Re: Recursive Variants of Set

As the variant constructors Common and ObjStore are declared in the
Identity sub-module, you should access them as Identity.Common and
Identity.ObjStore:

# IdSet.elements
  (List.fold_right IdSet.add
     [Identity.Common "C"; Identity.ObjStore "OS"]
     IdSet.empty);;
- : IdSet.elt list = [Identity.Common "C"; Identity.ObjStore "OS"]

It is also possible to "open" the Identity module to put its names in scope
so that you don't have to prefix them. You can also (in recent-ish versions
of OCaml) open a module locally using the syntaxes (let open <module> in
<expression>) or (<module>.(<expression>)), for example:

IdSet.elements
  (List.fold_right IdSet.add
     Identity.([Common "C"; ObjStore "OS"])
     IdSet.empty);;



On Mon, Jul 14, 2014 at 4:51 PM, Jacques du Preez [email protected]
[ocaml_beginners] <[email protected]> wrote:

>
>
> Hi,
>
> Okay, so I got the recursive module right, and a variant that's a set of
> the variant type itself - Id of IdSet.t:
>
> module rec Identity :
> sig
>   type id = | Id of IdSet.t
>     | Common of string
>     | ObjStore of string
> end
> = struct
>   type id = | Id of IdSet.t
>     | Common of string
>     | ObjStore of string
> end
> and IdSet: Set.S with type elt = Identity.id
>  = Set.Make(
>        struct
>  type t = Identity.id
>  let compare = Pervasives.compare
>        end)
>
> But for the life of me I can seem to use the "Id" variant type. How on
> earth do I create "Id" with a set of type id's other variances?
>
> In other words, if I wanted to use the variant Common for instance, I'll
> say: Common "some str value". How do I do this for Id, as in something
> like:
>     Id IdSet.add ([Common "C"; ObjStore "OS"] IdSet.empty)
>
> However, I've tried numerous variations of the above statement, and it's
> either complaining about a syntax error, or that type Common.Identity.id
> doesn't have a constructor - depending on where I place the parenthesis.
>
> Help!?
>
> Thank you,
> ==============================
> Jacques du Preez
>
> Web: OpenLandscape.net
> EMail: [email protected]
> Twitter: @jacquesdp
>
>
> On Sat, Jul 12, 2014 at 5:25 PM, Jacques du Preez <[email protected]>
> wrote:
>
>> Thank you so much Gabriel. I'll have a look at that. Thanks!
>>
>> ==============================
>> Jacques du Preez
>>
>> Web: OpenLandscape.net
>> EMail: [email protected]
>> Twitter: @jacquesdp
>>
>>
>> On Sat, Jul 12, 2014 at 5:20 PM, Gabriel Scherer
>> [email protected] [ocaml_beginners] <
>> [email protected]> wrote:
>>
>>>
>>>
>>> It is not correct to use the name of a compilation unit (.ml{,i} files)
>>> from within its own code: the cause of the circular dependency error here
>>> is the use of paths of the form Common.foo.
>>>
>>> To recursively define a type and sets over it, you should use recursive
>>> modules. This is actually the example given in the manual for recursive
>>> modules:
>>>   http://caml.inria.fr/pub/docs/manual-ocaml/extn.html#sec220
>>>
>>>
>>> On Sat, Jul 12, 2014 at 5:13 PM, Jacques du Preez [email protected]
>>> [ocaml_beginners] <[email protected]> wrote:
>>>
>>>>
>>>>
>>>> Hi,
>>>>
>>>> Please consider my common.mli:
>>>>
>>>> type id = | Id of Common.Id_set.t
>>>>           | Common of string
>>>>   | ObjStore of string
>>>>
>>>> module Id_set : (Set.S with type elt = id)
>>>>
>>>> Now my common.ml:
>>>>
>>>> type id = | Id of Common.Id_set.t
>>>>           | Common of string
>>>>   | ObjStore of string
>>>>
>>>> module Id_set = Set.Make(
>>>>     struct
>>>>       type t = id
>>>>       let compare = Pervasives.compare
>>>>     end)
>>>>
>>>> The above gives an circular build error. If I change Common.Id_set.t to
>>>> Id_set.t, then I get an unbound module error - I'm assuming this is because
>>>> the Id_set module declaration is after the variant declaration.
>>>>
>>>> What I'd like to know is, how would I change my Id variant to be of
>>>> type "id set"? Is this possible? The problem here is that Id_set depends on
>>>> variant id, and vice versa. How to solve this?
>>>>
>>>> Thanks,
>>>>
>>>> ==============================
>>>> Jacques du Preez
>>>>
>>>> Web: OpenLandscape.net
>>>> Twitter: @jacquesdp
>>>>
>>>>
>>>>
>>>
>>
>
>
> 
>