Re: [Caml-list] Question on functors (again...)

[Leo White <lpw25@cam.ac.uk>]

> Unfortunately, this is not possible since the ELT signature is  actually more complex than just 'sig type t end'.
> To illustrate this, without showing the original code (which, as you  guessed it, has some extra and maybe unrelated
> complexity), i've tried  to reuse your example, by simply changing

You can still add the constraint to the SET type:

  module type SET = sig
    type t
    type elt
    module Elt : ELT with type t = elt
    val choose: t -> elt
    val singleton: elt -> t
    val string_of: t -> string
  end

You should also remove the equivalent constraint from the `Make`
functor:
   
  module Make (E : ELT) : SET with type elt = E.t = struct
    type elt = E.t
    type t = elt list
    module Elt = E
    let choose s = List.hd s
    let singleton e = [e]
    let string_of s = "{" ^ E.string_of (choose s) ^ "}"
  end

Regards,

Leo