feat: implement handle_cast and handle_continue (#88)

* Implement handling of continue-style requests
* Add handle_cast

riot/lib/gen_server.ml

@@ -1,19 +1,33 @@
 open Global
 
 type 'res req = ..
+type cast_req = ..
+type cont_req = ..
 
 type Message.t +=
   | Call : Pid.t * 'res Ref.t * 'res req -> Message.t
+  | Cast : cast_req -> Message.t
   | Reply : 'res Ref.t * 'res -> Message.t
 
 type 'state init_result = Ok of 'state | Error | Ignore
 
+type ('res, 'state) call_result =
+  | Reply of ('res * 'state)
+  | Reply_continue of ('res * 'state * cont_req)
+
+type 'state cast_result = No_reply of 'state
+
 module type Impl = sig
   type args
   type state
 
   val init : args -> state init_result
-  val handle_call : 'res. 'res req -> Pid.t -> state -> 'res * state
+
+  val handle_call :
+    'res. 'res req -> Pid.t -> state -> ('res, state) call_result
+
+  val handle_cast : cast_req -> state -> state cast_result
+  val handle_continue : cont_req -> state -> state
   val handle_info : Message.t -> state -> unit
 end
 
@@ -35,14 +49,23 @@ let call : type res. Pid.t -> res req -> res =
   in
   receive ~selector ()
 
+let cast pid req = send pid (Cast req)
+
 let rec loop : type args state. (args, state) impl -> state -> unit =
  fun impl state ->
   let (module I : Impl with type args = args and type state = state) = impl in
   match receive_any () with
-  | Call (pid, ref, req) ->
-      let res, state = I.handle_call req pid state in
-      send pid (Reply (ref, res));
-      loop impl state
+  | Call (pid, ref, req) -> (
+      match I.handle_call req pid state with
+      | Reply (res, state) ->
+          send pid (Reply (ref, res));
+          loop impl state
+      | Reply_continue (res, state, cont_req) ->
+          send pid (Reply (ref, res));
+          let state = I.handle_continue cont_req state in
+          loop impl state)
+  | Cast req -> (
+      match I.handle_cast req state with No_reply state -> loop impl state)
   | msg ->
       let _res = I.handle_info msg state in
       loop impl state
@@ -65,5 +88,7 @@ let start_link :
 module Default = struct
   let init _args = Ignore
   let handle_call _req _from _state = failwith "unimplemented"
+  let handle_cast _req _state = failwith "unimplemented"
+  let handle_continue _req _state = failwith "unimplemented"
   let handle_info _msg _state = failwith "unimplemented"
 end

riot/lib/key_value_store.ml

@@ -16,11 +16,15 @@ module MakeServer (B : Base) = struct
   let init () = Gen_server.Ok { tbl = Hashtbl.create 0 }
 
   let handle_call :
-      type res. res Gen_server.req -> Pid.t -> state -> res * state =
+      type res.
+      res Gen_server.req ->
+      Pid.t ->
+      state ->
+      (res, state) Gen_server.call_result =
    fun req _from state ->
     match req with
-    | Get k -> (Hashtbl.find_opt state.tbl k, state)
-    | Put (k, v) -> (Hashtbl.replace state.tbl k v, state)
+    | Get k -> Gen_server.Reply (Hashtbl.find_opt state.tbl k, state)
+    | Put (k, v) -> Gen_server.Reply (Hashtbl.replace state.tbl k v, state)
     | _ -> failwith "invalid call"
 end
 

riot/riot.mli

@@ -352,6 +352,9 @@ module Gen_server : sig
       ]}
     *)
 
+  type cast_req = ..
+  type cont_req = ..
+
   (** [state init_result] is used to initialize a new generic server. *)
   type 'state init_result =
     | Ok of 'state
@@ -360,6 +363,12 @@ module Gen_server : sig
         (** use this value to crash the process and notify a supervisor of it *)
     | Ignore  (** use this value to exit the process normally *)
 
+  type ('res, 'state) call_result =
+    | Reply of ('res * 'state)
+    | Reply_continue of ('res * 'state * cont_req)
+
+  type 'state cast_result = No_reply of 'state
+
   (** [Impl] is the module type of the generic server base implementations. You
       can use this type when defining new gen servers like this:
 
@@ -380,7 +389,12 @@ module Gen_server : sig
     type state
 
     val init : args -> state init_result
-    val handle_call : 'res. 'res req -> Pid.t -> state -> 'res * state
+
+    val handle_call :
+      'res. 'res req -> Pid.t -> state -> ('res, state) call_result
+
+    val handle_cast : cast_req -> state -> state cast_result
+    val handle_continue : cont_req -> state -> state
     val handle_info : Message.t -> state -> unit
   end
 
@@ -396,6 +410,11 @@ module Gen_server : sig
       TODO(leostera): add ?timeout param
     *)
 
+  val cast : Pid.t -> cast_req -> unit
+  (** [cast pid req] will send a type-safe request [req] to the generic server behind [pid]
+      and does not wait for a response.
+    *)
+
   val start_link :
     ('args, 'state) impl -> 'args -> (Pid.t, [> `Exn of exn ]) result
   (** [start_link (module S) args] will spawn and link a new process that will

test/gen-servers/main.ml

@@ -18,10 +18,12 @@ module Twitch = struct
 
   type _ Gen_server.req +=
     | Is_connected : bool Gen_server.req
+    | Status_value : int Gen_server.req
     | Profile :
         profile_req
         -> (user, [ `Twitch_error of error ]) result Gen_server.req
 
+  type Gen_server.cont_req += Update_status : int -> Gen_server.cont_req
   type args = { verbose : bool }
 
   module Server : Gen_server.Impl with type args = args = struct
@@ -31,29 +33,46 @@ module Twitch = struct
     let init _args = Gen_server.Ok { status = 1 }
 
     let handle_call :
-        type res. res Gen_server.req -> Pid.t -> state -> res * state =
+        type res.
+        res Gen_server.req ->
+        Pid.t ->
+        state ->
+        (res, state) Gen_server.call_result =
      fun req _from state ->
       match req with
-      | Is_connected -> (true, state)
+      | Is_connected -> Gen_server.Reply (true, state)
+      | Status_value -> Gen_server.Reply (state.status, state)
       | Profile _ ->
-          ( Ok { name = "Jonathan Archer"; email = "[email protected]" },
-            state )
+          Gen_server.Reply_continue
+            ( Ok { name = "Jonathan Archer"; email = "[email protected]" },
+              state,
+              Update_status 2 )
 
     let handle_info _msg _state = ()
+
+    let handle_continue cont_req _state =
+      match cont_req with Update_status n -> { status = n }
+
+    let handle_cast _cast_req _state = failwith "unimplemented"
   end
 
   let start_link ?(verbose = false) () =
     Gen_server.start_link (module Server) { verbose }
 
   let is_connected pid = Gen_server.call pid Is_connected
   let profile pid ~id = Gen_server.call pid (Profile { id })
+  let status pid = Gen_server.call pid Status_value
 end
 
 let main () =
   let (Ok _) = Logger.start () in
   let (Ok pid) = Twitch.start_link () in
   if Twitch.is_connected pid then Logger.info (fun f -> f "connected to twitch");
+  let status = Twitch.status pid in
+  Logger.info (fun f -> f "Status is %d" status);
   let (Ok user) = Twitch.profile pid ~id:1 in
-  Logger.info (fun f -> f "Welcome, %s!" user.name)
+  Logger.info (fun f -> f "Welcome, %s!" user.name);
+  let status = Twitch.status pid in
+  Logger.info (fun f -> f "Status is %d" status)
 
 let () = Riot.run @@ main