RE: [Caml-list] about typedefs... (was: duplication implementation/interface)

RE: [Caml-list] about typedefs... (was: duplication implementation/interface)

[Manuel Fahndrich]

Yes, the reason it is needed is to be able to export from a module both
a type sharing constraint, and at the same time the concrete type
representation.

module type I = sig
  module M : J

  type t = M.s = { foo : int }
end

Such a description gives you two pieces of information. M.s = t and also
the representation of this type.

Regards,

	Manuel

-----Original Message-----
From: Olivier Andrieu [mailto:andrieu@oxygene.ijm.jussieu.fr] 
Sent: Thursday, March 22, 2001 3:17 AM
To: caml-list@inria.fr
Subject: Re: [Caml-list] about typedefs... (was: duplication
implementation/interface)

 Judicael Courant [Thursday 22 March 2001] :
 > Brian Rogoff a écrit :
 > > 
 > [...]
 > > What's the problem with the hack I suggested earlier: put the
 > > huge variant (and other duplicated types) in a "pure" .mli file
 > > (I hate using .ml for that) and "open"ing it where you need it,
 > > once in the .mli file and once in the .ml file? This way you
 > > reduce the duplication to two lines.
 > > 
 > > I know some people are open-phobes, but I find this use of open
 > > to be acceptable.
 > > 
 > 
 > As for open-phobes, somebody gave me a good solution a few days
 > ago: you can locally define a module with a very short name.

There's something I've been wondering about type definitions :

In type definitions, you can specify type equation and representation.
 - when none is specified, the defined type is abstract ;
 - when an equation is given, you get an alias of an already existing
type ;
 - with a representation, a new variant or record is defined.

But it is possible to use both, so that you get an alias of an already
defined variant and record but with the fields or constructors attached
to
the new type. 

It don't really see the point of such a definition : now the type
representation is in 4 different places, and the only gain I see is
that you don't have to prefix the fields names with a module
path. That's no big deal since you can redefine the module with a short
name (one letter).

So, is this form of type definitions actually used, does it have another
purpose besides this namespace issue ?

	Olivier
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Re: [Caml-list] recursive modules redux, & interface files

[Brian Rogoff]

On Wed, 21 Mar 2001, Patrick M Doane wrote:
> I don't see that it makes much of a difference. Besides, the reason it
> hasn't worked well for me is that inevitably I want to add some
> functions to the module that has the variant type. For example, pretty
> printers. The next compromise is to continue the path without a .mli file
> until I don't want some of these utilities to be exported.  In the end,
> I'm back to the source of the problem, having to duplicate a large variant
> type.

What's the problem with the hack I suggested earlier: put the huge variant 
(and other duplicated types) in a "pure" .mli file (I hate using .ml for
that) and "open"ing it where you need it, once in the .mli file and once in the 
.ml file? This way you reduce the duplication to two lines.

I know some people are open-phobes, but I find this use of open to be 
acceptable.

-- Brian

> 
> On Thu, 22 Mar 2001, John Max Skaller wrote:
> 
> > Patrick M Doane wrote:
> >  
> > > For projects that I've worked on that have huge variant types, I have
> > > typically placed the variants in a module by themselves with no .mli file.
> > > This technique hasn't worked too well for me in practice and is still
> > > annoying for the smaller variants.
> > 
> > 	Try placing them in a .mli file instead (no ml file).
> > 
> > -- 
> > John (Max) Skaller, mailto:skaller@maxtal.com.au
> > 10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
> > checkout Vyper http://Vyper.sourceforge.net
> > download Interscript http://Interscript.sourceforge.net
> > 
> 
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Re: [Caml-list] duplication implementation/interface

[Judicael Courant]

Brian Rogoff a écrit :
> 
[...]
> What's the problem with the hack I suggested earlier: put the huge variant
> (and other duplicated types) in a "pure" .mli file (I hate using .ml for
> that) and "open"ing it where you need it, once in the .mli file and once in the
> .ml file? This way you reduce the duplication to two lines.
> 
> I know some people are open-phobes, but I find this use of open to be
> acceptable.
> 

As for open-phobes, somebody gave me a good solution a few days ago: you
can locally define a module with a very short name.

Example : put your type in my_beautiful_type.mli with constructors Node,
Leaf, ..., and where you need it do

module T = My_beautiful_type

then you can use it with a small overhead of 2 chars per use of a
constructor of My_beautiful_type: T.Node, T.Leaf, ...

This is quite elegant IMHO as it makes your code very clear.

As an aside, if you consider applying the same treatment for exceptions
(also duplicated), you need to put them in a .ml file (not a .mli) as a
.cmo is needed for linking (an exception actually creates at run-time a
fresh exception identifier).

Judicaël
-- 
Judicael.Courant@lri.fr, http://www.lri.fr/~jcourant/
(+33) (0)1 69 15 64 85
"Montre moi des morceaux de ton monde, et je te montrerai le mien"
Tim, matricule #929, condamné à mort.
http://rozenn.picard.free.fr/tim.html
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Re: [Caml-list] about typedefs... (was: duplication implementation/interface)

[Olivier Andrieu]

 Judicael Courant [Thursday 22 March 2001] :
 > Brian Rogoff a écrit :
 > > 
 > [...]
 > > What's the problem with the hack I suggested earlier: put the
 > > huge variant (and other duplicated types) in a "pure" .mli file
 > > (I hate using .ml for that) and "open"ing it where you need it,
 > > once in the .mli file and once in the .ml file? This way you
 > > reduce the duplication to two lines.
 > > 
 > > I know some people are open-phobes, but I find this use of open
 > > to be acceptable.
 > > 
 > 
 > As for open-phobes, somebody gave me a good solution a few days
 > ago: you can locally define a module with a very short name.

There's something I've been wondering about type definitions :

In type definitions, you can specify type equation and representation.
 - when none is specified, the defined type is abstract ;
 - when an equation is given, you get an alias of an already existing
type ;
 - with a representation, a new variant or record is defined.

But it is possible to use both, so that you get an alias of an already
defined variant and record but with the fields or constructors attached to
the new type. 

It don't really see the point of such a definition : now the type
representation is in 4 different places, and the only gain I see is
that you don't have to prefix the fields names with a module
path. That's no big deal since you can redefine the module with a short
name (one letter).

So, is this form of type definitions actually used, does it have another
purpose besides this namespace issue ?

	Olivier
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