diff --git a/source/mijin/container/optional.hpp b/source/mijin/container/optional.hpp
index 4e9148d..fb48971 100644
--- a/source/mijin/container/optional.hpp
+++ b/source/mijin/container/optional.hpp
@@ -8,6 +8,7 @@
 #include <utility>
 #include "../debug/assert.hpp"
 #include "../util/concepts.hpp"
+#include "../util/traits.hpp"
 
 namespace mijin
 {
@@ -154,6 +155,44 @@ public:
     [[nodiscard]] inline const std::remove_reference_t<TValue>& get() const noexcept;
     [[nodiscard]] constexpr bool empty() const noexcept { return storage_.empty(); }
     inline void reset() noexcept;
+
+
+    template<typename TCallable, typename TErrorCallable = int>
+    auto then(TCallable&& onSuccess, TErrorCallable&& onError = 0)
+    {
+        using result_t = std::invoke_result_t<TCallable, std::add_rvalue_reference_t<TValue>>;
+
+        if constexpr (std::is_same_v<result_t, void>)
+        {
+            if (!empty())
+            {
+                std::invoke(std::forward<TCallable>(onSuccess), get());
+            }
+            else if constexpr (!std::is_same_v<TErrorCallable, int>)
+            {
+                std::invoke(std::forward<TErrorCallable>(onError));
+            }
+        }
+        else if constexpr (requires(result_t obj) { {obj == NULL_OPTIONAL} -> std::convertible_to<bool>; })
+        {
+            if (!empty())
+            {
+                return std::invoke(std::forward<TCallable>(onSuccess), get());
+            }
+            else
+            {
+                if constexpr (!std::is_same_v<TErrorCallable, int>)
+                {
+                    std::invoke(std::forward<TErrorCallable>(onError));
+                }
+                return NULL_OPTIONAL;
+            }
+        }
+        else
+        {
+            static_assert(always_false_v<TCallable>, "Callable must produce void or optional type.");
+        }
+    }
 };
 
 //