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Message-ID: <CAAoLEWsY8oJZGMEy5CXxQT3FA8iTnO_Ct2SSgbqaJ4CW4fjSuA@mail.gmail.com>
From: Jun Furuse <jun.furuse@gmail.com>
To: caml-list <caml-list@inria.fr>
Content-Type: text/plain; charset=ISO-8859-1
Subject: [Caml-list] [ANN] ppx_overload : ppx for user definable SML style
 overloading

Hi,

I have OPAM-released ppx_overload, a ppx for user definable SML style
overloading.

For example you can overload (+) and (+.) to Plus.(+) as follows:

module Plus = struct
  external (+) : 'a -> 'a -> 'a = "%OVERLOADED"
  module Int = struct
    let (+) = Pervasives.(+)
  end
  module Float = struct
    let (+) = Pervasives.(+.)
  end
end

Then Plus.(+) works for int and float additions!

It works as follows:

* Declaration of overloaded values by external "%OVERLOADED"
* List the instances with the same name in its sub modules.
* The uses of overloaded values are resolved to one of their instances
at typing phase.

The overloading of ppx_overload is pretty limited: you cannot derive
overloading by using overloaded values polymorphicially. You cannot
define overloaded double with the overloaded Plus.(+). But still it is
a very interesting ppx example to combine with the OCaml typing.

ppx_overload is now available in OPAM. More detailed explanation how
it works is explained in the project page:
https://bitbucket.org/camlspotter/compiler-libs-hack . Enjoy!

Thanks
Jun