diff --git a/libs/react/include/psemek/react/map.hpp b/libs/react/include/psemek/react/map.hpp
index dc997acd..e6fc3945 100644
--- a/libs/react/include/psemek/react/map.hpp
+++ b/libs/react/include/psemek/react/map.hpp
@@ -5,42 +5,53 @@
 namespace psemek::react
 {
 
-	template <typename F, typename ... Args>
-	auto map(F func, value<Args> ... args)
+	namespace detail
 	{
-		using R = decltype(func(std::declval<Args const &>()...));
 
-		auto node = std::make_shared<detail::node<R>>();
-		auto weak_node = std::weak_ptr{node};
+		template <typename F, typename ... Args>
+		auto map_impl(F func, value<Args> ... args)
+		{
+			using R = decltype(func(std::declval<Args const &>()...));
 
-		auto internal_subscriber = [weak_node]{
-			if (auto node = weak_node.lock())
-			{
-				node->cached_value = std::nullopt;
-				node->internal_signal();
-			}
-		};
+			auto node = std::make_shared<detail::node<R>>();
+			auto weak_node = std::weak_ptr{node};
 
-		auto external_subscriber = [weak_node](auto const &){
-			if (auto node = weak_node.lock())
-			{
-				if (!node->cached_value)
-					node->external_signal(node->value());
-			}
-		};
+			auto internal_subscriber = [weak_node]{
+				if (auto node = weak_node.lock())
+				{
+					node->cached_value = std::nullopt;
+					node->internal_signal();
+				}
+			};
 
-		auto internal_tokens = std::tuple{args.subscribe(detail::internal_tag{}, internal_subscriber)...};
-		auto external_tokens = std::tuple{args.subscribe(external_subscriber)...};
+			auto external_subscriber = [weak_node](auto const &){
+				if (auto node = weak_node.lock())
+				{
+					if (!node->cached_value)
+						node->external_signal(node->value());
+				}
+			};
 
-		node->getter = [
-			func = std::move(func),
-			internal_tokens = std::move(internal_tokens),
-			external_tokens = std::move(external_tokens),
-			args...]() -> R {
-			return func(*args...);
-		};
+			auto internal_tokens = std::tuple{args.subscribe(detail::internal_tag{}, internal_subscriber)...};
+			auto external_tokens = std::tuple{args.subscribe(external_subscriber)...};
 
-		return value<R>(detail::internal_tag{}, std::move(node));
+			node->getter = [
+				func = std::move(func),
+				internal_tokens = std::move(internal_tokens),
+				external_tokens = std::move(external_tokens),
+				args...]() -> R {
+				return func(*args...);
+			};
+
+			return value<R>(detail::internal_tag{}, std::move(node));
+		}
+
+	}
+
+	template <typename F, typename ... Args>
+	auto map(F func, Args && ... args)
+	{
+		return detail::map_impl(std::move(func), make_value(std::forward<Args>(args))...);
 	}
 
 }
diff --git a/libs/react/include/psemek/react/source.hpp b/libs/react/include/psemek/react/source.hpp
index afc99963..087647ea 100644
--- a/libs/react/include/psemek/react/source.hpp
+++ b/libs/react/include/psemek/react/source.hpp
@@ -9,6 +9,13 @@ namespace psemek::react
 	struct source
 		: value<T>
 	{
+		source(source const &) = default;
+		source(source &&) = default;
+
+		source()
+			: source(T{})
+		{}
+
 		source(T x)
 			: value<T>(detail::internal_tag{}, std::make_shared<detail::node<T>>())
 		{
@@ -22,12 +29,41 @@ namespace psemek::react
 			this->node_->internal_signal();
 			this->node_->external_signal(this->node_->value());
 		}
+
+		template <typename F>
+		void modify(F && f) const
+		{
+			set(f(this->node_->value()));
+		}
+
+		template <typename H, typename F>
+		source<H> modifier(H value, F && f)
+		{
+			std::weak_ptr weak_node = this->node_;
+
+			source<H> result(std::move(value));
+			this->node_->subscriptions.push_back(result.subscribe([weak_node, f = std::forward<F>(f)](H const & value) mutable {
+				if (auto node = weak_node.lock())
+				{
+					T x = f(node->value(), value);
+					node->cached_value = std::nullopt;
+					node->getter = [x = std::move(x)]() mutable { return std::move(x); };
+					node->internal_signal();
+					node->external_signal(node->value());
+				}
+			}));
+
+			return result;
+		}
 	};
 
 	template <>
 	struct source<void>
 		: value<void>
 	{
+		source(source const &) = default;
+		source(source &&) = default;
+
 		source()
 			: value<void>(detail::internal_tag{}, std::make_shared<detail::node<void>>())
 		{}
@@ -39,4 +75,10 @@ namespace psemek::react
 		}
 	};
 
+	template <typename T>
+	value<T> make_value(source<T> const & s)
+	{
+		return s;
+	}
+
 }
diff --git a/libs/react/include/psemek/react/value.hpp b/libs/react/include/psemek/react/value.hpp
index 1dea6948..9f4017eb 100644
--- a/libs/react/include/psemek/react/value.hpp
+++ b/libs/react/include/psemek/react/value.hpp
@@ -4,6 +4,7 @@
 
 #include <optional>
 #include <memory>
+#include <initializer_list>
 
 namespace psemek::react
 {
@@ -21,11 +22,12 @@ namespace psemek::react
 			util::signal<T> external_signal;
 			util::function<T()> getter;
 			std::optional<T> cached_value;
+			std::vector<std::shared_ptr<void>> subscriptions;
 
 			T const & value()
 			{
 				if (!cached_value)
-					cached_value = getter();
+					cached_value.emplace(getter());
 				return *cached_value;
 			}
 		};
@@ -52,15 +54,41 @@ namespace psemek::react
 			using type = void;
 		};
 
+		template <typename C>
+		constexpr bool is_container = requires { typename C::value_type; };
+
 	}
 
 	template <typename T>
 	struct value
 	{
+		value() = default;
+		value(value const &) = default;
+		value(value && other) = default;
+
+		template <typename ... Args, typename = std::enable_if_t<std::is_constructible_v<T, Args...>>>
+		value(Args && ... args)
+			: node_(std::make_shared<detail::node<T>>())
+		{
+			node_->cached_value.emplace(std::forward<Args>(args)...);
+		}
+
+		template <typename C = T, typename = typename C::value_type>
+		value(std::initializer_list<typename C::value_type> list)
+			: node_(std::make_shared<detail::node<T>>())
+		{
+			node_->cached_value.emplace(list);
+		}
+
 		value(detail::internal_tag, std::shared_ptr<detail::node<T>> node)
 			: node_(node)
 		{}
 
+		explicit operator bool() const
+		{
+			return static_cast<bool>(node_);
+		}
+
 		typename detail::node_value_type<T>::type operator *() const
 		{
 			return node_->value();
@@ -87,4 +115,16 @@ namespace psemek::react
 		std::shared_ptr<detail::node<T>> node_;
 	};
 
+	template <typename T>
+	value<T> make_value(T x)
+	{
+		return value<T>(std::move(x));
+	}
+
+	template <typename T>
+	value<T> make_value(value<T> const & v)
+	{
+		return v;
+	}
+
 }