using with_stdout using a variable for filename

Hello,

i am trying to write data to a file like this:

define_variable( gnuplot_temp_file, "maxima-temp.dat", string);
with_stdout( gnuplot_temp_file, "hello");

but that does not seem to work, because with_stdout is a macro.
how can i use with_stdout with a variable filename?


Thanks for hints,
Robert