lwt 2.6.0 · OCaml Package

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 from but with a function that does not return a thread. It is better than wrapping f into a function which returns 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 a reference to be set to an external source. This prevents 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 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 retrieval

exception Empty

Exception raised when trying to retrieve 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 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 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 whether the given stream is empty.

val is_closed : 'a t -> bool

is_closed st returns whether the given stream has been closed. A closed stream is not necessarily empty. It may still contain unread elements. If is_closed s = true, then all subsequent reads until the end of the stream are guaranteed not to block.

since 2.6.0

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

closed st returns a thread that will sleep until the stream has been closed.

since 2.6.0

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

on_termination st f executes f when the end of the stream st is reached. Note that the stream may still contain elements if peek or similar was used.

deprecated
Use closed.

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

Same as on_termination.

deprecated
Use closed.

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 from).

Note that for push-streams (as returned by 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)))