[Rd] clarification of library/require semantics

[Robert Gentleman]

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