[Haskell-cafe] GPL answers from the SFLC (WAS: Re: ANN: hakyll-0.1)

minh thu noteed at gmail.com
Thu Mar 4 12:55:30 EST 2010

2010/3/4 Tom Tobin <korpios at korpios.com>:
> After politely pestering them again, I finally heard back from the
> Software Freedom Law Center regarding our GPL questions (quoted
> below).
> I exchanged several emails to clarify the particular issues; in short,
> the answers are "No", "No", "N/A", and "N/A".  The SFLC holds that a
> library that depends on a GPL'd library must in turn be GPL'd, even if
> the library is only distributed as source and not in binary form.
> They offered to draft some sort of explicit response if we'd find it
> useful.
> Maybe it would be useful if Cabal had some sort of licensing check
> command that could be run on a .cabal file, and warn an author if any
> libraries it depends on (directly or indirectly) are GPL'd but the
> .cabal itself does not have the license set to GPL.
> On Fri, Dec 11, 2009 at 10:21 PM, Tom Tobin <korpios at korpios.com> wrote:
>> I'd like to get these questions out to the SFLC so we can satisfy our
>> curiosity; at the moment, here's what I'd be asking:
>> Background: X is a library distributed under the terms of the GPL. Y
>> is another library which calls external functions in the API of X, and
>> requires X to compile.  X and Y have different authors.
>> 1) Can the author of Y legally distribute the *source* of Y under a
>> non-GPL license, such as the 3-clause BSD license or the MIT license?
>> 2) If the answer to 1 is "no", is there *any* circumstance under which
>> the author of Y can distribute the source of Y under a non-GPL
>> license?
>> 3) If the answer to 1 is "yes", what specifically would trigger the
>> redistribution of a work in this scenario under the GPL?  Is it the
>> distribution of X+Y *together* (whether in source or binary form)?
>> 4) If the answer to 1 is "yes", does this mean that a "BSD-licensed"
>> library does not necessarily mean that closed-source software can be
>> distributed which is based upon such a library (if it so happens that
>> the library in turn depends on a copylefted library)?
>> By the way, apologies to the author of Hakyll — I'm sure this isn't
>> what you had in mind when you announced your library!  I'm just hoping
>> that we can figure out what our obligations are based upon the GPL,
>> since I'm not so sure myself anymore.


Great to have the answer but it's confusing to me...

The next question that comes to mind is thus:
What if a new library X' released under BSD or MIT license implements
the X API (making possible to compile Y against it)? Can such a new
library X' be licensed under something else than the GPL (we guess Yes
because we don't think it is possible to license the API itself)? Why
should the existence of X' make any difference for the author of Y?


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