Add Arg_spec.of_result{,_map}

src/arg_spec.ml

@@ -71,3 +71,12 @@ let quote_args =
     | arg :: args -> quote :: arg :: loop quote args
   in
   fun quote args -> As (loop quote args)
+
+let of_result = function
+  | Ok x -> x
+  | Error e -> Dyn (fun _ -> raise e)
+
+let of_result_map res ~f =
+  match res with
+  | Ok    x -> f x
+  | Error e -> Dyn (fun _ -> raise e)

src/arg_spec.mli

@@ -46,3 +46,6 @@ val expand      : dir:Path.t -> 'a t list -> 'a -> string list * Path.Set.t
 
 (** [quote_args quote args] is [As \[quote; arg1; quote; arg2; ...\]] *)
 val quote_args : string -> string list -> _ t
+
+val of_result : ('a t, exn) result -> 'a t
+val of_result_map : ('a, exn) result -> f:('a -> 'b t) -> 'b t