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

create () returns a new stream and a push function

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



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.‚ÄčEmpty if the stream is empty.

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

next_new st if no element are available on st without sleeping, then it is the same as next st. Otherwise it removes all elements of st that are ready except the last one, and return it.

If fails with Lwt_stream.‚ÄčEmpty 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 l returns all available elements of l without blocking

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

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

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

is_empty enum returns wether the given stream is empty


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


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.


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:

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