feat(fsharp): m11 pong capstone (model, rules, view, app) with tests

Co-Authored-By: Claude Opus 5.5 <[email protected]>

fsharp/solutions/Pong/App.fs

@@ -0,0 +1,36 @@
+/// m11 pong app: the same wiring as App.fs (streams in, drawings out), reusing the course's modules.
+module Snake.Pong.App
+
+open Snake
+open Snake.IO
+open Snake.Stream
+open Snake.Pong.Model
+open Snake.Pong.Rules
+open Snake.Pong.View
+
+let FRAME_MS_PONG = 30L
+
+let private paddleKey (key: string) : Paddle option =
+    match key with
+    | "ArrowUp" | "w" | "W" -> Some Paddle.Up
+    | "ArrowDown" | "s" | "S" -> Some Paddle.Down
+    | _ -> None
+
+let pongKey (isDown: bool) (key: string) : PongAction option =
+    match paddleKey key with
+    | Some p -> Some(if isDown then PongAction.Press p else PongAction.Release p)
+    | None -> if isDown && (key = "r" || key = "R") then Some PongAction.Restart else None
+
+let pongActions: Stream<PongAction> =
+    Stream.merge
+        (Stream.merge
+            (Stream.interval FRAME_MS_PONG |> Stream.map (fun _ -> PongAction.Frame))
+            (Stream.keyDowns |> Stream.choose (pongKey true)))
+        (Stream.keyUps |> Stream.choose (pongKey false))
+
+let pongStates (seed: uint32) (actions: Stream<PongAction>) : Stream<PongState> =
+    actions |> Stream.scan pongUpdate (initialPong seed) |> Stream.startWith (initialPong seed)
+
+let pongMain () : IO<Stream<IO<unit>>> =
+    IO.randomSeed ()
+    |> IO.map (fun seed -> pongStates seed pongActions |> Stream.map (fun state -> IO.drawScene (pongView state)))