Use Lwt_ppx in a dune project

Lwt_ppx offers a syntax for Lwt that is the equivalent to async/await for JavaScript syntax.

The documentation is good but it doesn’t describes how to use this syntax in a dune project.

• https://ocsigen.org/lwt/5.2.0/api/Ppx_lwt

In your dune file just add the following line:

(preprocess (pps lwt_ppx))

This line tells dune to preprocess the code code with an AST rewriter that knows how to transform Lwt promises written like this:

let%lwt ch = get_char string in
code ...

For example:

(library
  (name        mylib)
  (public_name mylib)
  (libraries lwt cohttp cohttp-lwt cohttp-lwt-unix yojson lwt_ppx)
  (preprocess (pps lwt_ppx))
)