[Rd] 'CanMakeUseOf' field

[friedrich.leisch at stat.uni-muenchen.de]

> Duncan Murdoch <murdoch at stats.uwo.ca> writes:
>> I think we need an option to R CMD check rather than a new field in the
>> DESCRIPTION.  Currently a package could be mentioned for any of these
>> reasons:
>>
>> 1.  To make functions, examples or vignettes work
>> 2.  To allow optional functionality in functions, examples or vignettes.
>> 3.  Because it contains complementary functions.
>>
>> I don't think we really need to worry about 3:  it should be contained
>> in 1 or 2, if reasonably complete examples are given.
>>
>> Case 1 is handled by Depends.
>
> I think there is an important distinction between a dependency needed
> for the package to function and a dependency needed to demonstrate
> said functionality via an example or vignette.  The former is what
> Depends is about, the latter is something else (Suggests).

Sorry to join in late, I am at the Compstat conference and have limited
email access. What Seth describes in the above paragraph is exactly what I
had in mind when splitting the single Depends field we had into Depends
and Suggests: Depends are a necessity to run the package, Suggests is nice
to have but not necessary. If you know how to use a package you may the
decide not to install a package that is only suggested, but

  * may not be interested to execute the examples,
  * know that you never need the extra functionality
  * ...

so it should not be auto-installed unless you ask for it (the default
could also be the other way round, the point is that it should be possible
to have package foo but not the packages it only suggests). On CRAN we
check with all suggestions to test all bits and pieces, having an option
in R CMD check to test only with suggests may be nice, if there is use for
it.

Ad the wording in the manual: obviously that is not optimal (otherwise no
need for parts of this email thread), perhaps somebody else than the
original author (=me) could try to improve it for 2.4 after this
clarifications?  Otherwise I will give it a shot next week after I return
from Rome.

Best,
Fritz