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Date: Thu, 7 Feb 2013 21:06:19 +0100
From: Gabriel Kerneis <kerneis@pps.jussieu.fr>
To: Jeff Meister <nanaki@gmail.com>
Cc: Ashish Agarwal <agarwal1975@gmail.com>, Caml List <caml-list@inria.fr>
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Subject: Re: [Caml-list] use identity for default function

On Thu, Feb 07, 2013 at 11:53:25AM -0800, Jeff Meister wrote:
> Can't you simply define it this way?
> # external id : 'a -> 'b = "%identity";;
> # let foo ?(f = id) x = f x;;

If using unsafe features is okay, you might do even shorter:

# let foo ?(f = Obj.magic) x = f x ;;
val foo : ?f:('a -> 'b) -> 'a -> 'b = <fun>

But remember that “Obj.magic is not part of the language”!
For some good reason:

# let x : int list = foo 0;;
val x : int list = []

-- 
Gabriel