gnuplot-beta

if (1) b="plot x*x"; @b

[Petr M. <mi...@ph...>]

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

---
PM

Re: if (1) b="plot x*x"; @b

[Thomas S. <t.s...@fz...>]

it's a timing problem, with 'set term x11' nothing is plotted
for 'a' (because 'a' is empty when '@a' is executed),
a second '@a' typed in at the prompt results in a plot.
the same applies to 'b'.


Petr Mikulik wrote:
> 
> 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
> 
> ---
> PM
> 
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Re: if (1) b="plot x*x"; @b

[Ethan A M. <merritt@u.washington.edu>]

On Friday 06 February 2009, Petr Mikulik wrote:
> 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.  

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);



-- 
Ethan A Merritt

Re: if (1) b="plot x*x"; @b

[Petr M. <mi...@ph...>]

> > 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.

---
PM