Raise Failure in Kdl.L.{get,set}_exn

Use failwith instead of Option.get

src/kdl.mli

@@ -221,10 +221,12 @@ module L : sig
   (** Run the setter ([lens.set]). *)
 
   val get_exn : 'a -> ('a, 'b) lens -> 'b
-  (** [get_exn a l] is [Option.get (get a l)]. *)
+  (** [get_exn a l] is a raising version of [get a l].
+      @raise Failure *)
 
   val set_exn : 'a -> 'b -> ('a, 'b) lens -> 'a
-  (** [set_exn a v l] is [Option.get (set a v l)]. *)
+  (** [set_exn a v l] is a raising version of [set a v l].
+      @raise Failure *)
 
   val (.@()) : 'a -> ('a, 'b) lens -> 'b option
   (** [(.@())] is an indexing operator for [get]. *)

src/lens.ml

@@ -11,9 +11,17 @@ let get a lens = lens.get a
 
 let set a v lens = lens.set v a
 
-let get_exn a lens = Option.get @@ lens.get a
+let error () = failwith "Lens failed to match"
 
-let set_exn a v lens = Option.get @@ lens.set v a
+let get_exn a lens =
+  match lens.get a with
+  | Some v -> v
+  | None -> error ()
+
+let set_exn a v lens =
+  match lens.set v a with
+  | Some v -> v
+  | None -> error ()
 
 (* update can be added to the definition of [lens] to increase performance with
    more specialized implementations *)