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In-Reply-To: <551BE19E.3010302@digirati.com.br>
References: <551AE480.1000008@digirati.com.br>
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Date: Wed, 1 Apr 2015 13:27:36 +0100
Message-ID: <CAAxsn=F1Q9d=SLoH=p2n6u8pSmmfTdrnU_Z9Y7kA71Wfgj89Ww@mail.gmail.com>
From: Jeremy Yallop <yallop@gmail.com>
To: Andre Nathan <andre@digirati.com.br>
Cc: caml users <caml-list@inria.fr>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [Caml-list] GADTs and Menhir

On 1 April 2015 at 13:16, Andre Nathan <andre@digirati.com.br> wrote:
> I'm happy that it works, but the `any` type is a bit of a mistery to me.
> In Jeremy's email it's explained as
>
> "An existential to hide the type index of a well-typed AST, making it
> possible to write functions that return constructed ASTs whose type is
> not statically known."
>
> Does anyone have a reference to literature that explains this technique
> (I'm guessing that would be Pierce's book)? The OCaml manual briefly
> shows an example with a `dyn` type, but not much is said about it.

There's a more detailed explanation of the technique in the lecture
notes on the following page:

   http://www.cl.cam.ac.uk/teaching/1415/L28/materials.html

The section you want is

    8.4.2 Pattern: building GADT values

on p83 of the notes from 9 February, but it might also be helpful to
look through some of the earlier notes for background.

Jeremy.