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Date: Wed, 25 Jun 2008 09:29:48 -0700 (PDT)
From: Dario Teixeira <darioteixeira@yahoo.com>
Subject: Re: [Caml-list] Phantom types: transparency vs rogue unification
To: Jacques Carette <carette@mcmaster.ca>
Cc: caml-list@yquem.inria.fr
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X-Spam: no; 0.00; unification:01 functor:01 dependencies:01 parser:01 sig:01 val:01 sig:01 val:01 parser:01 struct:01 struct:01 cheers:01 1.0:98 2.0:98 1.0:98 

> Note that I would personally implement Stringies_IO a
> Functor over=20
> Stringies rather than having explicit dependencies.
>=20

Hi,

Indeed!  In the meantime I've also thought of a functor-based solution,
which does the job even though it looks rather contrived:

_________________________________________________________
module type PARSER =3D
sig
=09val parse: string -> float
end

module type STRINGIES =3D
sig
=09type 'a t
=09val make: float -> string t
=09val add: string t -> string t -> string t
=09val parse: string -> string t
end

module Stringies (Parser : PARSER): STRINGIES =3D
struct
=09type 'a t =3D float
=09let make x =3D x
=09let add a b =3D a +. b
=09let parse =3D Parser.parse
end

module Myparser : PARSER =3D
struct
=09let parse =3D float_of_string
end

module Mystringies =3D Stringies (Myparser)

open Mystringies

let ola =3D add (make 1.0) (make 2.0);;
let ola =3D add (make 1.0) 2.0;; (* Error *)
_________________________________________________________


Thanks for your time!
Cheers,
Dario Teixeira

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