Module Pa_lwt

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.

• 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