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From: "Jon Harrop" <jon@ffconsultancy.com>
To: "'Andrew'" <newsgroups.fr@gmail.com>, <caml-list@inria.fr>
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Date: Fri, 29 Apr 2011 13:15:38 +0100
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Subject: RE: [Caml-list] Comparing variant types

Andrew wrote:
> Why not write directly
> 	let dir_equal = fun d1 d2 ->
> 	  | Left Left
> 	  | Right Right
> 	  | Up Up
> 	  | Down Down
> 	  | No_op No_op ->  true
> 	  | _ -> false

You want to fill out your _ pattern with explicit type constructors
otherwise it is fragile wrt new constructors being added to the type.

Cheers,
Jon.