Update Lwt tutorial examples to match new tutorial

In particular:

- Change `C.log` to `log_s`. `log` is the emergency non-blocking version
  that discards data if the buffer is full. We should not encourage its
  use in a tutorial. Also, it doesn't demonstrate using Lwt.

- Use `>>=` rather than `>|=` because the tutorial didn't introduce it
  yet.

- Don't use `_` to ignore exceptions in timeout example.

- Moved some functions out of `start` for clarity.

- Remove mvar and stream examples, as they're no longer in the tutorial.

console/unikernel.ml

@@ -6,9 +6,9 @@ module Main (C: V1_LWT.CONSOLE) = struct
     let rec loop = function
       | 0 -> Lwt.return_unit
       | n ->
-        C.log c "hello";
+        C.log_s c "hello" >>= fun () ->
         OS.Time.sleep 1.0 >>= fun () ->
-        C.log c "world";
+        C.log_s c "world" >>= fun () ->
         loop (n-1)
     in
     loop 4

lwt/Makefile

@@ -1,7 +1,7 @@
 include ../Makefile.config
 
 TARGETS=heads1 heads2 heads3 timeout1 timeout2 \
-	echo_server1 echo_server2 int_server stream_server
+	echo_server1 echo_server2
 
 configure: $(patsubst %,%-configure,$(TARGETS))
 build: $(patsubst %,%-build,$(TARGETS))

lwt/src/config.ml

@@ -11,11 +11,6 @@ let (name, main) =
 
       | "echo_server1" -> ("echo_server1", "Unikernels.Echo_server1")
 
-      | "echo_server2" -> ("echo_server2", "Mvar_unikernels.Echo_server2")
-      | "int_server" -> ("int_server", "Mvar_unikernels.Int_server")
-
-      | "stream_server" -> ("stream_server", "Stream_server.Unikernel")
-
   with Not_found -> failwith "Must specify target"
 
 let () =

lwt/src/unikernels.ml

@@ -5,12 +5,10 @@ module Heads1 (C: V1_LWT.CONSOLE) = struct
 
   let start c =
     Lwt.join [
-      (Time.sleep 1.0 >|= fun () ->
-       C.log c "Heads");
-      (Time.sleep 2.0 >|= fun () ->
-       C.log c "Tails");
-    ] >|= fun () ->
-    C.log c ("Finished")
+      (Time.sleep 1.0 >>= fun () -> C.log_s c "Heads");
+      (Time.sleep 2.0 >>= fun () -> C.log_s c "Tails")
+    ] >>= fun () ->
+    C.log_s c ("Finished")
 
 end
 
@@ -43,56 +41,53 @@ end
 
 module Timeout1 (C: V1_LWT.CONSOLE) = struct
 
+  let timeout delay t =
+    Time.sleep delay >>= fun () ->
+    match Lwt.state t with
+    | Lwt.Sleep    -> Lwt.cancel t; Lwt.return None
+    | Lwt.Return v -> Lwt.return (Some v)
+    | Lwt.Fail ex  -> Lwt.fail ex
+
   let start c =
     Random.self_init ();
-
-    let timeout f t =
-      Time.sleep f >>= fun () ->
-      match Lwt.state t with
-      | Lwt.Return v -> Lwt.return (Some v)
-      | _            -> Lwt.cancel t; Lwt.return None
-    in
-
     let t = Time.sleep (Random.float 3.0) >|= fun () -> "Heads" in
-    timeout 2.0 t >>= fun v ->
-    C.log c (match v with None -> "cancelled" | Some v -> v);
-    C.log c "Finished";
-    Lwt.return_unit
+    timeout 2.0 t >>= function
+    | None   -> C.log_s c "Cancelled"
+    | Some v -> C.log_s c (Printf.sprintf "Returned %S" v)
 
 end
 
 module Timeout2 (C: V1_LWT.CONSOLE) = struct
 
+  let timeout delay t =
+    let tmout = Time.sleep delay in
+    Lwt.pick [
+      (tmout >|= fun () -> None);
+      (t >|= fun v -> Some v);
+    ]
+
   let start c  =
     Random.self_init ();
-    let timeout f t =
-      let tmout = Time.sleep f in
-      Lwt.pick [
-        (tmout >|= fun () -> None);
-        (t >|= fun v -> Some v);
-      ]
-    in
     let t = Time.sleep (Random.float 3.0) >|= fun () -> "Heads" in
-    timeout 2.0 t >>= fun v ->
-    C.log c (match v with None -> "Cancelled" | Some v -> v);
-    C.log c "Finished";
-    Lwt.return_unit
+    timeout 2.0 t >>= function
+    | None   -> C.log_s c "Cancelled"
+    | Some v -> C.log_s c (Printf.sprintf "Returned %S" v)
 
 end
 
 module Echo_server1 (C: V1_LWT.CONSOLE) = struct
 
+  let read_line () =
+    OS.Time.sleep (Random.float 2.5) >|= fun () ->
+    String.make (Random.int 20) 'a'
+
   let start c =
-    let read_line () =
-      Time.sleep (Random.float 2.5)
-      >|= fun () ->String.make (Random.int 20) 'a'
-    in
     let rec echo_server = function
       | 0 -> Lwt.return ()
       | n ->
-        read_line () >>= fun s ->
-        C.log c s;
-        echo_server (n-1)
+	read_line () >>= fun s ->
+	C.log_s c s >>= fun () ->
+	echo_server (n - 1)
     in
     echo_server 10