signature QUOTIENT =

sig

  exception LIFT_MATCH of string

  val quotient_type: ((binding * mixfix) * (typ * term)) list -> Proof.context -> Proof.state

  val quotient_type_cmd: (((bstring * mixfix) * string) * string) list -> Proof.context -> Proof.state

end;

structure Quotient: QUOTIENT =

struct

exception LIFT_MATCH of string

(* wrappers for define, note and theorem_i *)

fun define (name, mx, rhs) lthy =

let

  val ((rhs, (_ , thm)), lthy') =

     Local_Theory.define ((name, mx), (Attrib.empty_binding, rhs)) lthy

in

  ((rhs, thm), lthy')

end

fun note (name, thm, attrs) lthy =

let

  val ((_,[thm']), lthy') = Local_Theory.note ((name, attrs), [thm]) lthy

in

  (thm', lthy')

end

fun internal_attr at = Attrib.internal (K at)

fun theorem after_qed goals ctxt =

let

  val goals' = map (rpair []) goals

  fun after_qed' thms = after_qed (the_single thms)

in 

  Proof.theorem_i NONE after_qed' [goals'] ctxt

end

(* definition of quotient types *)

(********************************)

(* constructs the term lambda (c::rty => bool). EX (x::rty). c = rel x *)

fun typedef_term rel rty lthy =

let

  val [x, c] = [("x", rty), ("c", HOLogic.mk_setT rty)]

               |> Variable.variant_frees lthy [rel]

               |> map Free

in

  lambda c

    (HOLogic.exists_const rty $

       lambda x (HOLogic.mk_eq (c, (rel $ x))))

end

(* makes the new type definitions and proves non-emptyness*)

fun typedef_make (qty_name, mx, rel, rty) lthy =

let

  val typedef_tac =

     EVERY1 [rewrite_goal_tac @{thms mem_def},

             rtac @{thm exI},

             rtac @{thm exI},

             rtac @{thm refl}]

  val tfrees = map fst (Term.add_tfreesT rty [])

in

  Local_Theory.theory_result

    (Typedef.add_typedef false NONE

       (qty_name, tfrees, mx)

         (typedef_term rel rty lthy)

           NONE typedef_tac) lthy

end

(* tactic to prove the QUOT_TYPE theorem for the new type *)

fun typedef_quot_type_tac equiv_thm (typedef_info: Typedef.info) =

let

  val unfold_mem = MetaSimplifier.rewrite_rule [@{thm mem_def}]

  val rep_thm = #Rep typedef_info |> unfold_mem

  val rep_inv = #Rep_inverse typedef_info

  val abs_inv = #Abs_inverse typedef_info |> unfold_mem

  val rep_inj = #Rep_inject typedef_info

in

  EVERY1 [rtac @{thm QUOT_TYPE.intro},

          rtac equiv_thm,

          rtac rep_thm,

          rtac rep_inv,

          rtac abs_inv,

          rtac @{thm exI}, 

          rtac @{thm refl},

          rtac rep_inj]

end

(* proves the QUOT_TYPE theorem *)

fun typedef_quot_type_thm (rel, abs, rep, equiv_thm, typedef_info) lthy =

let

  val quot_type_const = Const (@{const_name "QUOT_TYPE"}, dummyT)

  val goal = HOLogic.mk_Trueprop (quot_type_const $ rel $ abs $ rep)

             |> Syntax.check_term lthy

in

  Goal.prove lthy [] [] goal

    (K (typedef_quot_type_tac equiv_thm typedef_info))

end

(* proves the quotient theorem *)

fun typedef_quotient_thm (rel, abs, rep, abs_def, rep_def, quot_type_thm) lthy =

let

  val quotient_const = Const (@{const_name "Quotient"}, dummyT)

  val goal = HOLogic.mk_Trueprop (quotient_const $ rel $ abs $ rep)

             |> Syntax.check_term lthy

  val typedef_quotient_thm_tac =

    EVERY1 [K (rewrite_goals_tac [abs_def, rep_def]),

            rtac @{thm QUOT_TYPE.Quotient},

            rtac quot_type_thm]

in

  Goal.prove lthy [] [] goal

    (K typedef_quotient_thm_tac)

end

(* main function for constructing the quotient type *)

fun mk_typedef_main (((qty_name, mx), (rty, rel)), equiv_thm) lthy =

let

  (* generates typedef *)

  val ((_, typedef_info), lthy1) = typedef_make (qty_name, mx, rel, rty) lthy

  (* abs and rep functions *)

  val abs_ty = #abs_type typedef_info

  val rep_ty = #rep_type typedef_info

  val abs_name = #Abs_name typedef_info

  val rep_name = #Rep_name typedef_info

  val abs = Const (abs_name, rep_ty --> abs_ty)

  val rep = Const (rep_name, abs_ty --> rep_ty)

  (* ABS and REP definitions *)

  val ABS_const = Const (@{const_name "QUOT_TYPE.abs"}, dummyT )

  val REP_const = Const (@{const_name "QUOT_TYPE.rep"}, dummyT )

  val ABS_trm = Syntax.check_term lthy1 (ABS_const $ rel $ abs)

  val REP_trm = Syntax.check_term lthy1 (REP_const $ rep)

  val ABS_name = Binding.prefix_name "abs_" qty_name

  val REP_name = Binding.prefix_name "rep_" qty_name

  val (((ABS, ABS_def), (REP, REP_def)), lthy2) =

         lthy1 |> define (ABS_name, NoSyn, ABS_trm)

               ||>> define (REP_name, NoSyn, REP_trm)

  (* quot_type theorem *)

  val quot_thm = typedef_quot_type_thm (rel, abs, rep, equiv_thm, typedef_info) lthy2

  val quot_thm_name = Binding.prefix_name "QUOT_TYPE_" qty_name

  (* quotient theorem *)

  val quotient_thm = typedef_quotient_thm (rel, ABS, REP, ABS_def, REP_def, quot_thm) lthy2

  val quotient_thm_name = Binding.prefix_name "Quotient_" qty_name

  (* storing the quot-info *)

  val qty_str = fst (Term.dest_Type abs_ty)

  val lthy3 = quotdata_update qty_str 

               (Logic.varifyT abs_ty, Logic.varifyT rty, rel, equiv_thm) lthy2  

  (* FIXME: varifyT should not be used *)

  (* FIXME: the relation needs to be a string, since its type needs *)

  (* FIXME: to recalculated in for example REGULARIZE *)

in

  lthy3

  |> note (quot_thm_name, quot_thm, [])

  ||>> note (quotient_thm_name, quotient_thm, [internal_attr quotient_rules_add])

  ||>> note (Binding.suffix_name "_equivp" qty_name, equiv_thm, [internal_attr equiv_rules_add])

end

(* interface and syntax setup *)

(* the ML-interface takes a list of 4-tuples consisting of  *)

(*                                                          *)

(* - the name of the quotient type                          *)

(* - its mixfix annotation                                  *)

(* - the type to be quotient                                *)

(* - the relation according to which the type is quotient   *)

fun quotient_type quot_list lthy = 

let

  fun mk_goal (rty, rel) =

  let

    val equivp_ty = ([rty, rty] ---> @{typ bool}) --> @{typ bool}

  in 

    HOLogic.mk_Trueprop (Const (@{const_name equivp}, equivp_ty) $ rel)

  end

  val goals = map (mk_goal o snd) quot_list

  fun after_qed thms lthy =

    fold_map mk_typedef_main (quot_list ~~ thms) lthy |> snd

in

  theorem after_qed goals lthy

end

fun quotient_type_cmd spec lthy = 

let

  fun parse_spec (((qty_str, mx), rty_str), rel_str) =

  let

    val qty_name = Binding.name qty_str

    val rty = Syntax.read_typ lthy rty_str

    val rel = Syntax.read_term lthy rel_str 

  in

    ((qty_name, mx), (rty, rel))

  end

in

  quotient_type (map parse_spec spec) lthy

end

val quotspec_parser = 

    OuterParse.and_list1

     (OuterParse.short_ident -- OuterParse.opt_infix -- 

       (OuterParse.$$$ "=" |-- OuterParse.typ) -- 

         (OuterParse.$$$ "/" |-- OuterParse.term))

val _ = OuterKeyword.keyword "/"

val _ = 

    OuterSyntax.local_theory_to_proof "quotient" 

      "quotient type definitions (requires equivalence proofs)"

         OuterKeyword.thy_goal (quotspec_parser >> quotient_type_cmd)

end; (* structure *)

open Quotient