[Caml-list] Default value in module

["Paul A. Steckler" <steck@stecksoft.com>]

I found myself wanting to define several modules that implement a
module type, where all the implementations but one use the same value
of an item in the type. Essentially, I wanted a default value in the
module type, which I can override if needed. Maybe there's a way to do
this already.

If not, the type could look like:
--
module type Foo =
sig
  val ?x : int = 42
 end
--

and instances could be:

--
module Bar1 : Foo =
struct
  let x = 17
end

module Bar2 : Foo =
struct
end
--

Is this a reasonable idea?

More precisely, I wanted to take an existing module type, add an item
to it, and then edit just the instance with the non-default value. As
it was, I had to edit all the instances. I could have used the class
system to do something similar, but that would have required changing
even more code.

-- Paul