package sel

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Simple event library

The main loop goes like this

type top_event =
  | NotForMe of Component.Event.t
  | Echo of string

let echo : top_event Event.t =
  On.line Unix.stdin (function
    | Ok s -> Echo s
    | Error _ -> Echo "error")
  |> Event.recurring

let handle_event = function
  | NotForMe e ->
      Component.handle_event e |>
      List.map (Event.map (fun x -> NotForMe x))
  | Echo text ->
      Printf.eprintf "echo: %s\n" text;
      []

let rec loop evs =
  let ready, evs = pop evs in
  let new_evs = handle_event ready in
  loop (Todo.add evs new_evs)

let main () =
  loop (Todo.add Todo.empty [echo; ...])
module Event : sig ... end

The type of events and operations (setting priority, cancelling, ...)

module On : sig ... end

Events one can wait for (read data, pull from queues, ...)

val now : 'a -> 'a Event.t

mix a regular computations with blocking events. E.g. to make a fold interruptible one can do something like:

type event =
  | Fold of (int -> int -> int) * int * int list
  | Other

let handle_event = function
  | Other -> ...
  | Fold(_,acc,[]) -> Printf "done: %s\n" acc; []
  | Fold(f,acc,x::xs) -> [now (Fold (f, f acc x, xs))

let main =
  let rec loop todo =
    match pop_opt todo with
    | None -> exit 0
    | Some e ->
        let es = handle_event e in
        loop (Todo.add todo es)
  in
    loop (Todo.add Todo.empty [now (Fold((+),0,[1;2;3])); ...])
module Todo : sig ... end

Set of events being waited for

val pop : 'a Todo.t -> 'a * 'a Todo.t

wait for one event. If more are ready, return the one with higher priority.

  • raises Failure

    when there is nothing left to do

val pop_opt : 'a Todo.t -> 'a option * 'a Todo.t

same as pop but retuning an option

val pop_timeout : stop_after_being_idle_for:float -> 'a Todo.t -> 'a option * 'a Todo.t

same as pop_opt but retuning a None if no event is ready in stop_after_being_idle_for seconds. Precision is about a tenth of a second.

val wait : 'a Todo.t -> 'a list * 'a list * 'a option * 'a Todo.t

waits until some event is ready. The three lists are, respectively system events, synchronization events (see On.queue and On.queues), and other events (see now). All system and synchronization events which are ready are returned, and are sorted according to the priority (higher priority first). A computation is considered only if it has higher priority than any other event which is ready.

This API cannot be mixed with pop, use one or the other.

val wait_timeout : stop_after_being_idle_for:float -> 'a Todo.t -> 'a list * 'a list * 'a option * 'a Todo.t

Same as wait but returns empty lists if no event is ready in stop_after_being_idle_for seconds. Precision is about a tenth of a second.