Re: [Haskell-cafe] oauth in haskell - reviewers?

robgreayer:

On Mon, Aug 24, 2009 at 5:24 PM, Don Stewart wrote:

...

I notice hoauth is packaged as LGPL. Since we use static linking in GHC, this makes it in practice GPL. Is that the intent?

-- Don

I don't think this is 100% true -- the requirement is to allow the end user the ability to replace the version of the library they're using with something else, which can be accomplished by dynamically linked libraries, but also means that if the rest of the program is open source (but not GPL), the requirement is satisfied. LGPL is generally compatible with GPL-incompatible open-source, whether statically linked or not. It is true it is incompatible with closed source licensing.

There are some real situations where this might matter -- you could use this library in an an executable in which the remainder of the source was MPL, I think, as long as there were the possibility of relinking with a different version of the LGPL library. You couldn't do this if it were GPL. This is the section of the LGPL that mentions this:

"Do one of the following:

* 0) Convey the Minimal Corresponding Source under the terms of this License, and the Corresponding Application Code in a form suitable for, and under terms that permit, the user to recombine or relink the Application with a modified version of the Linked Version to produce a modified Combined Work, in the manner specified by section 6 of the GNU GPL for conveying Corresponding Source. *1) Use a suitable shared library mechanism for linking with the Library. A suitable mechanism is one that (a) uses at run time a copy of the Library already present on the user's computer system, and (b) will operate properly with a modified version of the Library that is interface-compatible with the Linked Version."

So, Haskell libraries licensed under LGPL (without the static linking exception) force option 0, but that doesn't make them completely equivalent to GPL. At least that's my understanding (which could be flawed!).

That's quite true. It's not completely equivalent. It is just very difficult to distribute your Haskell app in such a way that it can be relinked against LGPL licensed Haskell libraries. If the intent is that the improvements to the source remain open, and are contributed back, but you want to allow commercial use, a different license would be appropriate. -- Don