feat(result): Added isError & isOk

Author: julian-siebert

src/main/java/gentle/Result.java

@@ -45,6 +45,28 @@ default Optional<T> asOptional() {
         };
     }
 
+    /**
+     * Returns whether this {@code Result} represents an error.
+     * <p>
+     * Equivalent to checking {@code instanceOf Err}.
+     *
+     * @return {@code true} if this is an {@link Err}, otherwise {@code false}
+     */
+    default boolean isError() {
+        return this instanceof Err<T,E>;
+    }
+
+    /**
+     * Returns whether this {@code Result} represents a successful value.
+     * <p>
+     * Equivalent to checking {@code instanceOf Ok}.
+     *
+     * @return {@code true} if this is an {@link Ok}, otherwise {@code false}
+     */
+    default boolean isOk() {
+        return this instanceof Ok<T,E>;
+    }
+
     /**
      * Transforms the success value using the given function, leaving errors unchanged.
      *