Re: [Caml-list] CDK license

[Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>]

From: "Stefan Monnier" <monnier+lists.caml/news/@rum.cs.yale.edu>
> >>>>> "Dave" == Dave Berry <Dave@kal.com> writes:
> > I would encourage people to use an X/BSD-like license for code
> > whereever possible.  This license allows anyone to do anything whatsoever
> > with the code, provided that they keep the copyright notice and NO
> > WARRANTY notice.  It saves you all this hassle with determining what is
> > and is not allowed, and which code may be linked or distributed with which
> > other code.
> 
> You seem to be talking about the original BSD license.  Note that in that
> license, the requirement to keep the copyright notice makes it incompatible
> with the GPL license (which is why there is a revised BSD license which
> does away with the "keep the copyright notice" part).

The X license does not contain that clause, so I suppose that by X/BSD
he meant the revised BSD license already, which is certainly the
most free license you can imagine, the next step being public domain.

I also like BSD very much, but using it requires everybody agreeing on
such a free license, while as Sven points out it includes the possibility
of non-cooperative behaviour.
LGPL was choosen for ocamlrun, to specifically forbid this. You can
include the ocaml runtime in an ocaml program, but you cannot make
modifications to it to serve a different purpose without publishing them.
As a result, it is used for everything else in the system, since any
executable will depend on parts of the ocaml runtime anyway.
(If it is switched to BSD someday, I'll certainly switch all my
libraries to BSD also, after checking with contributors. I would honestly
prefer it for simplicity.)

Yet, I think the LGPL is reasonably balanced. It tries to protect the
code itself (which BSD does not really), while not (much) restricting
its use.

The subtle part, as has already been discussed on this list, is
section 6 of the LGPL, about linking, which I reproduce below.
Outside of the problem that the condition may cause incompatibilities
with licenses of other libraries (if they prohibit reverse engineering
for instance), there is a difficulty with changes in the format of
.cmi or .cmx files between versions.
Basically, section 6 says that if you do not publish source code, then
when asked you should provide a link-kit for your program allowing to
rebuild the executable from modified versions of the runtime and
libraries protected by the LGPL.  But since almost every version of
ocaml has a different format for the .cmi, one reading would be that
you have to provide a link-kit for every new version of ocaml. This
seems utterly impractical. Writing it somewhere explicitly might be
useful. Something like: "The work in binary form described in section
6 is to be understood as compiled by a specific version of ocaml. You
are not liable to provide it for other versions." This looks like it
is already included in the provisions about changes in the text of the
interface, but the problem is that incompatibilities can be created
without changing the source code. (By the way I'm sure that nobody
ever produced such a link-kit. But did anybody distribute
closed-source caml software?)

Sven had also concerns with section 5, particularly about the use of
functors understood as derivative work. This may be related to the
problem with templates in C++. However, functors in caml do not imply
recompilation for each use, so I think this is not a problem. There is
also inlining, but ocaml does not do much more inlining than C, for
which it is considered OK. As a result I think that there is no real
need to explicitly say that ocaml linking is to be understood as
linking.

The GNAT approach which Brian presented, of taking the GPL but
allowing linking unconditionally, is more liberal than LGPL, and
avoids these problems.  You don't have to provide a link-kit for your
executable.
This would make things much simpler, but I'm not sure it covers the
original goal of using the GPL: wouldn't it allow one to include
modified versions of the runtime in an executable, without publishing
the changes?

Regards,

Jacques Garrigue

----------
Extract from LGPL version 2

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