On Tue, 27 Oct 2015, oleg_komashko@ukr.net wrote:

> Dear Allin, Thank you for comprehensive answer. I have experience 
> in learning some soft by experiments, so I hope to be useful in 
> finding undocumented hacks to be excluded

Thanks, that's helpful!

> P.S. Sorry for inaccurate line:
>
> eval isnull(varname(somelist)
>
> This works:
>
> nulldata 1
> list nlist = null
> z = isnull(varname(nlist))
> z
>
> Another hack or legal?

Note, the output from the above is:

<output>
? nulldata 1
periodicity: 1, maxobs: 1
observations range: 1 to 1
? list nlist = null
Generated list nlist
? z = isnull(varname(nlist))
Generated scalar z = 1
? z
1
Done
</output>

Well, it's certainly an oddity but it is legal, and if you think it 
through it is consistent with the documentation for isnull(). The 
expression "varname(nlist)" produces an empty string -- in 
conformity with its documentation, since nlist is empty. But the 
empty string is not the name of any existing variable, so 
isnull(<empty string>) correctly returns 1 (!).

Allin
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