*io.Promise

x/io/README.md

@@ -36,9 +36,8 @@ async function asyncCall(): Promise<string> {
   return `AsyncCall: ${result}`;
 }
 
-async function asyncCall2(): Promise<string> {
+function asyncCall2(): Promise<string> {
-  const result = await resolveAfter1Second();
+  return resolveAfter1Second();
-  return `AsyncCall2: ${result}`;
 }
 
 function asyncCall3(): void {
@@ -92,9 +91,8 @@ async def async_call() -> str:
     result = await resolve_after_1_second()
     return f"AsyncCall: {result}"
 
-async def async_call2() -> str:
+def async_call2() -> asyncio.Task:
-    result = await resolve_after_1_second()
+    return resolve_after_1_second()
-    return f"AsyncCall2: {result}"
 
 def async_call3() -> None:
     asyncio.create_task(print_after_1_second())
@@ -139,7 +137,9 @@ async fn name(param0: Type) -> ReturnType {
 Example:
 
 ```rust
-use tokio::time::{sleep, Duration};
+use std::time::Duration;
+use tokio::time::sleep;
+use std::future::Future;
 
 async fn resolve_after_1_second() -> String {
     sleep(Duration::from_secs(1)).await;
@@ -151,9 +151,8 @@ async fn async_call() -> String {
     format!("AsyncCall: {}", result)
 }
 
-async fn async_call2() -> String {
+fn async_call2() -> impl Future<Output = String> {
-    let result = resolve_after_1_second().await;
+    resolve_after_1_second()
-    format!("AsyncCall2: {}", result)
 }
 
 fn async_call3() {
@@ -177,7 +176,7 @@ async fn main() {
     async_call3();
 
     // Wait for AsyncCall3 to complete
-    sleep(Duration::from_secs(1)).await;
+    sleep(Duration::from_secs(2)).await;
 
     println!("Main function completed");
 }
@@ -216,10 +215,9 @@ class Program
         return $"AsyncCall: {result}";
     }
 
-    static async Task<string> AsyncCall2()
+    static Task<string> AsyncCall2()
     {
-        string result = await ResolveAfter1Second();
+        return ResolveAfter1Second();
-        return $"AsyncCall2: {result}";
     }
 
     static void AsyncCall3()
@@ -286,8 +284,7 @@ cppcoro::task<std::string> asyncCall() {
 }
 
 cppcoro::task<std::string> asyncCall2() {
-    auto result = co_await resolveAfter1Second();
+    return resolveAfter1Second();
-    co_return "AsyncCall2: " + result;
 }
 
 cppcoro::task<void> asyncCall3() {
@@ -323,3 +320,90 @@ int main() {
     return 0;
 }
 ```
+
+## Common concepts
+
+### Promise, Future, Task, and Coroutine
+
+- **Promise**: An object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It is used to produce a value that will be consumed by a `Future`.
+
+- **Future**: An object that represents the result of an asynchronous operation. It is used to obtain the value produced by a `Promise`.
+
+- **Task**: A unit of work that can be scheduled and executed asynchronously. It is a higher-level abstraction that combines a `Promise` and a `Future`.
+
+- **Coroutine**: A special type of function that can suspend its execution and return control to the caller without losing its state. It can be resumed later, allowing for asynchronous programming.
+
+### `async`, `await` and similar keywords
+
+- **`async`**: A keyword used to define a function that returns a `Promise` or `Task`. It allows the function to pause its execution and resume later.
+
+- **`await`**: A keyword used to pause the execution of an `async` function until a `Promise` or `Task` is resolved. It unwraps the value of the `Promise` or `Task` and allows the function to continue.
+
+- **`co_return`**: A keyword used in C++ coroutines to return a value from a coroutine. It is similar to `return` but is used in coroutines to indicate that the coroutine has completed. It's similar to `return` in `async` functions in other languages that boxes the value into a `Promise` or `Task`.
+
+`async/await` and similar constructs provide a more readable and synchronous-like way of writing asynchronous code, it hides the type of `Promise`/`Future`/`Task` from the user and allows them to focus on the logic of the code.
+
+### Executing Multiple Async Operations Concurrently
+
+To run multiple promises concurrently, JavaScript provides `Promise.all`, `Promise.allSettled` and `Promise.any`, Python provides `asyncio.gather`, Rust provides `tokio::try_join`, C# provides `Task.WhenAll`, and C++ provides `cppcoro::when_all`.
+
+In some situations, you may want to get the first result of multiple async operations. JavaScript provides `Promise.race` to get the first result of multiple promises. Python provides `asyncio.wait` to get the first result of multiple coroutines. Rust provides `tokio::select!` to get the first result of multiple futures. C# provides `Task.WhenAny` to get the first result of multiple tasks. C++ provides `cppcoro::when_any` to get the first result of multiple tasks. Those functions are very simular to `select` in Go.
+
+### Error Handling
+
+`await` commonly unwraps the value of a `Promise` or `Task`, but it also propagates errors. If the `Promise` or `Task` is rejected or throws an error, the error will be thrown in the `async` function by the `await` keyword. You can use `try/catch` blocks to handle errors in `async` functions.
+
+## Common patterns
+
+- `async` keyword hides the types of `Promise`/`Future`/`Task` in the function signature in Python and Rust, but not in JavaScript, C#, and C++.
+- `await` keyword unwraps the value of a `Promise`/`Future`/`Task`.
+- `return` keyword boxes the value into a `Promise`/`Future`/`Task` if it's not already.
+
+## Design considerations in LLGo
+
+- Don't introduce `async`/`await` keywords to compatible with Go compiler.
+- For performance reason don't implement async functions with goroutines
+
+## Design
+
+```go
+func resolveAfter1Second() Promise[string] {
+  return Async(func (context) {
+    context.ScheduleAfter(1 * time.Second, func() {
+      context.Resolve("Resolved after 1 second")
+    })
+  })
+}
+
+func asyncCall() Promise[string] {
+  return Async(resolveAfter1Second().Await())
+}
+
+func asyncCall2() Promise[string] {
+  return resolveAfter1Second()
+}
+
+func asyncCall3() {
+  resolveAfter1Second().Then(func(result string) {
+    fmt.Println("AsyncCall3: " + result)
+  })
+}
+
+func asyncMain() {
+  fmt.Println("Starting AsyncCall")
+  result1 := asyncCall().Await()
+  fmt.Println(result1)
+
+  fmt.Println("Starting AsyncCall2")
+  result2 := asyncCall2().Await()
+  fmt.Println(result2)
+
+  fmt.Println("Starting AsyncCall3")
+  asyncCall3()
+
+  // Wait for AsyncCall3 to complete
+  time.Sleep(2 * time.Second)
+
+  fmt.Println("Main function completed")
+}
+```

x/io/_demo/asyncdemo/async.go

@@ -1,23 +1,108 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"time"
 
 	"github.com/goplus/llgo/x/io"
 )
 
-var GetUser = io.Async[any](func(string) any {
+type Response struct {
-	panic("todo: GetUser")
+	StatusCode int
-})
 
-var GetScore = io.Async[float64](func() float64 {
+	mockBody string
+}
+
+func (r *Response) mock(body string) {
+	r.mockBody = body
+}
+
+func (r *Response) Text() *io.Promise[string] {
+	return io.NewPromise[string](func(resolve func(string, error)) {
+		resolve(r.mockBody, nil)
+	})
+}
+
+func HttpGet(url string, callback func(resp *Response, err error)) {
+	panic("todo: Get")
+}
+
+func AsyncHttpGet(url string) io.AsyncCall[*Response] {
+	return io.NewPromise[*Response](func(resolve func(*Response, error)) {
+		HttpGet(url, resolve)
+	})
+}
+
+type User struct {
+	Name string
+}
+
+func GetUser(uid string) io.AsyncCall[User] {
+	return io.NewPromise[User](func(resolve func(User, error)) {
+		resp, err := io.Await(AsyncHttpGet("http://example.com/user/" + uid))
+		if err != nil {
+			resolve(User{}, err)
+			return
+		}
+
+		if resp.StatusCode != 200 {
+			resolve(User{}, fmt.Errorf("http status code: %d", resp.StatusCode))
+			return
+		}
+
+		resp.mock(`{"name":"Alice"}`)
+
+		body, err := io.Await[string](resp.Text())
+		if err != nil {
+			resolve(User{}, err)
+			return
+		}
+		user := User{}
+		if err := json.Unmarshal([]byte(body), &user); err != nil {
+			resolve(User{}, err)
+			return
+		}
+
+		resolve(user, nil)
+	})
+}
+
+// func GetUser1(uid string) (resolve io.AsyncCall[User]) {
+// 	resp, err := io.Await(AsyncHttpGet("http://example.com/user/" + uid))
+// 	if err != nil {
+// 		resolve(User{}, err)
+// 		return
+// 	}
+
+// 	if resp.StatusCode != 200 {
+// 		resolve(User{}, fmt.Errorf("http status code: %d", resp.StatusCode))
+// 		return
+// 	}
+
+// 	resp.mock(`{"name":"Alice"}`)
+
+// 	body, err := io.Await[string](resp.Text())
+// 	if err != nil {
+// 		resolve(User{}, err)
+// 		return
+// 	}
+// 	user := User{}
+// 	if err := json.Unmarshal([]byte(body), &user); err != nil {
+// 		resolve(User{}, err)
+// 		return
+// 	}
+
+// 	resolve(user, nil)
+// }
+
+func GetScore() *io.Promise[float64] {
 	panic("todo: GetScore")
-})
+}
 
-var DoUpdate = io.Async[io.Void](func(op string) io.Void {
+func DoUpdate(op string) *io.Promise[io.Void] {
 	panic("todo: DoUpdate")
-})
+}
 
 func main() {
 	user, err := GetUser("123").Await()
@@ -26,15 +111,15 @@ func main() {
 	user, err = io.Race(GetUser("123"), GetUser("456"), GetUser("789")).Await()
 	fmt.Println(user, err)
 
-	user, score, _, err := io.Await3[any, float64, io.Void](GetUser("123"), GetScore(), DoUpdate("update sth."))
+	user, score, _, err := io.Await3[User, float64, io.Void](GetUser("123"), GetScore(), DoUpdate("update sth."))
 	fmt.Println(user, score, err)
 
 	select {
-	case user := <-GetUser("123"):
+	case user := <-GetUser("123").Chan():
 		fmt.Println("user:", user)
-	case score := <-GetScore():
+	case score := <-GetScore().Chan():
 		fmt.Println("score:", score)
-	case <-io.Timeout(5 * time.Second):
+	case <-io.Timeout(5 * time.Second).Chan():
 		fmt.Println("timeout")
 	}
 }

x/io/io.go

@@ -30,10 +30,13 @@ type Void = [0]byte
 
 // -----------------------------------------------------------------------------
 
-type AsyncCall[OutT any] chan OutT
+type AsyncCall[OutT any] interface {
+	Await(timeout ...time.Duration) (ret OutT, err error)
+	Chan() <-chan OutT
+}
 
 // llgo:link AsyncCall.Await llgo.await
-func (AsyncCall[OutT]) Await(timeout ...time.Duration) (ret OutT, err error) {
+func Await[OutT any](call AsyncCall[OutT], timeout ...time.Duration) (ret OutT, err error) {
 	return
 }
 
@@ -61,7 +64,27 @@ func Await3[OutT1, OutT2, OutT3 any](
 
 // -----------------------------------------------------------------------------
 
-type Promise[OutT any] func(...any) AsyncCall[OutT]
+type Promise[OutT any] struct {
+}
+
+func NewPromise[OutT any](fn func(resolve func(OutT, error))) (ret *Promise[OutT]) {
+	ret = &Promise[OutT]{}
+	return
+}
+
+func NewPromiseFromValue[OutT any](value OutT) (ret *Promise[OutT]) {
+	return NewPromise[OutT](func(resolve func(OutT, error)) {
+		resolve(value, nil)
+	})
+}
+
+func (p *Promise[OutT]) Await(timeout ...time.Duration) (ret OutT, err error) {
+	return
+}
+
+func (p *Promise[OutT]) Chan() <-chan OutT {
+	return nil
+}
 
 // llgo:link Async llgo.async
 func Async[OutT any](fn any) (ret Promise[OutT]) {