It's Great! Thanks!
On 2012/11/09, at 23:25, Didier Cassirame <didier.cassirame@gmail.com> wrote:
> Dear caml-list,
>
> I have been trying recently to combine classes, modules and variants
> in the following fashion:
>
> module A1 = struct
>
> class ['a] t = object
> constraint 'a = [>`a]
> method m : 'a -> string = function `a -> "a" | `a1 -> "a1" | _ -> "_"
> end
>
> end;;
>
> […]
>
> module type A = sigActually the parameterization would not help here, since you want to put them all in the same list.
>
> class ['a] t : object
> constraint 'a = [>`a]
> method m : 'a -> string
> end
>
> end;;
>
> type m = (module A);;
>
> let l: m list = [ (module A1); (module A2); (module A3)];;
>
> --------------------------------
>
> Unfortunately the list typecheck fails. However, making a list of
> class instances from A1.t, A2.t, A3.t succeed, with the type:
>
> [> `a | `a1 | `a2 | `a3 ] ct list
>
> ct being defined as equal to A.t.
>
> I thought that perhaps I should parameterize the type m from the type
> parameter 'a of A.t to solve my problem, but I am not sure of the
> syntax, or if it's the problem. Does anyone have an idea?
The idea of using first-class modules is to be explicit about types, so using an explicit type definition for a solves the problem.
Jacques Garrigue
module A1 = struct
type a = private [> `a | `a1]
class t = object
method m : a -> string = function `a -> "a" | `a1 -> "a1" | _ -> "_"type a = private [> `a | `a2]
end
end;;
module A2 = struct
class t = object
method m : a -> string = function `a -> "a" | `a2 -> "a2" | _ -> "_"type a = private [> `a | `a3]
end
end;;
module A3 = struct
class t = object
method m : a -> string = function `a -> "a" | `a3 -> "a3" | _ -> "_"type a = private [> `a]
end
end;;
module type A = sig
class t : object
method m : a -> string
end
end;;
type m = (module A);;
let l: m list = [ (module A1); (module A2); (module A3)];;