'CanMakeUseOf' field

Duncan Murdoch wrote:

On 8/29/2006 2:24 PM, Paul Gilbert wrote:

Seth Falcon wrote:

Duncan Murdoch <murdoch at stats.uwo.ca> writes:
 

On 8/29/2006 11:58 AM, Seth Falcon wrote:
  

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).
    

Yes, that's a good point, especially with vignettes.  Only the package
author needs to be able to run them.
  

Yes, but just to keep things clear: the value of vignettes is that
users can follow along.  So the ability to programatically identify
the extra required packages is valuable.

 

But maybe examples should be considered broken if they don't
work. Users should be able to expect example(foo) not to generate an
error.  Package authors should wrap optional examples in code like if
(require(...)).
  

This is a work around that is ok for the developer's testing and to 
prevent failure on CRAN, and I use it. But, other than actually 
reading the examples, it provides no hints to other testers or users 
about things that might be installed, or installed first, to give 
more complete testing and more functionality.

I'm not saying to use this instead of Suggests, I'm saying to do both. 
This way the Suggests entries really are suggestions:  the examples 
will run with or without the presence of the suggested packages.

I think there are so many variations on when a Suggested package 
should be installed, that it's not reasonable to expect to be able to 
encode them all in a machine readable way.  They should be documented 
in human readable format.

Looking toward the future, I think it would be useful to have a 
standard mechanism to indicate extensions that are available in a 
package, and might be tested and used, but are not necessarily 
available on CRAN. For instance, an example might access to a 
purchased database or take advantage of  a computer cluster. It seems 
limiting to think that all testing that cannot be done on CRAN must 
be done almost exclusively by the developer.

If by "mechanism" you mean human-readable documentation, I agree with 
this.

Yes,  I was think of human-readable and in a standard location, like a 
field in the DESCRIPTION file.  (You are thinking of fields in the 
DESCRIPTION file as human-readable, are you not?)

Paul

Duncan Murdoch

Paul

I agree.  As with vignettes, there is value in users being able to
follow along and it would be nice to have a programatic way to
identify extra package needed for fancy/involved/optional examples.

Best,

+ seth

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