Re: [Caml-list] Generic printer patch

[Alex Rubinsteyn <alex.rubinsteyn@gmail.com>]

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Cool! Thanks for writing this. Can you explain how defining a custom
printer works? The new language features still bewilder me.
On Dec 7, 2011 10:29 AM, "Jérémie Dimino" <jeremie@dimino.org> wrote:

> 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
>
>
>
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