add Fut.is_done

src/fut.ml

@@ -28,6 +28,11 @@ let[@inline] peek self : _ option =
   | Done x -> Some x
   | Waiting _ -> None
 
+let[@inline] is_done self : bool =
+  match A.get self.st with
+  | Done _ -> true
+  | Waiting _ -> false
+
 exception Not_ready
 
 let[@inline] get_or_fail self =

src/fut.mli

@@ -75,6 +75,10 @@ val get_or_fail_exn : 'a t -> 'a
     @raise Not_ready if the future is not ready.
     @since 0.2 *)
 
+val is_done : _ t -> bool
+(** Is the future resolved? This is the same as [peek fut |> Option.is_some].
+    @since 0.2 *)
+
 (** {2 Combinators} *)
 
 val spawn : on:Pool.t -> (unit -> 'a) -> 'a t