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List:       gnuplot-info-beta
Subject:    Re: if (1) b="plot x*x"; @b
From:       Petr Mikulik <mikulik () physics ! muni ! cz>
Date:       2009-02-06 17:48:47
Message-ID: Pine.LNX.4.64.0902061842440.16750 () monoceros ! physics ! muni ! cz
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> > There is a strange error happening with a not-yet-used variable:
> > 
> > gnuplot> load 'bug.gp'
> >          "bug.gp", line 4: warning: b is not a string variable
> > 
> > where bug.gp:
> > 
> > set macros
> > a=''
> > if (1) a="plot x"; @a
> > if (1) b="plot x*x"; @b
> 
> This has always been a limitation on the use of macros.
> The substitution is done for each whole line as the line
> is read in, before any of the commands on that line have
> been executed.  

I see; a better demonstration of this effect it rather this one:

set macros
a='print 789'
if (1) a="print 123"; @a
if (1) b="print 456"; @b

The solution seems to be:

set macros
if (1) b="print 999"
if (1) @b


> For most purposes, the use of macros has been entirely supplanted
> by string variables. In the case above:
> 
>  if (1) a="plot x";  evaluate(a)

Thanks for this hint, it works fine in gnuplot-cvs.
Finally I had to use the construct with macros because the script had to run 
on gnuplot 4.2.x.

---
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