[Rd] 'CanMakeUseOf' field

[Duncan Murdoch]

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.

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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>>  
>>
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