Re: st: Programming Problem: How to prevent macro substitution

[Christoph Birkel <christoph.birkel@soziologie.uni-halle.de>]

Eva, Nick,

thank you for your advice! I will try to transfer the generation of the 
temporary variables into the loop which generates the macro, and follow  
the suggestion of Nick, which seems to  work well. Again: Many thanks!

Best,

Christoph

Eva Poen schrieb:


> Nick, thank you.
>
> I was looking for a solution that can be done independently of the
> creation of the temporary variables, since this is how Christoph
> started the thread. What I didn't realise is that my solution will
> contain the interior double quotes, which a simple -display- will not
> reveal:
>
> . local test "hello " "hello"
>
> . di "`test'"
> hello hello
>
> . di `"`test'"'
> hello " "hello
>
> It is therefore clearly not suitable, and plainly wrong. Thanks for
> pointing it out to me. Austin gave a perfect, working solution.
>
> I also agree that escaping macro substitution is often not the way
> forward. At least I have managed to avoid it completely in my work.
>
> Eva
>
>
> 2008/7/16 Nick Cox <n.j.cox@durham.ac.uk>:
>  
>
> > I see. Well, there will be an almost equally simple way of doing that,
> > or an equivalent, and one which certainly won't entail escaping macro
> > substitution.
> >
> > For example, suppose you are in a loop
> >
> > Within some loop {
> >       ...
> >       tempvar foo
> >
> >       local xlist `xlist' i.land|`foo'
> >       ...
> > }
> >
> > Otherwise put, I don't think there is ever a problem for which lines
> > like
> >
> >       local ldep`u' "ldep`u'"
> >
> > are part of the solution.
> >
> > (We had a similar thread a while back in which someone asserted that it
> > was sometimes necessary to delay substitution, and I kept disputing
> > that. It's a myth that seems to grow out of trying to translate other
> > programming styles to Stata macro programming.)
> >
> > Nick
> > n.j.cox@durham.ac.uk
> >
> > Eva Poen
> >
> > Thanks, Nick.
> >
> > However, your suggestion does not produce the desired result:
> >
> > . di "`xlist'"
> > i.land|ldep0 i.land|ldep1 i.land|ldep2
> >
> > While Christoph was after:
> >
> > . di "`xlist'"
> > i.land|`ldep0' i.land|`ldep1' i.land|`ldep2'
> >
> > Unless I am missing something here.
> >
> > Eva
> >
> > 2008/7/16 Nick Cox <n.j.cox@durham.ac.uk>:
> >
> >    
> >
> > > I agree. In fact, I'd go one step further:
> > >
> > > foreach u of numlist 0/2{
> > > local xlist `xlist'  i.land|ldep`u'
> > > }
> > >
> > > Sometimes the quotes just make things more complicated.
> > >      
> > Eva Poen
> >
> >    
> >
> > > take it in steps and it works:
> > >
> > > foreach u of numlist 0/2{
> > > local xlist "`xlist' " "i.land|" "`" "ldep`u'" "'"
> > > }
> > >
> > >
> > > -di "`xlist'"- returns
> > >
> > > i.land|`ldep0' i.land|`ldep1' i.land|`ldep2'
> > >
> > > on my machine.
> > >
> > > 2008/7/16 Christoph Birkel <christoph.birkel@soziologie.uni-halle.de>:
> > >
> > >      
> > >
> > > > I want to program a loop which produces a macro `xlist' containing a
> > > >        
> > > list of
> > >      
> > >
> > > > dummy variable interaction expansion expressions with temporary
> > > >        
> > > variable
> > >      
> > >
> > > > names `ldep0' , `ldep1' etc. as a string . For this purpose I wrote:
> > > > foreach u of numlist 0/`y2'{
> > > > local ldep`u' "ldep`u'"
> > > > local xlist "`xlist' i.land|``ldep`u'''"
> > > > }
> > > > The resulting macro should contain an expression like "
> > > >        
> > i.land|`ldep0'
> >    
> >
> > > > i.land|`ldep1'  i.land|`ldep2' "  (when  `y2'  contains 2)  which
> > > >        
> > > can be
> > >      
> > >
> > > > used as argument in -xi: reg-, as in: xi: reg yvar i.land `xlist' .
> > > >        
> > > (The
> > >      
> > >
> > > > temporary variables `ldep0' and so on, corresponding to the macros
> > > >        
> > are
> >    
> >
> > > > generated later in  a separate loop.)
> > > > What actually happens, is that, due to the single quotation marks,
> > > >        
> > the
> >    
> >
> > > > macros containing the names of the temporary variables are subsituted
> > > >        
> > > by
> > >      
> > >
> > > > their content (which should not happen), so the content of the
> > > >        
> > > resulting
> > >      
> > >
> > > > macro is " i.land|ldep0  i.land|ldep1  i.land|ldep2 ", which cannot
> > > >        
> > be
> >    
> >
> > > used
> > >      
> > >
> > > > to refer to temporary variables. For the same reason, it is not
> > > >        
> > > possible to
> > >      
> > >
> > > > define a local macro with a string as content which starts and ends
> > > >        
> > > with
> > >      
> > >
> > > > quotation marks. I found no way to avoid the unintended macro
> > > >        
> > > substitution
> > >      
> > >
> > > > using "\" or compound quotes. Any recommendation is highly
> > > >        
> > > appreciated.
> > >      
> > *
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> >
> >    
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>  

--
Christoph Birkel, M.A.
Wissenschaftlicher Mitarbeiter
-Studienfachberater BA-Studieng�nge Soziologie-
Martin-Luther-Universit�t Halle-Wittenberg
Institut f�r Soziologie
D-06099 Halle (Saale)
GERMANY
Tel.: ++ 49 3 45 / 55 24 22 5
Fax.: ++ 49 3 45 / 55 27 14 9 
http://www.soziologie.uni-halle.de/birkel/



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