Module Lwt_fmt

Format API for Lwt-powered IOs

This module bridges the gap between 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 Format.printf.

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

Returns a promise that prints on the standard error. Similar to 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 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 Format.formatter. To access the underlying formatter during printing, it isvrecommended 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 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.