(* -*- coq-prog-args: ("-emacs-U" "-R" "." "Prelude") -*- *)
(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(* Certified Haskell Prelude.
 * Author: Matthieu Sozeau
 * Institution: LRI, CNRS UMR 8623 - UniversitĂcopyright Paris Sud
 *              91405 Orsay, France *)

(* $Id: FSetAVL_prog.v 616 2007-08-08 12:28:10Z msozeau $ *)

Require Import Prelude.Monad.

Set Implicit Arguments.
Unset Strict Implicit.

Section Exception_Monad.
  Variable exn : Type.

  Inductive ex (A : Type) : Type := 
    | val : A -> ex A
    | raise : exn -> ex A.

  Implicit Arguments raise [A].

  Program Instance Monad ex :=
    unit A a := val a ;
    bind A B m f := 
      match m with
        | val x => f x
        | raise x => raise x
      end.
  
  Solve Obligations using intros ; destruct x ; auto.

  Definition try_with A (e : ex A) (catch : exn -> A) : A :=
    match e with
      | val x => x
      | raise ex => catch ex
    end.

End Exception_Monad.

Notation " 'try' e 'with' f 'end' " := (try_with e f) (at level 50).