[Caml-list] a push style event combinator

[Satoshi Ogasawara <ogasawara@itpl.co.jp>]

Hello,

I'd like to announce the release of PEC, a push style event combinator.

  PEC : https://github.com/osiire/Pec

This small module(about 350 LOC) provides

- a composable event.
- map, choose, never, join and several useful functions.
- immediate reactions corresponds sending data to events.
- no memory leaks.

I think PEC is useful to write event driven systems. The signature is as follows.

type 'a event

(** [make ()] makes a new event and sender function.*)
val make : unit -> 'a event * ('a -> unit)
val map : ('a -> 'b) -> 'a event -> 'b event

(** [choose l] is a event which will be raised when one of specified events occurred. *)
val choose : 'a event list -> 'a event
val never : 'a event
(** [join ee] is a event which will be raised when a inner event occurred.
    "Inner event" is a event comes from outer event [ee]. *)
val join : 'a event event -> 'a event
(** [bind e f] is [join (map f e)] *)
val bind : 'a event -> ('a -> 'b event) -> 'b event
val scan : ('a -> 'b -> 'a) -> 'a -> 'b event -> 'a event
val filter : ('a -> bool) -> 'a event -> 'a event
val filter_map : ('a -> 'b option) -> 'a event -> 'b event
val zip : 'a event -> 'b event -> ('a * 'b) event
val take_while : ('a -> bool) -> 'a event -> 'a event
val take_while_in : ('a -> bool) -> 'a event -> 'a event
val take_n : int -> 'a event -> 'a event
val once : 'a event -> 'a event
val drop_while : ('a -> bool) -> 'a event -> 'a event
val drop_n : int -> 'a event -> 'a event
val delay : int -> 'a event -> 'a event
val pairwise : 'a event -> ('a * 'a) event

(** [subscribe f e] attaches the [f] to the specified event.
    The [f] will be called when the [e] will occurred. *)
val subscribe : ('a -> unit) -> 'a event -> unit

(** [value e] returns a reference cell which store a latest value *)
val value : 'a -> 'a event -> 'a ref

(** [run ()] runs PEC event system and returns a number of queuing size of sended data. *)
val run : unit -> int


e.g.
 Using PEC, you can write a drag event from mouse events like this.

let (+>) f g = g f
(* E is PEC module *)
let dragging mouse_down mouse_up mouse_move =
  E.bind mouse_down (fun dloc -> E.choose [
    E.map (fun uloc -> `Drop (dloc, uloc)) mouse_up;
    E.map (fun mloc -> `Drag (dloc, mloc)) mouse_move;
  ]
  +> E.take_while_in (function `Drop _ -> false | _ -> true))


Regards,
 ogasawara