Some questions about signatures

Some questions about signatures

[Juan Jose Garcia Ripoll]

Hi,

I must admit that I'm more fluent in SML than in OCaml and that's the reason
for these questions.

1) Are OCaml's signatures opaque? I mean if they do hide the real
implementation of data types and of non-declared values to the public, much
like SML's :>

2) How can I extend a signature with new values and types? I've been using the
'include' directive, but I did not find it in the manual. Is this supposed to
work or is it just a Caml-Light reminiscent.

3) What is the simplest way to build toplevel modules using functors? In SML
everything on every file is bound to the toplevel environment and one can do
just 'structure NewStruct = AFunctor(structure A = AParameter)' to get a brand
new module. But in OCaml toplevel modules are defined in term of two files
(mli/ml) so what are my options if I dont want to add a spurious path name?

Regards
	Juanjo

-- 
Juan Jose Garcia Ripoll		www: http://www.arrakis.es/~worm
Dpto. de Matematicas		job: jjgarcia@ind-cr.uclm.es
E.T.S.I. Industriales		home: worm@arrakis.es
Univ. de Castilla-La Mancha, Ciudad Real E-13071 (Spain)

Re: Some questions about signatures

[Xavier Leroy]

> 1) Are OCaml's signatures opaque? I mean if they do hide the real
> implementation of data types and of non-declared values to the public, much
> like SML's :>

Yes, they are.  OCaml's ": SIG" construct behaves like ":> SIG" in
SML'97.

> 2) How can I extend a signature with new values and types? I've been
> using the 'include' directive, but I did not find it in the
> manual. Is this supposed to work or is it just a Caml-Light
> reminiscent.

No, it's an oversight in the manual.  "include" in signatures was
originally an experimental feature, but it seems useful enough that it
will stay.  I'll fix the manual.

> 3) What is the simplest way to build toplevel modules using
> functors? In SML everything on every file is bound to the toplevel
> environment and one can do just 'structure NewStruct =
> AFunctor(structure A = AParameter)' to get a brand new module. But
> in OCaml toplevel modules are defined in term of two files (mli/ml)
> so what are my options if I dont want to add a spurious path name?

Currently, you must put your functors inside toplevel structures,
which are then mapped to .ml/.mli files.  So, continuing your example
above, you have to write

        module NewStruct = ModA.Functor(AParameter)

or
        open ModA
        module NewStruct = Functor(AParameter)

One could imagine having compilation units that can be functors by
themselves.  It's mostly a problem of syntax: currently, the contents
of an implementation file (.ml) are systematically taken to be the
inside of a "module X = struct ... end" declaration;  extending this
to functors would require special syntax for the parameters.

Regards,

- Xavier Leroy