Module Ppx_lwt
module Ppx_lwt : sig..end
Ppx syntax extension for Lwt
Ppx extensions ¶
This Ppx extension adds various syntactic shortcut for lwt programming. It needs OCaml >= 4.02 and 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))
Due to a bug in the OCaml parser, if you'd like to put a type constraint on the variable, please write
let (foo : int) = do_something in
code
Not using parentheses will confuse the OCaml parser.
- 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>
val mapper : Migrate_parsetree.OCaml_410.Ast.Ast_mapper.mapper