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>