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From: =?ISO-8859-1?Q?J=E9r=E9mie?= Dimino <jeremie@dimino.org>
To: "caml-list@inria.fr" <caml-list@inria.fr>
Date: Wed, 07 Dec 2011 16:28:27 +0100
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Subject: [Caml-list] Generic printer patch

Hi,

I have made a patch for ocaml 3.12.1 which allow to have a generic
printing function. The patch is available here:

  http://www.dimino.org/ocaml-3.12.1-generic-print.patch

Here is how to use it:

  external show : 'a -> string = "%show"

  let () = print_endline (show ([1; 2; 3], Some "foo"))

this will print:

  ([1; 2; 3], Some "foo")

It is also possible to define custom printers, for example:

  module StringMap : sig
    include Map.S with type key = string
    val string_of_t : ('a -> string) -> 'a t -> string
  end = struct
    include Map.Make(String)
    let string_of_t (type a) string_of_a (m : a t) =
      show (bindings m)
  end

  let () = print_endline (show (StringMap.singleton "x" 1))

will print:

  [("x", 1)]

Of course it is limited to what the compiler knows, for example the
following function will always returns "[<poly>; <poly>]":

  let f x = show [x; x]

But i think it is already very useful for debugging.

The git repo is here:

  http://www.dimino.org/gitweb/?p=ocaml-3.12.1-print.git;a=summary

Cheers,

-- 
Jérémie