Using comment characters for specific major modes

[martin-kemp]

Am using the following expression to make a line composed of ";" of length lena.



The first two semicolons ";;" are for when I use elisp code.



    (setq-local s (concat ";; " (make-string lena ?\;)))



But I want to change the starting ";;" to be the comment character of the major 
mode I am working with.



For texinfo I want "@c", and for fortran-mode I want "c", and "!!" for f90-mode.