Re: [Caml-list] Cannot safely evaluate the definition of the recursively-defined module

[Alp Mestan <alp@mestan.fr>]

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Hi,

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

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

should be okay. Shouldn't it ?

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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-- 
Alp Mestan
In charge of the C++ section on Developpez.com.

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