lwt

Promises and event-driven I/O
Library lwt.unix
Module Lwt_fmt

This module bridges the gap between Stdlib.Format and Lwt. Although it is not required, it is recommended to use this module with the Fmt library.

Compared to regular formatting function, the main difference is that printing statements will now return promises instead of blocking.

val printf : ( 'a, Format.formatter, unit, unit Lwt.t ) format4 -> 'a

Returns a promise that prints on the standard output. Similar to Stdlib.Format.printf.

val eprintf : ( 'a, Format.formatter, unit, unit Lwt.t ) format4 -> 'a

Returns a promise that prints on the standard error. Similar to Stdlib.Format.eprintf.

Formatters

type formatter

Lwt enabled formatters

type order =
| String of string * int * int(*

String (s, off, len) indicate the output of s at offset off and length len.

*)
| Flush(*

Flush operation

*)
val make_stream : unit -> order Lwt_stream.t * formatter

make_stream () returns a formatter and a stream of all the writing order given on that stream.

val of_channel : Lwt_io.output_channel -> formatter

of_channel oc creates a formatter that writes to the channel oc.

val stdout : formatter

Formatter printing on Lwt_io.stdout.

val stderr : formatter

Formatter printing on Lwt_io.stdout.

val make_formatter : commit:( unit -> unit Lwt.t ) -> fmt:Format.formatter -> unit -> formatter

make_formatter ~commit ~fmt creates a new lwt formatter based on the Stdlib.Format.formatter fmt. The commit function will be called by the printing functions to update the underlying channel.

val get_formatter : formatter -> Format.formatter

get_formatter fmt returns the underlying Stdlib.Format.formatter. To access the underlying formatter during printing, it is recommended to use %t and %a.

Printing

val fprintf : formatter -> ( 'a, Format.formatter, unit, unit Lwt.t ) format4 -> 'a
val kfprintf : ( formatter -> unit Lwt.t -> 'a ) -> formatter -> ( 'b, Format.formatter, unit, 'a ) format4 -> 'b
val ifprintf : formatter -> ( 'a, Format.formatter, unit, unit Lwt.t ) format4 -> 'a
val ikfprintf : ( formatter -> unit Lwt.t -> 'a ) -> formatter -> ( 'b, Format.formatter, unit, 'a ) format4 -> 'b
val flush : formatter -> unit Lwt.t

flush fmt flushes the formatter (as with Stdlib.Format.pp_print_flush) and executes all the printing action on the underlying channel.

Low level functions

val write_order : Lwt_io.output_channel -> order -> unit Lwt.t

write_order oc o applies the order o on the channel oc.

val write_pending : formatter -> unit Lwt.t

Write all the pending orders of a formatter. Warning: This function flush neither the internal format queues nor the underlying channel and is intended for low level use only. You should probably use flush instead.