Add is_ok and is_error, simple predicates for testing a result. This is useful for tests or asserts

AUTHORS.adoc

@@ -16,3 +16,4 @@
 - Johannes Kloos
 - Geoff Gole (@gsg)
 - Roma Sokolov (@little-arhat)
+- Malcolm Matalka (`orbitz`)

src/core/CCResult.ml

@@ -98,6 +98,14 @@ let fold ~ok ~error x = match x with
   | Ok x -> ok x
   | Error s -> error s
 
+let is_ok = function
+  | Ok _ -> true
+  | Error _ -> false
+
+let is_error = function
+  | Ok _ -> false
+  | Error _ -> true
+
 (** {2 Wrappers} *)
 
 let guard f =

src/core/CCResult.mli

@@ -87,6 +87,16 @@ val fold : ok:('a -> 'b) -> error:('err -> 'b) -> ('a, 'err) t -> 'b
 (** [fold ~ok ~error e] opens [e] and, if [e = Ok x], returns
     [ok x], otherwise [e = Error s] and it returns [error s]. *)
 
+val is_ok : ('a, 'err) t -> bool
+(** Return true if Ok/
+
+    @since NEXT_RELEASE *)
+
+val is_error : ('a, 'err) t -> bool
+(** Return true if Error
+
+    @since NEXT_RELEASE *)
+
 (** {2 Wrappers} *)
 
 val guard : (unit -> 'a) -> ('a, exn) t