R devel - Nov 2005 - clarification of library/require semantics

Recently I have added a lib.loc argument to require, so that
it is more consistent with library. However, there are some oddities 
that folks have pointed out, and we do not have a documented description 
of the semantics for what should happen when the lib.loc parameter is 
provided.

   Proposal: the most common use case seems to be one where any other 
dependencies, or calls to library/require should also see the library 
specified in the lib.loc parameter for the duration of the initial call 
to library. Hence, we should modify the library search path for the 
duration of the call (via .libPaths).

  The alternative, is to not do that. Which is what happens now.

  Both have costs, automatically setting the library search path, of 
course, means that users that do not want that behavior have to manually 
remove things from their library. But if almost no one does that, and 
most folks I have asked have said they want the lib.loc parameter to be 
used for other loading.

   Comments?

  Robert

-- 
Robert Gentleman, PhD
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M2-B876
PO Box 19024
Seattle, Washington 98109-1024
206-667-7700
rgentlem at fhcrc.org

On Fri, 4 Nov 2005, Robert Gentleman wrote:
> Recently I have added a lib.loc argument to require, so that
> it is more consistent with library. However, there are some oddities
> that folks have pointed out, and we do not have a documented description
> of the semantics for what should happen when the lib.loc parameter is
> provided.
>
>   Proposal: the most common use case seems to be one where any other
> dependencies, or calls to library/require should also see the library
> specified in the lib.loc parameter for the duration of the initial call
> to library. Hence, we should modify the library search path for the
> duration of the call (via .libPaths).
>
>  The alternative, is to not do that. Which is what happens now.
>
>  Both have costs, automatically setting the library search path, of
> course, means that users that do not want that behavior have to manually
> remove things from their library. But if almost no one does that, and
> most folks I have asked have said they want the lib.loc parameter to be
> used for other loading.
>
>   Comments?
There is a parallel set of issues with loadNamespace and the dependent 
namespaces it loads.  I think I would want the same semantics (whatever 
they are) for loadNamespace and library.

I set my standard libraries in R_LIBS, so when I use lib.loc it is for 
experimental things.  So I would neither want the .libPaths changed nor 
be affected if they were.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595