> I'd like to do something that looks like :
>
> module A =
> (struct
> type t = { mutable field : int }
> end : sig
> type t = { field : int }
> end)
The usual idea of a module is to hide the concrete implementation of some
data type and to provide for functions that only allow the kind of access
you want.
So you could write, e.g.:
module A :
sig
type t
val field : t -> int
end =
struct
type t = { mutable field : int }
let field x = x.field
let internal_only x n = x.field <- n
end
As you can see, the signature to which "A" is restricted, does not show how
"t" is implemented (mutable/nonmutable, whatever).
It only provides for a function "field" that allows read-only access to the
field in type t. However, the user of this module would not (and need not)
even know that "t" is implemented as a record with a field of this name.
He would only have to write "field foo", for example, to get the
information needed.
Function "internal_only" destructively updates the record field, but it is
not visible to the outside, because it does not appear in the signature.
Regards,
Markus Mottl
-- Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl
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