Module Lwt_stream

module Lwt_stream : sig..end

Data streams


type 'a t

Type of a stream holding values of type 'a

Naming convention: in this module all function taking a function which is applied to all element of the streams are suffixed by:

  • _s when the function returns a thread and calls are serialised
  • _p when the function returns a thread and calls are parallelised
Construction
val from : (unit -> 'a option Lwt.t) -> 'a t

from f creates an stream from the given input function. f is called each time more input is needed, and the stream ends when f returns None.

val from_direct : (unit -> 'a option) -> 'a t

from_direct f does the same as Lwt_stream.​from but with a function that does not return a thread. It is better than wrapping f into a function which return a thread.

exception Closed

Exception raised by the push function of a push-stream when pushing an element after the end of stream (= None) have been pushed.

val create : unit -> 'a t * ('a option -> unit)

create () returns a new stream and a push function.

val create_with_reference : 
  unit -> 'a t * ('a option -> unit) * ('b -> unit)

create_with_reference () returns a new stream and a push function. The last function allows to set a reference to an external source. This prevent the external source from being garbage collected.

For example, to convert a reactive event to a stream:

let stream, push, set_ref = Lwt_stream.create_with_reference () in
        set_ref (map_event push event)
exception Full

Exception raised by the push function of a bounded push-stream when the stream queue is full and a thread is already waiting to push an element.

class type ['a]bounded_push = object..end

Type of sources for bounded push-streams.

val create_bounded : int -> 'a t * 'a bounded_push

create_bounded size returns a new stream and a bounded push source. The stream can hold a maximum of size elements. When this limit is reached, pushing a new element will block until one is consumed.

Note that you cannot clone or parse (with Lwt_stream.​parse) a bounded stream. These functions will raise Invalid_argument if you try to do so.

It raises Invalid_argument if size < 0.

val of_list : 'a list -> 'a t

of_list l creates a stream returning all elements of l

val of_array : 'a array -> 'a t

of_array a creates a stream returning all elements of a

val of_string : string -> char t

of_string str creates a stream returning all characters of str

val clone : 'a t -> 'a t

clone st clone the given stream. Operations on each stream will not affect the other.

For example:

# let st1 = Lwt_stream.of_list [1; 2; 3];;
        val st1 : int Lwt_stream.t = <abstr>
        # let st2 = Lwt_stream.clone st1;;
        val st2 : int Lwt_stream.t = <abstr>
        # lwt x = Lwt_stream.next st1;;
        val x : int = 1
        # lwt y = Lwt_stream.next st2;;
        val y : int = 1

It raises Invalid_argument if st is a bounded push-stream.

Destruction
val to_list : 'a t -> 'a list Lwt.t

Returns the list of elements of the given stream

val to_string : char t -> string Lwt.t

Returns the word composed of all characters of the given stream

Data retreival
exception Empty

Exception raised when trying to retreive data from an empty stream.

val peek : 'a t -> 'a option Lwt.t

peek st returns the first element of the stream, if any, without removing it.

val npeek : int -> 'a t -> 'a list Lwt.t

npeek n st returns at most the first n elements of st, without removing them.

val get : 'a t -> 'a option Lwt.t

get st remove and returns the first element of the stream, if any.

val nget : int -> 'a t -> 'a list Lwt.t

nget n st remove and returns at most the first n elements of st.

val get_while : ('a -> bool) -> 'a t -> 'a list Lwt.t
val get_while_s : ('a -> bool Lwt.t) -> 'a t -> 'a list Lwt.t

get_while f st returns the longest prefix of st where all elements satisfy f.

val next : 'a t -> 'a Lwt.t

next st remove and returns the next element of the stream, of fail with Lwt_stream.​Empty if the stream is empty.

val last_new : 'a t -> 'a Lwt.t

last_new st returns the last element that can be obtained without sleepping, or wait for one if no one is already available.

If fails with Lwt_stream.​Empty if the stream has no more elements

val junk : 'a t -> unit Lwt.t

junk st remove the first element of st.

val njunk : int -> 'a t -> unit Lwt.t

njunk n st removes at most the first n elements of the stream.

val junk_while : ('a -> bool) -> 'a t -> unit Lwt.t
val junk_while_s : ('a -> bool Lwt.t) -> 'a t -> unit Lwt.t

junk_while f st removes all elements at the beginning of the streams which satisfy f.

val junk_old : 'a t -> unit Lwt.t

junk_old st removes all elements that are ready to be read without yeilding from st.

For example the read_password function of Lwt_read_line use that to junk key previously typed by the user.

val get_available : 'a t -> 'a list

get_available st returns all available elements of l without blocking

val get_available_up_to : int -> 'a t -> 'a list

get_available_up_to n st returns up to n elements of l without blocking

val is_empty : 'a t -> bool Lwt.t

is_empty st returns wether the given stream is empty

val on_terminate : 'a t -> (unit -> unit) -> unit

on_terminate st f executes f when the end of the stream st is reached. Note that the stream may still contains elements if Lwt_stream.​peek or similar was used.

Stream transversal

Note: all the following functions are destructive.

For example:

# let st1 = Lwt_stream.of_list [1; 2; 3];;
      val st1 : int Lwt_stream.t = <abstr>
      # let st2 = Lwt_stream.map string_of_int st1;;
      val st2 : string Lwt_stream.t = <abstr>
      # lwt x = Lwt_stream.next st1;;
      val x : int = 1
      # lwt y = Lwt_stream.next st2;;
      val y : string = "2"
val choose : 'a t list -> 'a t

choose l creates an stream from a list of streams. The resulting stream will returns elements returned by any stream of l in an unspecified order.

val map : ('a -> 'b) -> 'a t -> 'b t
val map_s : ('a -> 'b Lwt.t) -> 'a t -> 'b t

map f st maps the value returned by st with f

val filter : ('a -> bool) -> 'a t -> 'a t
val filter_s : ('a -> bool Lwt.t) -> 'a t -> 'a t

filter f st keeps only value x such that f x is true

val filter_map : ('a -> 'b option) -> 'a t -> 'b t
val filter_map_s : ('a -> 'b option Lwt.t) -> 'a t -> 'b t

filter_map f st filter and map st at the same time

val map_list : ('a -> 'b list) -> 'a t -> 'b t
val map_list_s : ('a -> 'b list Lwt.t) -> 'a t -> 'b t

map_list f st applies f on each element of st and flattens the lists returned

val fold : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b Lwt.t
val fold_s : ('a -> 'b -> 'b Lwt.t) -> 'a t -> 'b -> 'b Lwt.t

fold f s x fold_like function for streams.

val iter : ('a -> unit) -> 'a t -> unit Lwt.t
val iter_p : ('a -> unit Lwt.t) -> 'a t -> unit Lwt.t
val iter_s : ('a -> unit Lwt.t) -> 'a t -> unit Lwt.t

iter f s iterates over all elements of the stream

val find : ('a -> bool) -> 'a t -> 'a option Lwt.t
val find_s : ('a -> bool Lwt.t) -> 'a t -> 'a option Lwt.t

find f s find an element in a stream.

val find_map : ('a -> 'b option) -> 'a t -> 'b option Lwt.t
val find_map_s : ('a -> 'b option Lwt.t) -> 'a t -> 'b option Lwt.t

find f s find and map at the same time.

val combine : 'a t -> 'b t -> ('a * 'b) t

combine s1 s2 combine two streams. The stream will ends when the first stream ends.

val append : 'a t -> 'a t -> 'a t

append s1 s2 returns a stream which returns all elements of s1, then all elements of s2

val concat : 'a t t -> 'a t

concat st returns the concatenation of all streams of st.

val flatten : 'a list t -> 'a t

flatten st = map_list (fun l -> l) st

type 'a result =  | Value of 'a | Error of exn

A value or an error.

val map_exn : 'a t -> 'a result t

map_exn s returns a stream that captures all exceptions raised by the source of the stream (the function passed to Lwt_stream.​from).

Note that for push-streams (as returned by Lwt_stream.​create) all elements of the mapped streams are values.

Parsing
val parse : 'a t -> ('a t -> 'b Lwt.t) -> 'b Lwt.t

parse st f parses st with f. If f raise an exception, st is restored to its previous state.

It raises Invalid_argument if st is a bounded push-stream.

Misc
val hexdump : char t -> string t

hexdump byte_stream returns a stream which is the same as the output of hexdump -C.

Basically, here is a simple implementation of hexdump -C:

let () = Lwt_main.run (Lwt_io.write_lines Lwt_io.stdout (Lwt_stream.hexdump (Lwt_io.read_lines Lwt_io.stdin)))