[prog] Converting definitions into 'on the fly' code... And GPL query

[Conor Daly]

On Fri, May 14, 2004 at 08:00:20PM +1000 or thereabouts, Rasjid Wilcox wrote:
> On Thursday 13 May 2004 23:51, Conor Daly wrote:
> >
> > I've spent the last 4 days hacking on this in an attempt to understand it
> > and I think I've got it now.  Looks pretty damn good to me.  I haven't
> > figured out yet how the self.equation bit works yet (it does, I just don't
> > know how...).  I'm going off to present this as a sample to the project
> > leader now.

Who was mightily impressed...
 
> You are more than welcome to ask questions.
> 
> Also, if you have not worked out how to read the index table only once (at 
> class initialisation time) rather than for each record, let me know.  It 
> should only be around a 5 line change, and pretty simple.

Chances are we will end up using a temporary (or should I say non-permanent)
table containing a data 'heap'.  This will likely end up with columns named
to correspond to the variable names in the equations.  
 
> Lastly, did you note the change I made to allow the use of mutli-line tests 
> that can utilise their own variables?  It makes the system substantially more 
> powerful and flexible, without making it any more complex for the current 
> case.  (Current style tests are just prefixed with 'result = '.)

I saw but wasn't quite clear on how it's used.  In any case, this is
currently a prototype sample and will be significantly refined before
production.

One thing that came to mind was:  "What if the minute data is missing?".
Currently the _sumOverDate() function returns 0 if there's no data.  Can one
return NULL or some other something that will cause 'eval(self.equation)' to
return false?  The instance could arise where 'rrr - _sumOverDate('r',
'minute'...)' will have a valid rrr=0 and _sumOverDate() return 0 'cos
there's no data so the eval() will return true which would be an error.

That lead to a discussion on whether the tests should know whether there
should be a particular data set (eg. some stations report only hourly
rainfall so there'll be no minute rain from them) and should return a 'pass'
instead of a 'fail'.  My view is that the program should decide whether it's
appropriate for a particular test to run ("should we have minute rain?"  "Do
we have minute rain?" ...) rather than the test itself.
 
> > On a side note, you've put your code in the public domain.  Can I
> > subsequently incorporate that in a GPL application so that it now falls
> > under the GPL?  I presume I can.
> 
> Absolutely.  You can do with it as you wish - there is not even any need for 
> attribution (although I would not complain).
> 
> It was meant as a code sample, and I wanted it to be able to be freely 
> incorporated whereever it may be useful - even in a closed source 
> application.  You can certainly put it in a GPL application.
> 
> I guess I could have put it under a BSD license and achieved more or less the 
> same effect.  But given the nature of the code I felt that putting it into 
> the public domain was cleaner.
> 
> Hmmm.... any license guru's out there that want to comment on the pro's and 
> con's of public domain vs modified BSD?

The other interesting licensing question is in the other direction.
Assuming I have released a GPL application.  Someone wants to use it but in
a proprietary application which the GPL won't allow.  They contact me and
ask to license my application to them for proprietary use.  Can I construct
a license that requires them to:  

o Acknowledge the existence of code that is also available under GPL
o Provide the standard GPL 'offer of source' for my code

without having to GPL their proprietary extensions.  Of course I can, but is
it in any way useful for me to do this?

Conor
-- 
Conor Daly,                   Please avoid sending me 
Met Eireann, Glasnevin Hill,  Word or PowerPoint attachments.
Dublin 9, Ireland             http://www.fsf.org/philosophy/no-word-attachments.html
Ph +3531 8064276 Fax +3531 8064247


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