Re: String variables

[Hans-Bernhard B. <br...@ph...>]

On Thu, 8 Jul 2004, Ethan Merritt wrote:

> Or did you mean
> 
>     set label 1 sprintf( "After fitting, A = %3.2f, B = %3.2f", A, B)

That one, mostly.  Generally, the "A = $A" syntax may seem simple, but
it's also of rather limited flexibility.   

This function-like syntax also extends more naturally to other operations
on strings (scanning a string, reading a string from an external file,
...).  I think we can take a hint from Java, here: Strings are native
datatypes, but the only operator they support is '+' for concatenation.
Everything else is done by functions.

> But I don't really see how either of these would work on the
> command line. The existing "userstrings" patch allows
> 
>     STYLE1 = "1:4 with lines lw 2"
>     plot 'datafile' using $STYLE1

In this context, the decision about $ vs. sprintf() would affect only the
first of these lines.  In my scheme, it might become:

   STYLE1 = sprintf("1:%d with lines lw %g", i, width)

We should probably foresee an interface to gprintf(), too, to give access 
to %l/%L from 'help format spec'.

> Admittedly the userstrings patch would probably better be
> described as implementing macro definitions rather string variables,

Exactly.  Just storing a fixed string in a variable is not very helpful.
The real power to be gained would lie in the methods for constructing such
strings from other elements.  Compare it to our user-defined variables.  
They would be of rather limited applicability if you couldn't use
arbitrary expressions to compute their value.

> > $ already being used for at 
> > least two entirely unrelated things in gnuplot
> 
> The primary use is for column numbers.
> The second use I know about is for the command line 
> variables ($1, $2, $3...).  

IIRC there's a feature request that we should $-expand environment
variables.  And TeX strings have to be able to contain literal $
characters.  And your own suggestions just introduced two independent uses
of it: to signal a string variable / macro to be expanded, and to signal a
number to be inserted inside a string.

-- 
Hans-Bernhard Broeker (br...@ph...)
Even if all the snow were burnt, ashes would remain.