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

[Hugo Ferreira <hmf@inescporto.pt>]

Alp Mestan wrote:
> 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 ?
> 

You mean?

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

No. It doens't work.

R,
Hugo F.


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