(* Copyright (C) 2012  G. Gonthier, B. Ziliani, A. Nanevski, D. Dreyer  This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.  This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.  You should have received a copy of the GNU General Public License along with this program.  If not, see <http://www.gnu.org/licenses/>. *)
From mathcomp
From LemmaOverloading
Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.
(* Exceptions are an equality type *)
Inductive exn : Type := exn_from_nat : nat -> exn.
Definition exn_to_nat (e : exn) : nat :=
let: exn_from_nat y := e in y.
Definition eqexn (e1 e2 : exn) : bool :=
match e1, e2 with exn_from_nat m, exn_from_nat n => m == n end.

Lemma eqexnP : Equality.axiom eqexn.
Canonical Structure exn_eqMixin := EqMixin eqexnP.