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[Caml-list] multiple includes in module types with shared types
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Date: -- (:)
From: David Monniaux <David.Monniaux@e...>
Subject: [Caml-list] multiple includes in module types with shared types
Hi,

It seems quite logical to have constructs such as:

module type ORDERED_TYPE =
sig
  type t
  val compare: t->t->int
end

module type PRINTABLE_TYPE =
sig
  type t
  val print: Format.formatter->t->unit
end

Now we want to define such things as
module type ORDERED_PRINTABLE_TYPE =
sig
  include ORDERED_TYPE
  include PRINTABLE_TYPE
end
but this is refused since it defines "t" twice.

module type ORDERED_PRINTABLE_TYPE = sig
  include ORDERED_TYPE
  include PRINTABLE_TYPE with type t = t
end
is also refused.

Is there a workaround, short of manually including one of the modules
without the type t?

Alain Frisch suggested
module type ORDERED_TYPE = sig type t val compare: t->t->int end;;
module type PRINTABLE_TYPE =
 sig type s val print: Format.formatter->s->unit end;;

module type ORDERED_PRINTABLE_TYPE = sig
  include ORDERED_TYPE
  include PRINTABLE_TYPE with type s = t
end

but this is very inelegant and has issues of its own.


David Monniaux            http://www.di.ens.fr/~monniaux
Laboratoire d'informatique de l'École Normale Supérieure,
Paris, France






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