/usr/lib/ocaml/lwt/ppx_lwt.mli is in liblwt-ocaml-dev 2.7.1-4build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 | (* Lightweight thread library for OCaml
* http://www.ocsigen.org/lwt
* Module Ppx_lwt
* Copyright (C) 2014 Gabriel Radanne, Peter Zotov.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, with linking exceptions;
* either version 2.1 of the License, or (at your option) any later
* version. See COPYING file for details.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
* 02111-1307, USA.
*)
(** Ppx syntax extension for Lwt *)
(** {2 Ppx extensions}
This Ppx extension adds various syntactic shortcut for lwt programming.
It needs OCaml >= 4.02 and {{:https://github.com/alainfrisch/ppx_tools}ppx_tools}.
To use it, simply use the ocamlfind package [lwt.ppx].
This extension adds the following syntax:
- lwt-binding:
{[
let%lwt ch = get_char stdin in
code
]}
is the same as [bind (get_char stdin) (fun ch -> code)].
Moreover, it supports parallel binding:
{[
let%lwt x = do_something1 ()
and y = do_something2 in
code
]}
will run [do_something1 ()] and [do_something2 ()], then
bind their results to [x] and [y]. It is the same as:
{[
let t1 = do_something1
and t2 = do_something2 in
bind t1 (fun x -> bind t2 (fun y -> code))
]}
- exception catching:
{[
try%lwt
<expr>
with
<branches>
]}
For example:
{[
try%lwt
f x
with
| Failure msg ->
prerr_endline msg;
return ()
]}
is expanded to:
{[
catch (fun () -> f x)
(function
| Failure msg ->
prerr_endline msg;
return ()
| exn ->
Lwt.fail exn)
]}
Note that the [exn -> Lwt.fail exn] branch is automatically added
when needed.
- finalizer:
{[
(<expr>) [%finally <expr>]
]}
You can use [[%lwt.finally ...]] instead of [[%finally ...]].
- assertion:
{[
assert%lwt <expr>
]}
- for loop:
{[
for%lwt i = <expr> to <expr> do
<expr>
done
]}
and:
{[
for%lwt i = <expr> downto <expr> do
<expr>
done
]}
- while loop:
{[
while%lwt <expr> do
<expr>
done
]}
- pattern matching:
{[
match%lwt <expr> with
| <patt_1> -> <expr_1>
...
| <patt_n> -> <expr_n>
]}
Exception cases are also supported:
{[
match%lwt <expr> with
| exception <exn> -> <expr_1>
| <patt_2> -> <expr_2>
...
| <patt_n> -> <expr_n>
]}
- conditional:
{[
if%lwt <expr> then
<expr_1>
else
<expr_2>
]}
and
{[
if%lwt <expr> then <expr_1>
]}
- exception raising:
For all other expression, the construct
{[
[%lwt <expr>]
]}
is expanded to:
{[
Lwt.catch (fun () -> <expr>) Lwt.fail
]}
It allows to encode the old [raise_lwt <e>] as [[%lwt raise <e>]], and offers a convenient way to interact with non-Lwt code.
{2 Debug}
By default, the debug mode is enabled. This means that the [backtrace] versions of the [bind], [finalize] and [catch] functions are used, enabling proper backtraces for the Lwt exceptions.
The debug mode can be disabled with the option [-no-debug]:
{v
$ ocamlfind ocamlc -package lwt.ppx \
-ppxopt lwt.ppx,-no-debug -linkpkg -o foo foo.ml
v}
{2 Sequence}
It is also possible to sequence Lwt operations with the [>>] operator:
{[
write stdout "Hello, " >> write stdout "world!"
]}
By default, each operation must return [unit Lwt.t]. This constraint can be
lifted with the option [-no-strict-sequence]. The operator can be disabled
with the option [-no-sequence].
If you are mixing `>>` and `;`, you need to use parentheses or `begin`/`end`
to get the result you expect:
{[
write stdout "Hello, " >> (ignore (); write stdout "world!")
]}
Note that unlike [>>=], [>>] is not an OCaml value. it is a piece of syntax
added by the ppx rewriter - i.e., you cannot refer to [(>>)].
{2 Logging}
The logging syntax extension is enabled with [-log].
It will replace expressions of the form:
{[
Lwt_log.info_f ~section "x = %d" x
]}
by
{[
if Lwt_log.Section.level section <= Lwt_log.Info then
Lwt_log.info_f ~section "x = %d" x
else
return ()
]}
Notes:
- The application must be complete. For example: [Log.info "%d"]
will make compilation fail.
- Debug messages are removed if the option [-no-debug] is passed.
*)
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