_of;

(* class relations *)

val class_less = Graph.is_edge o classes_of;

fun class_le algebra (c1, c2) = c1 = c2 orelse class_less algebra (c1, c2);

(* sort relations *)

fun sort_le algebra (S1, S2) =

  forall (fn c2 => exists (fn c1 => class_le algebra (c1, c2)) S1) S2;

fun sorts_le algebra (Ss1, Ss2) =

  ListPair.all (sort_le algebra) (Ss1, Ss2);

fun sort_eq algebra (S1, S2) =

  sort_le algebra (S1, S2) andalso sort_le algebra (S2, S1);

(* intersection *)

fun inter_class algebra c S =

  let

    fun intr [] = [c]

      | intr (S' as c' :: c's) =

          if class_le algebra (c', c) then S'

          else if class_le algebra (c, c') then intr c's

          else c' :: intr c's

  in intr S end;

fun inter_sort algebra (S1, S2) =

  sort_strings (fold (inter_class algebra) S1 S2);

(* normal form *)

fun norm_sort _ [] = []

  | norm_sort _ (S as [_]) = S

  | norm_sort algebra S =

      filter (fn c => not (exists (fn c' => class_less algebra (c', c)) S)) S

      |> sort_distinct string_ord;

(* certify *)

fun certify_class algebra c =

  if can (Graph.get_node (classes_of algebra)) c then c

  else raise TYPE ("Undeclared class: " ^ quote c, [], []);

fun certify_sort classes = norm_sort classes o map (certify_class classes);

(** build algebras **)

(* classes *)

fun err_dup_classes cs =

  error ("Duplicate declaration of class(es): " ^ commas_quote cs);

fun err_cyclic_classes pp css =

  error (cat_lines (map (fn cs =>

    "Cycle in class relation: " ^ Pretty.string_of_classrel pp cs) css));

fun add_class pp (c, cs) = map_classes (fn classes =>

  let

    val classes' = classes |> Graph.new_node (c, serial ())

      handle Graph.DUP dup => err_dup_classes [dup];

    val classes'' = classes' |> fold Graph.add_edge_trans_acyclic (map (pair c) cs)

      handle Graph.CYCLES css => err_cyclic_classes pp css;

  in classes'' end);

(* arities *)

local

fun for_classes _ NONE = ""

  | for_classes pp (SOME (c1, c2)) =

      " for classes " ^ Pretty.string_of_classrel pp [c1, c2];

fun err_conflict pp t cc (c, Ss) (c', Ss') =

  error ("Conflict of type arities" ^ for_classes pp cc ^ ":\n  " ^

    Pretty.string_of_arity pp (t, Ss, [c]) ^ " and\n  " ^

    Pretty.string_of_arity pp (t, Ss', [c']));

fun coregular pp algebra t (c, (c0, Ss)) ars =

  let

    fun conflict (c', (_, Ss')) =

      if class_le algebra (c, c') andalso not (sorts_le algebra (Ss, Ss')) then

        SOME ((c, c'), (c', Ss'))

      else if class_le algebra (c', c) andalso not (sorts_le algebra (Ss', Ss)) then

        SOME ((c', c), (c', Ss'))

      else NONE;

  in

    (case get_first conflict ars of

      SOME ((c1, c2), (c', Ss')) => err_conflict pp t (SOME (c1, c2)) (c, Ss) (c', Ss')

    | NONE => (c, (c0, Ss)) :: ars)

  end;

fun complete algebra (c0, Ss) = map (rpair (c0, Ss)) (c0 :: super_classes algebra c0);

fun insert pp algebra t (c, (c0, Ss)) ars =

  (case AList.lookup (op =) ars c of

    NONE => coregular pp algebra t (c, (c0, Ss)) ars

  | SOME (_, Ss') =>

      if sorts_le algebra (Ss, Ss') then ars

      else if sorts_le algebra (Ss', Ss) then

        coregular pp algebra t (c, (c0, Ss))

          (filter_out (fn (c'', (_, Ss'')) => c = c'' andalso Ss'' = Ss') ars)

      else err_conflict pp t NONE (c, Ss) (c, Ss'));

fun insert_ars pp algebra (t, ars) arities =

  let val ars' =

    Symtab.lookup_list arities t

    |> fold_rev (fold_rev (insert pp algebra t)) (map (complete algebra) ars)

  in Symtab.update (t, ars') arities end;

in

fun add_arities pp arg algebra = algebra |> map_arities (insert_ars pp algebra arg);

fun add_arities_table pp algebra =

  Symtab.fold (fn (t, ars) => insert_ars pp algebra (t, map snd ars));

end;

(* classrel *)

fun rebuild_arities pp algebra = algebra |> map_arities (fn arities =>

  Symtab.empty

  |> add_arities_table pp algebra arities);

fun add_classrel pp rel = rebuild_arities pp o map_classes (fn classes =>

  classes |> Graph.add_edge_trans_acyclic rel

    handle Graph.CYCLES css => err_cyclic_classes pp css);

(* empty and merge *)

val empty_algebra = make_algebra (Graph.empty, Symtab.empty);

fun merge_algebra pp

   (Algebra {classes = classes1, arities = arities1},

    Algebra {classes = classes2, arities = arities2}) =

  let

    val classes' = Graph.merge_trans_acyclic (op =) (classes1, classes2)

      handle Graph.DUPS cs => err_dup_classes cs

          | Graph.CYCLES css => err_cyclic_classes pp css;

    val algebra0 = make_algebra (classes', Symtab.empty);

    val arities' = Symtab.empty

      |> add_arities_table pp algebra0 arities1

      |> add_arities_table pp algebra0 arities2;

  in make_algebra (classes', arities') end;

(* subalgebra *)

fun subalgebra pp P sargs (algebra as Algebra {classes, arities}) =

  let

    val restrict_sort = norm_sort algebra o filter P o Graph.all_succs classes;

    fun restrict_arity tyco (c, (_, Ss)) =

      if P c then

        SOME (c, (c, Ss |> map2 (curry (inter_sort algebra)) (sargs (c, tyco))

          |> map restrict_sort))

      else NONE;

    val classes' = classes |> Graph.subgraph P;

    val arities' = arities |> Symtab.map' (map_filter o restrict_arity);

  in (restrict_sort, rebuild_arities pp (make_algebra (classes', arities'))) end;

(** sorts of types **)

(* errors *)

datatype class_error = NoClassrel of class * class | NoArity of string * class;

fun msg_class_error pp (NoClassrel (c1, c2)) =

      "No class relation " ^ Pretty.string_of_classrel pp [c1, c2]

  | msg_class_error pp (NoArity (a, c)) =

      "No type arity " ^ Pretty.string_of_arity pp (a, [], [c]);

fun class_error pp = error o msg_class_error pp;

exception CLASS_ERROR of class_error;

(* mg_domain *)

fun mg_domain algebra a S =

  let

    val arities = arities_of algebra;

    fun dom c =

      (case AList.lookup (op =) (Symtab.lookup_list arities a) c of

        NONE => raise CLASS_ERROR (NoArity (a, c))

      | SOME (_, Ss) => Ss);

    fun dom_inter c Ss = ListPair.map (inter_sort algebra) (dom c, Ss);

  in

    (case S of

      [] => raise Fail "Unknown domain of empty intersection"

    | c :: cs => fold dom_inter cs (dom c))

  end;

(* of_sort *)

fun of_sort algebra =

  let

    fun ofS (_, []) = true

      | ofS (TFree (_, S), S') = sort_le algebra (S, S')

      | ofS (TVar (_, S), S') = sort_le algebra (S, S')

      | ofS (Type (a, Ts), S) =

          let val Ss = mg_domain algebra a S in

            ListPair.all ofS (Ts, Ss)

          end handle CLASS_ERROR _ => false;

  in ofS end;

(* of_sort_derivation *)

fun of_sort_derivation pp algebra {class_relation, type_constructor, type_variable} =

  let

    val {classes, arities} = rep_algebra algebra;

    fun weaken_path (x, c1 :: c2 :: cs) =

          weaken_path (class_relation (x, c1) c2, c2 :: cs)

      | weaken_path (x, _) = x;

    fun weaken (x, c1) c2 =

      (case Graph.irreducible_paths classes (c1, c2) of

        [] => raise CLASS_ERROR (NoClassrel (c1, c2))

      | cs :: _ => weaken_path (x, cs));

    fun weakens S1 S2 = S2 |> map (fn c2 =>

      (case S1 |> find_first (fn (_, c1) => class_le algebra (c1, c2)) of

        SOME d1 => weaken d1 c2

      | NONE => error ("Cannot derive subsort relation " ^

          Pretty.string_of_sort pp (map #2 S1) ^ " < " ^ Pretty.string_of_sort pp S2)));

    fun derive _ [] = []

      | derive (Type (a, Ts)) S =

          let

            val Ss = mg_domain algebra a S;

            val dom = map2 (fn T => fn S => derive T S ~~ S) Ts Ss;

          in

            S |> map (fn c =>

              let

                val (c0, Ss') = the (AList.lookup (op =) (Symtab.lookup_list arities a) c);

                val dom' = map2 (fn d => fn S' => weakens d S' ~~ S') dom Ss';

              in weaken (type_constructor a dom' c0, c0) c end)

          end

      | derive T S = weakens (type_variable T) S;

  in uncurry derive end;

(* witness_sorts *)

fun witness_sorts algebra types hyps sorts =

  let

    fun le S1 S2 = sort_le algebra (S1, S2);

    fun get_solved S2 (T, S1) = if le S1 S2 then SOME (T, S2) else NONE;

    fun get_hyp S2 S1 = if le S1 S2 then SOME (TFree ("'hyp", S1), S2) else NONE;

    fun mg_dom t S = SOME (mg_domain algebra t S) handle CLASS_ERROR _ => NONE;

    fun witn_sort _ [] solved_failed = (SOME (propT, []), solved_failed)

      | witn_sort path S (solved, failed) =

          if exists (le S) failed then (NONE, (solved, failed))

          else

            (case get_first (get_solved S) solved of

              SOME w => (SOME w, (solved, failed))

            | NONE =>

                (case get_first (get_hyp S) hyps of

                  SOME w => (SOME w, (w :: solved, failed))

                | NONE => witn_types path types S (solved, failed)))

    and witn_sorts path x = fold_map (witn_sort path) x

    and witn_types _ [] S (solved, failed) = (NONE, (solved, S :: failed))

      | witn_types path (t :: ts) S solved_failed =

          (case mg_dom t S of

            SOME SS =>

              (*do not descend into stronger args (achieving termination)*)

              if exists (fn D => le D S orelse exists (le D) path) SS then

                witn_types path ts S solved_failed

              else

                let val (ws, (solved', failed')) = witn_sorts (S :: path) SS solved_failed in

                  if forall is_some ws then

                    let val w = (Type (t, map (#1 o the) ws), S)

                    in (SOME w, (w :: solved', failed')) end

                  else witn_types path ts S (solved', failed')

                end

          | NONE => witn_types path ts S solved_failed);

  in map_filter I (#1 (witn_sorts [] sorts ([], []))) end;

end;