[Caml-list] Terser ppx syntax for common usage (like monads)

["Petter A. Urkedal" <paurkedal@gmail.com>]

Now that we're replacing camlp4 with ppx, we're also replacing e.g.

  lwt x = ....

the longer

  let%lwt x = ...

Now, that's not necessarily a bad thing, but the monad bind operation
tends to be quite invasive, so I'd like to suggest adding a shorter
syntax which the user could choose to map to their most pervasive ppx
rewriter.  I think a good candidate would be

  let* x = ...
  for* x = ... do ... done
  try* ...
  etc.

One way to implement this would be to map kw* to kw%ast, and leave it
to the ppx extensions to accept an option telling it whether to
process "ast" tagged nodes or not. Alternatively, it could be a
compiler option.

My reason for choosing "*" is 1) it looks okay in my opinion, 2) it is
only used as a binary operator, so it can't interfere with existing
code, like e.g. "let!" could.