Add Rust example to prior art

Using the no-op `Waker`, we can express generators and coroutines in
Rust.  Let's close our list of prior art examples with that.

Author: traviscross

text/3513-gen-blocks.md

@@ -582,6 +582,31 @@ Note that there is no library being used here and that `yield` is not a keyword
 
 [koka]: https://koka-lang.github.io/
 
+## Rust
+
+In Rust, `async` blocks are built on top of the coroutine transformation.  Using a no-op `Waker`, it's possible to expose this transformation.  With that, we can build generators.  Without the assistance of macros, the result looks like this:
+
+```rust
+let odd_dup = |xs| {
+    Gen::new(async move |mut y| {
+        for x in xs {
+            if x % 2 == 1 {
+                y.r#yield(x * 2).await;
+            }
+        }
+    })
+};
+
+let odd_dup = pin!(odd_dup(1u8..20));
+let odd_dup = odd_dup.init();
+
+for (i, x) in odd_dup.enumerate() {
+    assert_eq!((i as u8 * 2 + 1) * 2, x);
+}
+```
+
+Crates such as [`genawaiter`][] use this technique.
+
 # Unresolved questions
 [unresolved-questions]: #unresolved-questions