Module Pa_lwt
module Pa_lwt : sig..end
Syntactic sugars for lwt
This extension add the following sugars:
- anonymous bind:
write stdio "Hello, " >> write stdio "world!"
- lwt-binding:
lwt ch = get_char stdin in
code
is the same as bind (get_char stdin) (fun ch -> code)
Moreover it supports parallel binding:
lwt x = do_something1 ()
and y = do_something2 in
code
will let do_something1 () and do_something2 () runs then bind their result 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>
,
try_lwt
<expr>
with
<branches>
,
try_lwt
<expr>
finally
<expr>
and:
try_lwt
<expr>
with
<branches>
finally
<expr>
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 addedd when needed.
The construction try_lwt <expr> just catch regular exception into lwt exception. i.e. it is the same as catch (fun _ -> <expr>) fail.
- exception raising:
raise_lwt <expr>
This allow exception to be traced when the -lwt-debug switch is passed to the syntax extension.
- 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
- iteration over streams:
for_lwt <patt> in <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>