fix: stream can only return one type

src/Std/Internal/Async.lean

@@ -15,5 +15,6 @@ public import Std.Internal.Async.Select
 public import Std.Internal.Async.Process
 public import Std.Internal.Async.System
 public import Std.Internal.Async.Signal
+public import Std.Internal.Async.IO
 
 public section

src/Std/Internal/Async/IO.lean

@@ -0,0 +1,54 @@
+/-
+Copyright (c) 2025 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sofia Rodrigues
+-/
+module
+
+prelude
+public import Std.Internal.Async.Select
+
+public section
+
+namespace Std
+namespace Internal
+namespace Async
+namespace IO
+
+open Std.Internal.IO.Async
+
+/-!
+This module provides buffered asynchronous I/O operations for efficient reading and writing.
+-/
+
+/--
+Interface for asynchronous reading operations.
+-/
+class AsyncRead (α : Type) (β : Type) where
+  read : α → Async β
+
+/--
+Interface for asynchronous writing operations.
+-/
+class AsyncWrite (α : Type) (β : Type) where
+  write : α → β → Async Unit
+
+  writeAll : α → Array β → Async Unit :=
+    fun socket data => data.forM (write socket)
+
+  flush : α → Async Unit :=
+    fun _ => pure ()
+
+/--
+Interface for asynchronous streaming with selector-based iteration.
+-/
+class AsyncStream (α : Type) (β : outParam Type) where
+  next : α → Selector β
+
+  stop : α → IO Unit :=
+    fun _ => pure ()
+
+end IO
+end Async
+end Internal
+end Std

src/Std/Sync/Channel.lean

@@ -10,9 +10,13 @@ public import Init.System.Promise
 public import Init.Data.Queue
 public import Std.Sync.Mutex
 public import Std.Internal.Async.Select
+public import Std.Internal.Async.IO
 
 public section
 
+open Std.Internal.Async.IO
+open Std.Internal.IO.Async
+
 /-!
 This module contains the implementation of `Std.Channel`. `Std.Channel` is a multi-producer
 multi-consumer FIFO channel that offers both bounded and unbounded buffering as well as synchronous
@@ -24,7 +28,6 @@ for cleaner code.
 -/
 
 namespace Std
-
 namespace CloseableChannel
 
 /--
@@ -753,6 +756,17 @@ partial def forAsync (f : α → BaseIO Unit) (ch : CloseableChannel α)
     | none => return .pure ()
     | some v => do f v; ch.forAsync f prio
 
+instance [Inhabited α] : AsyncStream (CloseableChannel α) (Option α) where
+  next channel := channel.recvSelector
+
+instance [Inhabited α] : AsyncRead (CloseableChannel α) (Option α) where
+  read receiver := Internal.IO.Async.Async.ofIOTask receiver.recv
+
+instance [Inhabited α] : AsyncWrite (CloseableChannel α) α where
+  write receiver x := do
+    let task ← receiver.send x
+    Async.ofAsyncTask <| task.map (Except.mapError (IO.userError ∘ toString))
+
 /--
 This function is a no-op and just a convenient way to expose the synchronous API of the channel.
 -/
@@ -804,7 +818,6 @@ instance [MonadLiftT BaseIO m] : ForIn m (Sync α) α where
   forIn ch b f := private ch.forIn f b
 
 end Sync
-
 end CloseableChannel
 
 /--
@@ -893,6 +906,17 @@ partial def forAsync [Inhabited α] (f : α → BaseIO Unit) (ch : Channel α)
     (prio : Task.Priority := .default) : BaseIO (Task Unit) := do
   BaseIO.bindTask (prio := prio) (← ch.recv) fun v => do f v; ch.forAsync f prio
 
+instance [Inhabited α] : AsyncStream (Channel α) α where
+  next channel := channel.recvSelector
+
+instance [Inhabited α] : AsyncRead (Channel α) α where
+  read receiver := Internal.IO.Async.Async.ofIOTask receiver.recv
+
+instance [Inhabited α] : AsyncWrite (Channel α) α where
+  write receiver x := do
+    let task ← receiver.send x
+    Async.ofTask task
+
 @[inherit_doc CloseableChannel.sync, inline]
 def sync (ch : Channel α) : Channel.Sync α := ch