Re: [Caml-list] Higher order functors over tuples

[Ivan Gotovchits <ivg@ieee.org>]

Didier Cassirame <didier.cassirame@gmail.com> writes:

> Do you wish to have parallel computation done with these modules, or
> do you mean that you want them to be combined sequentially?

Ideally, computation must be combined arbitrary. It will be nice to have
MAP functor, or MAP2 functor, etc. 

> Thanks to a very recent post, I rediscovered that OCaml can handle modules as first class values (since ver. 3.12) :
>
> - you can define types based on module types like this.
>
> module type M = sig ... end
>
> type m = (module M)
>
> and then you should be able to build simple lists of type m.

I've heard that it is possible, but unfortunately I'm stucked with 3.11
;'( And I'm not still sure that it will work. Need to try it myself =)


>     3) My intution says that it can be solved with monads (Generator really
>     incapsulates side effects in a step. Several computation are combined in
>     one big chain... ). Am I right? If so, how to implement it in monads?
>
> I guess that you could use the type above with regular monads too.

Hmmm, the problem is that I do not understand monads quite well. So I've
solved the task in a «my» way. And so I want to know how the problem can
(and could it?) be solved with monads, which are considered a common and
idiomatic way of solving such problems.

>
> If you don't have access to that feature, you could perhaps use higher order functors?

I do use them. I generate a list of modules using higher order
functor. For example I build structure of modules [Even, Odd, Even, Odd] 
with 
   module M = Cons(Even)(Cons(Odd)(Cons(Even)(Odd)))

Calling ``let m = M.create ()'' will build some structure of objects of different
types. (Their can be more two types of modules). A call to ``M.step m''
will apply ``Even.step'' or ``Odd.step'' to the last objects in a list,
and move it to the head. A call ``M.result m'' will return the
result of calling ``Even.result m'' or ``Odd.result m'' dependingly on a
current type in head of list.

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