HJW wrote
> >It seems I encountered an inconsistency between Stata 6 and
> >7, and I would like to ask for help. Say I have a program
> >like the follows.
> >
> > program define myexpl
> > version 6.0
> > syntax ...., ..... [myopt(varlist) .... ]
> >
> > end
> >
> >In Stata 7, if I issue the command,
> >
> > myexpl ....., myopt() /* empty in -myopt- */
> >
> >then Stata will return empty for `myopt' in the program,
> >which is what I want. However, if the same program runs
> >under Stata 6, then Stata complains with the message:
> >
> > myopt() is invalid
> >
> >I know Stata 6 probably expects variable names in -myopt-,
> >so when no name is given it complains. However, I need the
> >behavior of Stata 7; is there any way to let Stata 6 behaves
> >like its next generation does? Something like default=none
> >may do, but this does not seem to work on options. Can
> >anyone help? Thanks in advance.
> >
> >[Just for those curious: I know his situation is odd,
> >because if an empty string is desired, why specify the
> >option -myopt- in the first place? Well, this is a part of a
> >complicated maximum likelihood program, which estimates
> >several different models. In order to preserve syntax
> >consistency across models, -myopt- is required if a
> >particular model is called, no matter whether it eventually
> >contains a varlist or an empty string. Alright, this may be
> >my own eccentric programing style, but please spare me with
> >the eccentricity.]
and Roger Newson replied
>
> In the calling program, you can define a local macro equal to
> -myopt(varlist)- if the varlist is non-empty, and equal to
> an empty string
> otherwise. For instance, if the varlist is in a macro
> -vlist-, then you
> might have some lines, in your calling program, as follows:
>
> local myoptv ""
> if "`vlist'"!="" {
> local myoptv "myopt(`vlist')"
> }
> myexpl,`myoptv'
>
> and -myexpl- will be called with the -myopt- option if, and
> only if, the
> macro -vlist- is non-empty.
I am not clear about several aspects of this problem.
For example, what is meant exactly by running under
version 6? There is a big difference between
(a) running a Stata 7 executable and within that
running a program with a -version 6.0- statement.
(b) running a Stata 6 executable.
The two are not equivalent. Under (a) Stata 7
does _not_ forget all that it knows about Stata
7.0 syntax changes.
I suspect it is not that
> Stata 6 probably expects variable names in -myopt-,
> so when no name is given it complains.
Rather the problem is that Stata 6.0 (strong sense)
just does not understand the syntax of your
-syntax- statement. How could it?
Roger's solution seems to suppose that you
have a Stata 7 executable and want to run
a program with -version- set to 6.0. I
am not clear that that is your situation.
One way to do what you want might be to let -myopt()-
take a string within -syntax- and to do processing
of any supplied string argument using -unab-.
Other elements being understood,
version 6.0
syntax , [myopt(str)]
if "`myopt'" != "" {
unab myopt : `myopt'
}
Nick
[email protected]
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