diff --git a/include/sled/futures/detail/base_future.h b/include/sled/futures/detail/base_future.h
index bbaff54..55285cb 100644
--- a/include/sled/futures/detail/base_future.h
+++ b/include/sled/futures/detail/base_future.h
@@ -1,63 +1,208 @@
 #ifndef SLED_FUTURES_DETAIL_BASE_FUTURE_H
 #define SLED_FUTURES_DETAIL_BASE_FUTURE_H
-#include "sled/any.h"
+#include "sled/log/log.h"
+#include "sled/optional.h"
 #include "sled/synchronization/mutex.h"
 #include <memory>
 #include <type_traits>
 
 namespace sled {
 
-template<typename T>
-class Promise;
+namespace {
+enum class State {
+    kCancel,
+    kPending,
+    kTimeout,
+    kError,
+    kValue,
+};
+};
 
 template<typename T>
-class FutureState {
-public:
-    T Get()
+struct FutureState {
+    mutable sled::Mutex mutex;
+    mutable sled::ConditionVariable cond_var;
+
+    sled::optional<T> value;
+    std::exception_ptr error;
+
+    State state = State::kPending;
+
+    void AssertHasValue() const { ASSERT(state == State::kValue, "can't find value"); }
+
+    void AssertHasError() const { ASSERT(state == State::kError, "can't find error"); }
+
+    void AssertHasTimeout() const { ASSERT(state == State::kTimeout, "can't find timeout"); }
+
+    void Wait(sled::MutexLock *lock_ptr = nullptr) const
     {
-        sled::MutexLock lock(&mutex_);
-        cv_.Wait(&mutex_, [this]() { return done_; });
-        return sled::any_cast<T>(value_);
+        if (lock_ptr) {
+            if (state != State::kPending) { return; }
+            cond_var.Wait(*lock_ptr, [this] { return state != State::kPending; });
+        } else {
+            sled::MutexLock lock(&mutex);
+            if (state != State::kPending) { return; }
+            cond_var.Wait(lock, [this] { return state != State::kPending; });
+        }
     }
 
     void SetError(std::exception_ptr e)
     {
-        sled::MutexLock lock(&mutex_);
-        value_ = e;
-        done_ = true;
-    };
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        error = std::move(e);
+        state = State::kError;
+        cond_var.NotifyAll();
+    }
 
-    template<typename U = T>
-    typename std::enable_if<!std::is_void<T>::value && std::is_convertible<U, T>::value>::type SetValue(U &&value)
+    void SetTimeout()
     {
-        sled::MutexLock lock(&mutex_);
-        value_ = static_cast<T>(std::forward<U>(value));
-        done_ = true;
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        state = State::kTimeout;
+        cond_var.NotifyAll();
     }
 
     template<typename U = T>
-    typename std::enable_if<std::is_void<T>::value>::type SetValue(U &&value)
+    typename std::enable_if<std::is_convertible<U, T>::value>::type SetValue(U &&val)
     {
-        sled::MutexLock lock(&mutex_);
-        done_ = true;
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        value = std::forward<U>(val);
+        state = State::kValue;
+        cond_var.NotifyAll();
+    }
+};
+
+template<>
+struct FutureState<void> {
+    mutable sled::Mutex mutex;
+    mutable sled::ConditionVariable cond_var;
+
+    std::exception_ptr error;
+
+    State state = State::kPending;
+
+    void AssertHasValue() const { ASSERT(state == State::kValue, "can't find value"); }
+
+    void AssertHasError() const { ASSERT(state == State::kError, "can't find error"); }
+
+    void AssertHasTimeout() const { ASSERT(state == State::kTimeout, "can't find timeout"); }
+
+    void Wait(sled::MutexLock *lock_ptr = nullptr) const
+    {
+        if (lock_ptr) {
+            if (state != State::kPending) { return; }
+            cond_var.Wait(*lock_ptr, [this] { return state != State::kPending; });
+        } else {
+            sled::MutexLock lock(&mutex);
+            if (state != State::kPending) { return; }
+            cond_var.Wait(lock, [this] { return state != State::kPending; });
+        }
     }
 
-private:
-    sled::Mutex mutex_;
-    sled::ConditionVariable cv_;
-    sled::any value_;
-    bool done_{false};
+    void SetTimeout()
+    {
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        state = State::kTimeout;
+        cond_var.NotifyAll();
+    }
+
+    void SetError(std::exception_ptr e)
+    {
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        error = std::move(e);
+        state = State::kError;
+        cond_var.NotifyAll();
+    }
+
+    void SetValue()
+    {
+        sled::MutexLock lock(&mutex);
+        if (state == State::kCancel) { return; }
+        ASSERT(state == State::kPending, "state must be kPending");
+        state = State::kValue;
+        cond_var.NotifyAll();
+    }
 };
 
 template<typename T>
-class BaseFuture {
+class Future {
 public:
-    template<typename T>
-    T Get() const
+    // using ValueType = typename std::remove_reference<T>::type;
+    Future(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
+
+    T Get() const &
     {
-        return state_->Get();
+        sled::MutexLock lock(&state_->mutex);
+        state_->Wait(&lock);
+        state_->AssertHasValue();
+        return state_->value.value();
     }
 
+    T &Get() &
+    {
+        sled::MutexLock lock(&state_->mutex);
+        state_->Wait(&lock);
+        state_->AssertHasValue();
+        return state_->value.value();
+    }
+
+    T &&Get() &&
+    {
+        sled::MutexLock lock(&state_->mutex);
+        state_->Wait(&lock);
+        state_->AssertHasValue();
+        return std::move(state_->value.value());
+    }
+
+private:
+    std::shared_ptr<FutureState<T>> state_;
+};
+
+template<>
+class Future<void> {
+public:
+    Future(std::shared_ptr<FutureState<void>> state) : state_(std::move(state)) {}
+
+    void Wait() const { state_->Wait(); }
+
+    void Get() const { Wait(); }
+
+protected:
+    std::shared_ptr<FutureState<void>> state_;
+};
+
+template<typename T>
+class Promise {
+public:
+    Promise() : state_(new FutureState<T>()) {}
+
+    Future<T> GetFuture() const { return Future<T>(state_); }
+
+    template<typename U = T>
+    typename std::enable_if<!std::is_void<U>::value && std::is_convertible<U, T>::value>::type SetValue(U &&val)
+    {
+        state_->SetValue(val);
+    }
+
+    template<typename U = T>
+    typename std::enable_if<std::is_void<U>::value>::type SetValue()
+    {
+        state_->SetValue();
+    }
+
+    void SetError(std::exception_ptr e) { state_->SetError(e); }
+
+    void SetTimeout() { state_->SetTimeout(); }
+
 private:
     std::shared_ptr<FutureState<T>> state_;
 };
diff --git a/include/sled/futures/detail/just.h b/include/sled/futures/detail/just.h
new file mode 100644
index 0000000..58ac377
--- /dev/null
+++ b/include/sled/futures/detail/just.h
@@ -0,0 +1,39 @@
+#ifndef SLED_FUTURES_DETAIL_JUST_H
+#define SLED_FUTURES_DETAIL_JUST_H
+
+#include <memory>
+
+namespace sled {
+namespace detail {
+
+template<typename T, typename R>
+struct JustOperation {
+    T value;
+    R receiver;
+
+    void Start() { receiver.SetValue(std::move(value)); }
+
+    void Stop() { receiver.SetStopped(); }
+};
+
+template<typename T>
+struct JustSender {
+    T value;
+
+    template<typename R>
+    JustOperation<T, R> Connect(R receiver)
+    {
+        return {value, receiver};
+    }
+};
+
+template<typename T>
+JustSender<T>
+Just(T value)
+{
+    return {value};
+}
+
+}// namespace detail
+}// namespace sled
+#endif//  SLED_FUTURES_DETAIL_JUST_H
diff --git a/include/sled/futures/detail/retry.h b/include/sled/futures/detail/retry.h
new file mode 100644
index 0000000..d82736c
--- /dev/null
+++ b/include/sled/futures/detail/retry.h
@@ -0,0 +1,120 @@
+#ifndef SLED_FUTURES_DETAIL_RETRY_H
+#define SLED_FUTURES_DETAIL_RETRY_H
+
+#include "sled/log/log.h"
+#include "sled/synchronization/mutex.h"
+#include "traits.h"
+#include <memory>
+
+namespace sled {
+namespace detail {
+
+namespace {
+struct RetryState {
+    enum State { kPending, kDone, kRetry };
+
+    sled::Mutex mutex;
+    sled::ConditionVariable cv;
+    int retry_count = 0;
+    State state = kPending;
+};
+}// namespace
+
+template<typename R>
+struct RetryReceiver {
+    std::shared_ptr<RetryState> state;
+    R receiver;
+    bool stopped = false;
+
+    template<typename U>
+    void SetValue(U &&val)
+    {
+        {
+            sled::MutexLock lock(&state->mutex);
+            if (stopped) { return; }
+            state->state = RetryState::kDone;
+            state->cv.NotifyAll();
+        }
+        receiver.SetValue(std::forward<U>(val));
+    }
+
+    void SetError(std::exception_ptr e)
+    {
+        // notify
+        {
+            sled::MutexLock lock(&state->mutex);
+            if (stopped) { return; }
+            if (state->retry_count > 0) {
+                --state->retry_count;
+                state->state = RetryState::kRetry;
+                return;
+            } else {
+                state->state = RetryState::kDone;
+                state->cv.NotifyAll();
+            }
+        }
+        receiver.SetError(e);
+    }
+
+    void SetStopped()
+    {
+        {
+            sled::MutexLock lock(&state->mutex);
+            if (stopped) { return; }
+            stopped = true;
+            state->state = RetryState::kDone;
+            state->cv.NotifyAll();
+        }
+        receiver.SetStopped();
+    }
+};
+
+template<typename S, typename R>
+struct RetryOperation {
+    int retry_count;
+    std::shared_ptr<RetryState> state;
+    ConnectResultT<S, R> op;
+
+    void Start()
+    {
+        {
+            sled::MutexLock lock(&state->mutex);
+            state->retry_count = retry_count;
+            state->state = RetryState::kPending;
+        }
+        do {
+            op.Start();
+            sled::MutexLock lock(&state->mutex);
+            state->cv.Wait(lock, [this] { return state->state != RetryState::kPending; });
+            if (state->state == RetryState::kDone) { break; }
+            state->state = RetryState::kPending;
+        } while (true);
+    }
+
+    void Stop() { op.Stop(); }
+};
+
+template<typename S>
+struct RetrySender {
+    S sender;
+    int retry_count;
+
+    template<typename R>
+    RetryOperation<S, RetryReceiver<R>> Connect(R receiver)
+    {
+        auto state = std::make_shared<RetryState>();
+        auto op = sender.Connect(RetryReceiver<R>{state, receiver});
+        return {retry_count, state, op};
+    }
+};
+
+template<typename S>
+RetrySender<S>
+Retry(S sender, int retry_count)
+{
+    return {sender, retry_count};
+}
+
+}// namespace detail
+}// namespace sled
+#endif//  SLED_FUTURES_DETAIL_RETRY_H
diff --git a/include/sled/futures/detail/then.h b/include/sled/futures/detail/then.h
new file mode 100644
index 0000000..811941b
--- /dev/null
+++ b/include/sled/futures/detail/then.h
@@ -0,0 +1,71 @@
+#ifndef SLED_FUTURES_DETAIL_THEN_H
+#define SLED_FUTURES_DETAIL_THEN_H
+
+#include "traits.h"
+#include <memory>
+
+namespace sled {
+namespace detail {
+
+template<typename R, typename F>
+struct ThenReceiver {
+    R receiver;
+    F func;
+    bool stopped = false;
+
+    template<typename U>
+    void SetValue(U &&val)
+    {
+        if (stopped) { return; }
+        try {
+            receiver.SetValue(func(std::forward<U>(val)));
+        } catch (...) {
+            SetError(std::current_exception());
+        }
+    }
+
+    void SetError(std::exception_ptr e)
+    {
+        if (stopped) { return; }
+        receiver.SetError(e);
+    }
+
+    void SetStopped()
+    {
+        if (stopped) { return; }
+        stopped = true;
+        receiver.SetStopped();
+    }
+};
+
+template<typename S, typename R>
+struct ThenOperation {
+    ConnectResultT<S, R> op;
+
+    void Start() { op.Start(); }
+
+    void Stop() { op.Stop(); }
+};
+
+template<typename S, typename F>
+struct ThenSender {
+    S sender;
+    F func;
+
+    template<typename R>
+    ThenOperation<S, ThenReceiver<R, F>> Connect(R receiver)
+    {
+        return {sender.Connect(ThenReceiver<R, F>{receiver, func})};
+    }
+};
+
+template<typename S, typename F>
+ThenSender<S, F>
+Then(S sender, F &&func)
+{
+    return {sender, std::forward<F>(func)};
+}
+
+}// namespace detail
+}// namespace sled
+#endif//  SLED_FUTURES_DETAIL_THEN_H
diff --git a/include/sled/futures/detail/traits.h b/include/sled/futures/detail/traits.h
new file mode 100644
index 0000000..332f930
--- /dev/null
+++ b/include/sled/futures/detail/traits.h
@@ -0,0 +1,18 @@
+#ifndef SLED_FUTURES_DETAIL_TRAITS_H
+#define SLED_FUTURES_DETAIL_TRAITS_H
+
+#include <type_traits>
+
+namespace sled {
+namespace detail {
+template<typename S, typename R>
+struct ConnectResult {
+    typedef decltype(std::declval<S>().Connect(std::declval<R>())) type;
+};
+
+template<typename S, typename R>
+using ConnectResultT = typename ConnectResult<S, R>::type;
+
+}// namespace detail
+}// namespace sled
+#endif// SLED_FUTURES_DETAIL_TRAITS_H
diff --git a/include/sled/futures/detail/via.h b/include/sled/futures/detail/via.h
new file mode 100644
index 0000000..7aa8990
--- /dev/null
+++ b/include/sled/futures/detail/via.h
@@ -0,0 +1,72 @@
+#ifndef SLED_FUTURES_DETAIL_VIA_H
+#define SLED_FUTURES_DETAIL_VIA_H
+#include "traits.h"
+#include <exception>
+#include <functional>
+#include <memory>
+
+namespace sled {
+namespace detail {
+template<typename R, typename F>
+struct ViaReceiver {
+    R receiver;
+    F schedule;
+    bool stopped = false;
+
+    template<typename U>
+    void SetValue(U &&val)
+    {
+        if (stopped) { return; }
+        try {
+            auto func = std::bind(&R::SetValue, &receiver, std::forward<U>(val));
+            schedule(std::move(func));
+        } catch (...) {
+            SetError(std::current_exception());
+        }
+    }
+
+    void SetError(std::exception_ptr e)
+    {
+        if (stopped) { return; }
+        receiver.SetError(e);
+    }
+
+    void SetStopped()
+    {
+        if (stopped) { return; }
+        stopped = true;
+        receiver.SetStopped();
+    }
+};
+
+template<typename S, typename R>
+struct ViaOperation {
+    ConnectResultT<S, R> op;
+
+    void Start() { op.Start(); }
+
+    void Stop() { op.Stop(); }
+};
+
+template<typename S, typename F>
+struct ViaSender {
+    S sender;
+    F schedule;
+
+    template<typename R>
+    ViaOperation<S, ViaReceiver<R, F>> Connect(R receiver)
+    {
+        return {sender.Connect(ViaReceiver<R, F>{receiver, schedule})};
+    }
+};
+
+template<typename S, typename F>
+ViaSender<S, F>
+Via(S sender, F &&schedule)
+{
+    return {sender, std::forward<F>(schedule)};
+}
+
+}// namespace detail
+}// namespace sled
+#endif// SLED_FUTURES_DETAIL_VIA_H
diff --git a/include/sled/sled.h b/include/sled/sled.h
index 5c8df03..d3a06d0 100644
--- a/include/sled/sled.h
+++ b/include/sled/sled.h
@@ -11,7 +11,7 @@
 #include "sled/filesystem/temporary_file.h"
 
 // futures
-#include "sled/futures/promise.h"
+// #include "sled/futures/promise.h"
 
 // lang
 #include "lang/attributes.h"