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Date: Tue, 10 Apr 2001 13:32:39 +0200
From: Michel Mauny <Michel.Mauny@inria.fr>
To: reig@dcs.gla.ac.uk
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] variant with tuple arg in pattern match?
Message-ID: <20010410133239.B13189@quincy.inria.fr>
Reply-To: Michel.Mauny@inria.fr
References: <20010410102323.A13306@quincy.inria.fr> <200104101044.LAA10626@crab.dcs.gla.ac.uk>
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In-Reply-To: <200104101044.LAA10626@crab.dcs.gla.ac.uk>; from reig@dcs.gla.ac.uk on Tue, Apr 10, 2001 at 11:44:02AM +0100
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reig@dcs.gla.ac.uk wrote/écrivait (Apr 10 2001, 11:44AM +0100):

> This is how you do it in haskell:
> 
> data T a = I Int
> 	 | B Bool
> 	 | N (T a) (T a) 
> 	 | Uncurried (Int,Int)

Sure. With CamlP4's revised syntax, you would write this as

   type t 'a =
     I of int
   | B of bool
   | N of (t 'a) and (t 'a)      (* parens probably unnecessary *)
   | Uncurried of int * int

> Moreover, the last part (-> 'a t) is the same for all constructors and
> can be omitted like you do in haskell (so that Xavier is happier :)
> 
>    type 'a t =
>      Int : int
>    | Bool : bool
>    | Node : 'a t -> 'a t
>    | Uncurried : int * int

I'm afraid the Node case is ambiguous, here.

Is the type of Node   'a t -> 'a t  -> 'a t
or is it             ('a t -> 'a t) -> 'a t ?

In other words, you can't know wether Node carries functions, or is
curried.

-- Michel
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