end.
Notation "a >>= b" := (@orErrorBind _ a _ b) (at level 20).
+Open Scope string_scope.
+Definition orErrorBindWithMessage {T:Type} (oe:OrError T) {Q:Type} (f:T -> OrError Q) err_msg :=
+ match oe with
+ | Error s => Error (err_msg +++ eol +++ " " +++ s)
+ | OK t => f t
+ end.
+
+Notation "a >>=[ S ] b" := (@orErrorBindWithMessage _ a _ b S) (at level 20).
+
+Definition addErrorMessage s {T} (x:OrError T) :=
+ x >>=[ s ] (fun y => OK y).
+
Inductive Indexed {T:Type}(f:T -> Type) : ???T -> Type :=
| Indexed_Error : forall error_message:string, Indexed f (Error error_message)
| Indexed_OK : forall t, f t -> Indexed f (OK t)