Split code example into individual match cases; add code for example

blog/content/second-edition/posts/12-async-await/index.md

@@ -387,62 +387,67 @@ TODO
 
 
 ```rust
-impl Future for ExampleStateMachine {
-    type Output = String; // return type of `example`
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
-        loop {
-            match self { // TODO: handle pinning
-                ExampleStateMachine::Start(state) => {
-                    // from body of `example`
-                    let foo_txt_future = async_read_file("foo.txt");
-                    // `.await` operation
-                    let state = WaitingOnFooTxtState {
-                        min_len: state.min_len,
-                        foo_txt_future,
-                    };
-                    *self = ExampleStateMachine::WaitingOnFooTxt(state);
-                }
-                ExampleStateMachine::WaitingOnFooTxt(state) => {
-                    match state.foo_txt_future.poll(cx) {
-                        Poll::Pending => return Poll::Pending,
-                        Poll::Ready(content) => {
-                            // from body of `example`
-                            if content.len() < state.min_len {
-                                let bar_txt_future = async_read_file("bar.txt");
-                                // `.await` operation
-                                let state = WaitingOnBarTxtState {
-                                    content,
-                                    bar_txt_future,
-                                };
-                                *self = ExampleStateMachine::WaitingOnBarTxt(state);
-                            } else {
-                                *self = ExampleStateMachine::End(EndState));
-                                return Poll::Ready(content);
-                            }
-                        }
-                    }
-                }
-                ExampleStateMachine::WaitingOnFooTxt(state) => {
-                    match state.bar_txt_future.poll(cx) {
-                        match state.bar_txt_future.poll(cx) {
-                            Poll::Pending => return Poll::Pending,
-                            Poll::Ready(bar_txt) => {
-                                *self = ExampleStateMachine::End(EndState));
-                                // from body of `example`
-                                return Poll::Ready(state.content + &bar_txt);
-                            }
-                        }
-                    }
-                }
-                ExampleStateMachine::End(_) => {
-                    panic!("poll called after Poll::Ready was returned");
-                }
+ExampleStateMachine::Start(state) => {
+    // from body of `example`
+    let foo_txt_future = async_read_file("foo.txt");
+    // `.await` operation
+    let state = WaitingOnFooTxtState {
+        min_len: state.min_len,
+        foo_txt_future,
+    };
+    *self = ExampleStateMachine::WaitingOnFooTxt(state);
+}
+```
+```rust
+ExampleStateMachine::WaitingOnFooTxt(state) => {
+    match state.foo_txt_future.poll(cx) {
+        Poll::Pending => return Poll::Pending,
+        Poll::Ready(content) => {
+            // from body of `example`
+            if content.len() < state.min_len {
+                let bar_txt_future = async_read_file("bar.txt");
+                // `.await` operation
+                let state = WaitingOnBarTxtState {
+                    content,
+                    bar_txt_future,
+                };
+                *self = ExampleStateMachine::WaitingOnBarTxt(state);
+            } else {
+                *self = ExampleStateMachine::End(EndState));
+                return Poll::Ready(content);
             }
         }
     }
 }
 ```
+```rust
+ExampleStateMachine::WaitingOnFooTxt(state) => {
+    match state.bar_txt_future.poll(cx) {
+        match state.bar_txt_future.poll(cx) {
+            Poll::Pending => return Poll::Pending,
+            Poll::Ready(bar_txt) => {
+                *self = ExampleStateMachine::End(EndState));
+                // from body of `example`
+                return Poll::Ready(state.content + &bar_txt);
+            }
+        }
+    }
+}
+```
+```rust
+ExampleStateMachine::End(_) => {
+    panic!("poll called after Poll::Ready was returned");
+}
+```
+
+
+```rust
+fn example(min_len: usize) -> ExampleStateMachine {
+    ExampleStateMachine::Start(StartState {
+        min_len,
+    })
+}
+```
 
 ### Pinning