On Wed, Mar 18, 2009 at 1:08 PM, Hugo Ferreira <hmf@inescporto.pt> wrote:

Hello,

I hope this is not a beginners questions.
I am trying to reuse code via functors,
however I am getting the following error:

Cannot safely evaluate the definition of the recursively-defined module
(refers to "AA.empty" when implemented as a constant value)

I circumvented the problem by not using a
constant value but a function instead. As I
understand it this may cause run-time errors.
My question is: is their any way to make the
following example work.

Specifically, for the example below is their
any way of indicating to the compiler that
AA.q = ASet.t ?

TIA,
Hugo F.

module type AA =
sig
type q
type t = string

val compare: t -> t -> int
val add: t -> q -> q
val empty: unit -> q
end

module rec A1 : AA
= struct
type q = ASet.t
type t = string

let compare s1 s2 = Pervasives.compare s1 s2
let add e s = ASet.add e s
let empty _ = ASet.empty
end
and ASet : Set.S with type elt = A1.t
= Set.Make(A1)

module type Wrap_A =
sig
type t
type q

val init: q
val add: t -> q -> q
end

module Make_A (An_A : AA) : Wrap_A
=
struct
type t = An_A.t
type q = An_A.q

(*let init = ASet.empty*)
let init = An_A.empty ()
let add t q = An_A.add t q
end

module Wrap_A1 = Make_A( A1 )

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