feat(fsharp): m07 io and m08 stream with tests

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

fsharp/src/IO.fs

@@ -0,0 +1,56 @@
+/// m07 io: effects as values. An `IO<'a>` is a description of a program that, when interpreted, produces an `'a`:
+///   - `Pure a`          finished, nothing left to do
+///   - `Effect (op, k)`  perform `op`, then continue with `k result` (which returns another IO)
+/// Building an IO never performs anything; only an interpreter (`trace` here, `Runtime.runIO` in m09) does.
+module Snake.IO
+
+open Snake.View
+
+/// An operation an IO program can ask the outside world to perform.
+type Op =
+    | Draw of Shape
+    | RandomSeed
+
+/// What the outside world answers: `Done` for a `Draw`, `Seed value` (an unsigned 32-bit number) for a `RandomSeed`.
+type OpResult =
+    | Done
+    | Seed of uint32
+
+type IO<'a> =
+    | Pure of 'a
+    | Effect of Op * (OpResult -> IO<'a>)
+
+/// The result of `trace`: the final value and the operations performed, in execution order.
+type Traced<'a> = { Result: 'a; Ops: Op list }
+
+/// An IO that does nothing and produces `a`.
+let pure (a: 'a) : IO<'a> = failwith "TODO m07"
+
+/// An IO that performs the single operation `op` and produces its result: `Effect (op, pure)`.
+let effect (op: Op) : IO<OpResult> = failwith "TODO m07"
+
+/// Run `io`, then feed its result to `f` to get the next IO.
+/// `Pure a`: `f a`. `Effect (op, k)`: the same op, with the continuation extended by `f`.
+let bind (f: 'a -> IO<'b>) (io: IO<'a>) : IO<'b> = failwith "TODO m07"
+
+/// Transform the result with `f`. Must not call `f` until the IO is interpreted.
+let map (f: 'a -> 'b) (io: IO<'a>) : IO<'b> = failwith "TODO m07"
+
+/// Run the IOs one after another, left to right, producing `()`. `sequence []` performs nothing.
+let sequence (ios: IO<unit> list) : IO<unit> = failwith "TODO m07"
+
+/// An IO that draws one shape (a `Rect` or `Text` from m06) and produces `()`.
+let draw (shape: Shape) : IO<unit> = failwith "TODO m07"
+
+/// An IO that asks the outside world for a random seed and produces it (the `value` of the `Seed` answer).
+/// It is a function of `unit` (use it as `randomSeed ()`) because F# evaluates module-level values as soon as
+/// the module is used; every call returns the same description.
+let randomSeed () : IO<uint32> = failwith "TODO m07"
+
+/// Draw every shape of a scene in order: `sequence (List.map draw scene)`.
+let drawScene (scene: Scene) : IO<unit> = failwith "TODO m07"
+
+/// A pure interpreter for tests. Answers every `RandomSeed` with `Seed seed` and every `Draw` with `Done`.
+/// Returns the final value and the operations in the order they were executed.
+/// Implemented by recursion, with no mutation.
+let trace (seed: uint32) (io: IO<'a>) : Traced<'a> = failwith "TODO m07"