Print output into a file or not print output?

Question

I\'d like to save or ignore outputs when I execute a specific function in lisp. I use Emacs and CCL. For example,

(defun foo (x) (format t \"x = ~s~%\" x))
         


        

Answer 1

I'm not sure I understand your question, but the second argument to format is a stream. If you set it to t it prints to standard output, but you can also set it to an open file.

So something like this would allow you to select where the output goes:

;;output to file:
(setf *stream* (open "myfile" :direction :output
                              :if-exists :supersede)

;;alternative to output to standard output:
;;(setf *stream* t)

(defun foo (x) (format *stream* "x = ~s~%" x))

(foo 10)
(close *stream*) ;; only if output sent to a file