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Module Lwt_stream

module Lwt_stream: sig .. end
Data streams
type 'a t
A stream holding values of type 'a.

Naming convention: in this module, all functions applying a function to each element of a stream are suffixed by:

This module may undergo redesign or deprecation in the future. See Flaws of Lwt_stream. In the meantime, you may want to consider using alternatives such as lwt-pipe.

Construction


val from : (unit -> 'a option Lwt.t) -> 'a t
from f creates a stream from the given input function. f is called each time more input is needed, and the stream ends when f returns None.

If f, or the thread produced by f, raises an exception, that exception is forwarded to the consumer of the stream (for example, a caller of Lwt_stream.get). Note that this does not end the stream. A subsequent attempt to read from the stream will cause another call to f, which may succeed with a value.

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 preferred that this function be used rather than wrapping f into a function which returns a thread.

The behavior when f raises an exception is the same as for Lwt_stream.from, except that f does not produce a thread.

exception Closed
Exception raised by the push function of a push-stream when pushing an element after the end of stream (= None) has been pushed.
val create : unit -> 'a t * ('a option -> unit)
create () returns a new stream and a push function.

To notify the stream's consumer of errors, either use a separate communication channel, or use a result stream. There is no way to push an exception into a push-stream.

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 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. The elements are pushed into the stream immediately, resulting in a closed stream (in the sense of Lwt_stream.is_closed).
val of_array : 'a array -> 'a t
of_array a creates a stream returning all elements of a. The elements are pushed into the stream immediately, resulting in a closed stream (in the sense of Lwt_stream.is_closed).
val of_string : string -> char t
of_string str creates a stream returning all characters of str. The characters are pushed into the stream immediately, resulting in a closed stream (in the sense of Lwt_stream.is_closed).
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 removes and returns the first element of the stream, if any.
val nget : int -> 'a t -> 'a list Lwt.t
nget n st removes 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 removes and returns the next element of the stream or fails 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 sleeping, or wait for one if none is available.

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

val junk : 'a t -> unit Lwt.t
junk st removes 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 yielding from st.

For example, the read_password function of Lwt_read_line uses it to flush keys 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
Deprecated.Use Lwt_stream.closed.
on_termination st f executes f when the end of the stream st is reached. Note that the stream may still contain elements if Lwt_stream.peek or similar was used.
val on_terminate : 'a t -> (unit -> unit) -> unit
Deprecated.Use Lwt_stream.closed.
Same as Lwt_stream.on_termination.

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 return 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 values, 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_map f s find and map at the same time.
val combine : 'a t -> 'b t -> ('a * 'b) t
combine s1 s2 combines two streams. The stream will end when either 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
val wrap_exn : 'a t -> 'a Lwt.result t
wrap_exn s is a stream s' such that each time s yields a value v, s' yields Result.Ok v, and when the source of s raises an exception e, s' yields Result.Error e.

Note that push-streams (as returned by Lwt_stream.create) never raise exceptions.

If the stream source keeps raising the same exception e each time the stream is read, s' is unbounded. Reading it will produce Result.Error e indefinitely.
Since 2.7.0


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)))


Deprecated


type 'a result =
| Value of 'a
| Error of exn (*
Deprecated.Replaced by Lwt_stream.wrap_exn, which uses Lwt.result.
A value or an error.
*) 
val map_exn : 'a t -> 'a result t
Deprecated.Use Lwt_stream.wrap_exn.
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.

If the stream source keeps raising the same exception e each time the stream is read, the stream produced by map_exn is unbounded. Reading it will produce Lwt_stream.Error e indefinitely.