feat(fsharp): Fable browser platform, snake and pong pages, build-web.sh

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

fsharp/web/BrowserPlatform.fs

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+/// Browser glue: turns a canvas into a Platform. Impure by nature; not part of the exercises' logic.
+/// `?` (Fable.Core.JsInterop dynamic access) calls browser APIs by name, without type bindings or extra packages.
+module Snake.Web.BrowserPlatform
+
+open Fable.Core
+open Fable.Core.JsInterop
+open Snake.Runtime
+
+[<Global>]
+let private window: obj = jsNative
+
+[<Global>]
+let private crypto: obj = jsNative
+
+// Keys that scroll the page should only steer the game.
+let private prevent = [ "ArrowUp"; "ArrowDown"; "ArrowLeft"; "ArrowRight"; " " ]
+
+let private listen (kind: string) (cb: string -> unit) : unit =
+    window?addEventListener (kind,
+                             fun (e: obj) ->
+                                 let key: string = e?key
+
+                                 if List.contains key prevent then
+                                     e?preventDefault ()
+
+                                 cb key)
+
+// t is the number of milliseconds since the first animation frame.
+let private startClock (onTime: int64 -> unit) : unit =
+    let rec frame (start: float option) : float -> unit =
+        fun now ->
+            let t0 = defaultArg start now
+            onTime (int64 (now - t0))
+            window?requestAnimationFrame (frame (Some t0))
+
+    window?requestAnimationFrame (frame None)
+
+// Fable compiles a uint32 array to a Uint32Array, which is what crypto.getRandomValues fills.
+let private randomSeed () : uint32 =
+    let buf: uint32[] = Array.zeroCreate 1
+    crypto?getRandomValues (buf)
+    buf[0]
+
+/// A Platform drawing on `canvas` (an HTML canvas element) and listening to the window's keys and frames.
+let create (canvas: obj) : Platform =
+    let ctx = canvas?getContext ("2d")
+
+    { FillRect =
+        fun x y w h color ->
+            ctx?fillStyle <- color
+            ctx?fillRect (x, y, w, h)
+      FillText =
+        fun x y text color size align ->
+            ctx?fillStyle <- color
+            ctx?font <- $"{size}px monospace"
+            ctx?textAlign <- align
+            ctx?fillText (text, x, y)
+      RandomSeed = randomSeed
+      StartClock = startClock
+      OnKeyDown = listen "keydown"
+      OnKeyUp = listen "keyup" }
+
+/// The page's `<canvas id="game">`.
+let gameCanvas () : obj = window?document?getElementById ("game")

fsharp/web/PongMain.fs

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+/// fsharp/pong.html loads this module (web/dist/PongMain.js): one call runs Pong (m11).
+module Snake.Web.PongMain
+
+open Snake
+
+Runtime.runApp (BrowserPlatform.create (BrowserPlatform.gameCanvas ())) (Pong.App.pongMain ())

fsharp/web/SnakeMain.fs

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+/// fsharp/index.html loads this module (web/dist/SnakeMain.js): one call runs the whole Snake program.
+module Snake.Web.SnakeMain
+
+open Snake
+
+Runtime.runApp (BrowserPlatform.create (BrowserPlatform.gameCanvas ())) (App.main ())

fsharp/web/Web.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <!-- Fable project for the browser pages: compiles ../src (the student's code) plus the browser glue to JavaScript.
+       Build with ../build-web.sh; it is never part of the .NET test build. -->
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <!-- FS0046: `pure` is reserved for future use by F#; the course keeps the name used by every track. -->
+    <NoWarn>$(NoWarn);FS0046</NoWarn>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="../src/Util.fs" />
+    <Compile Include="../src/Model.fs" />
+    <Compile Include="../src/Rules.fs" />
+    <Compile Include="../src/Random.fs" />
+    <Compile Include="../src/Spawn.fs" />
+    <Compile Include="../src/Game.fs" />
+    <Compile Include="../src/View.fs" />
+    <Compile Include="../src/IO.fs" />
+    <Compile Include="../src/Stream.fs" />
+    <Compile Include="../src/Input.fs" />
+    <Compile Include="../src/App.fs" />
+    <Compile Include="../src/Runtime.fs" />
+    <Compile Include="../src/Pong/Model.fs" />
+    <Compile Include="../src/Pong/Rules.fs" />
+    <Compile Include="../src/Pong/View.fs" />
+    <Compile Include="../src/Pong/App.fs" />
+    <Compile Include="BrowserPlatform.fs" />
+    <Compile Include="SnakeMain.fs" />
+    <Compile Include="PongMain.fs" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Fable.Core" Version="5.6.0" />
+  </ItemGroup>
+</Project>