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Date: Wed, 25 Apr 2001 09:16:29 -0700 (PDT)
From: Brian Rogoff <bpr@best.com>
To: Francois Thomasset <Francois.Thomasset@inria.fr>
cc: caml-list@inria.fr
Subject: Re: [Caml-list] le neophyte et les modules, types parametres
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On Wed, 25 Apr 2001, Francois Thomasset wrote:
> D=E9sol=E9 de poser des qustions simplistes mais je suis perdu dans les m=
odules.
> Dans l'id=E9e de construire une table de symboles je d=E9finis ceci :
> # type symbol =3D string * int ;;
> # type comparison =3D Equiv | Smaller | Greater;;
> # module type ORDERED =3D
>     sig
>       type 'a t
>       val order : 'a t -> 'a t -> comparison
>     end;;
> module type ORDERED =3D
>   sig type 'a t val order : 'a t -> 'a t -> comparison end
> # module type AVL_FUNCTOR =3D functor ( Key : ORDERED ) ->
>   sig
>     type 'a key =3D 'a Key.t
>     type avl_btree =3D ('a key * int) btree
>     ...
>   end;;
> The type constructor Key.t expects 1 argument(s),
> but is here applied to 0 argument(s)
>=20
> D'accord je suppose que c'est le type 'a qui manque (un jour ce sera les=
=20
> morceaux d'environnement attach=E9s aux symboles, donc je n'ai pas envie =
de=20
> pr=E9ciser tout de suite) ; mais je ne comprends pas comment le dire autr=
ement=20
> que ci-dessus ; quelque chose a du m'=E9chapper...
>=20
> Question: how to use a parameter type in a module, cf example above

That looks fine, other than the missing type parameter 'a in your
definition of avl_btree. That would give a different error message than
the one you show though, so I don't understand that message either.=20

The following should compile:

type comparison =3D Equiv | Smaller | Greater;;

module type ORDERED =3D
  sig
    type 'a t
    val order : 'a t -> 'a t -> comparison
  end;;

type 'a btree =3D Leaf | Node of 'a * 'a btree * 'a btree;;

module type AVL_FUNCTOR =3D functor ( Key : ORDERED ) ->
  sig
    type 'a key =3D 'a Key.t
    type 'a avl_btree =3D ('a key * int) btree
  end;;

-- Brian


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