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From: Goswin von Brederlow <goswin-v-b@web.de>
To: Yitzhak Mandelbaum <yitzhakm@cs.princeton.edu>
Cc: OCaml mailing list <caml-list@inria.fr>
References: <F3D7441E-ABE9-46D5-ABA5-FC47D3EA7E0E@cs.princeton.edu>
Date: Thu, 10 May 2012 20:44:05 +0200
In-Reply-To: <F3D7441E-ABE9-46D5-ABA5-FC47D3EA7E0E@cs.princeton.edu> (Yitzhak
	Mandelbaum's message of "Thu, 10 May 2012 08:22:51 -0400")
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Subject: Re: [Caml-list] optional functions in modules

Yitzhak Mandelbaum <yitzhakm@cs.princeton.edu> writes:

> Hi,
>
> Is there any "common wisdom" regarding the inclusion of optional functions in a module signature?  The two most obvious approaches involve 1) a pair of boolean flag and a function, where the function raises an exception if unimplemented OR 2) using the option type. I see pros/cons to each approach, but am curious if there's any (unofficial) standard approach.
>
> Yitzhak
> -----------------------------
> Yitzhak Mandelbaum

The extunix module has a trifold solution for this:

* First there is the ExtUnix.All module that has all functions in
  it. Functions that are not available raise Not_available with function
  name as an argument.

* Second there is ExtUnix.All.have : string -> bool option

  (** [have name]
    @return indication whether function [name] is available
    - [Some true] if available
    - [Some false] if not available
    - [None] if not known

    e.g. [have "eventfd"]
  *)

* Third there is ExtUnix.Specific containing only functions available on
  this platform.

MfG
        Goswin