RE: [Caml-list] Cyclic type abbreviation

[David Allsopp <dra-news@metastack.com>]

Mr. Herr wrote:
> On 13.11.2015 13:49, Christoph Höger wrote:
> > Dear all,
> >
> > why is this type cyclic?
> >
> > type node = int * tree * tree
> >  and tree = node option
> >
> > I cannot introduce a manifest for the option type, as there is no
> > Option module (why is that, btw?) - so I would assume option to be
> > special enough to be handled like any other algebraic data type.
> type 'a option = None | Some 'a
> 
> no need for a module, just a simple type. Maybe you confound it with other
> languages.
> 
> And cyclic - well, the types are referring to each other.
> 
> Summary: what is supposedly wrong with it?

I expect that what is wrong is that you can write:

type node = int * tree * tree
 and tree = Some of node
          | None

I don't know why you can't write [and tree = node option] instead.


David