About namespaces

About namespaces

[David Rajchenbach-Teller]

At the moment, there is no difference between modules and namespaces.
Among other things, this means that if I write an extension MyList to
List and someone else writes and extension HisList to List, there is no
automated way to merge these, I need to write yet another module
LatestList to be able to use both extensions at the same time. While
this is certainly possible, it's also quite clumsy and prevents drop-in
additions to existing modules (or hierarchies, yes) by third-party
libraries, something which, as Richard Jones points out, may be
important.

All of this is due to the fact that modules are closed: once a module
has been written, there is no way to add something to that module
without altering the source code or writing a new module.

Now, David Allsopp suggested (off-list) that we could perhaps implement
namespaces as a Camlp4 extension, with the use of external configuration
files (something which can already be managed with findlib). I'm
shamelessly forwarding his idea and asking for feedback.

Where we have [open List] to open one specific module called [List], we
could introduce
* [use List] to open all the modules registered as providing namespace
[List]
* [import List] to locally rebind [List] to a module obtained by
including all the modules registered as providing namespace [List]

In each case, finding out which modules are registered as providing
namespace [List] is performed statically, by Camlp4 reading a set of
external configuration files.

What do you think?

Cheers,
 David
-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act brings liquidations. 

Re: [Caml-list] About namespaces

[Christophe Raffalli]

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And what about include (it is your import) ? It allows what you want and
is short ?


module Mylist = struct
  let id x = x
end

module Hislist = struct
  let id2 x = x
end

module Alllist = struct
  include Mylist
  include Hislist
end

What is really missing is renaming when opening or doing include (with
regular expression pattern matching for instance).

Cheers,
Christophe


-- 
Christophe Raffalli
Universite de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tel: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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Re: [Caml-list] About namespaces

[David Rajchenbach-Teller]

On Thu, 2008-11-20 at 22:57 +0100, Christophe Raffalli wrote:
> And what about include (it is your import) ? It allows what you want and
> is short ?

No, [include] is the low-level mechanism which must be used to implement
the higher-level [import]. The main difference being that [import] needs
to read information from all the (findlib) packages which are being used
to compile your project and determine all the modules from each package
which are registered as providing [List]. The programmer doesn't need to
know the exact name of each module.

Does that make things any clearer?

Cheers,
 David


-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act brings liquidations. 

Re: [Caml-list] About namespaces

[Ashish Agarwal]

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> Among other things, this means that if I write an extension MyList to
> List and someone else writes and extension HisList to List, there is no
> automated way to merge these, I need to write yet another module
> LatestList to be able to use both extensions at the same time.


Merging these with the import command you propose requires an external
configuration. Would that be any easier than using include to define a new
module? Or is there supposed to be some other benefit I'm missing?

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