As usual: For legal advice, get a lawyer... However, yes, the GPL quite
expressedly allows licencees to distribute modified versions, provided that the
modified source code is made available and is redistributable under the GPL.
It's common courtesy and possibly also required by law (the GPL itself
doesn't say anything about it) to ensure that the original statements of
authorship and copyright are retained.
One thing to be slightly cautious about is to avoid inadvertent copyright
transfer to your publisher of things that are also in the package. The back
pages of ISwR (the book) has copies of the help pages for ISwR (the package),
but "Reproduced with permission" so that Springer doesn't have the
copyright for that part of the book. Not that they are likely to care, but
better safe than sorry.
-Peter D
On 04 Mar 2014, at 16:50 , Michael Friendly <friendly at yorku.ca> wrote:
> There is a CRAN package licensed just as "GPL", say, XX, I want
to use in a book.
> But I've needed to modify the package to make it do what I need for
expository purposes.
> The package author(s) are amenable to my modifications, but probably
unlikely to
> incorporate them into the CRAN version any time soon.
>
> Am I allowed, under GPL, to create a new version of the package, say XX2,
in a
> public repository such as R-Forge or github? I would, of course, maintain
their
> authorship, though perhaps take over the maintainer role. For my purposes
in
> the book, I don't necessarily need to release my version to CRAN; just
a public repo
> a reader could download from.
>
> -Michael
>
> --
> Michael Friendly Email: friendly AT yorku DOT ca
> Professor, Psychology Dept. & Chair, Quantitative Methods
> York University Voice: 416 736-2100 x66249 Fax: 416 736-5814
> 4700 Keele Street Web: http://www.datavis.ca
> Toronto, ONT M3J 1P3 CANADA
>
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--
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com