When is the format actually printed in Common Lisp?

Question

I have the following general Lisp code:

(defun micro-read-eval-print () (format t "Micro > ") (let ((form (read-line))))) 

When I run it, I get the following:

 CL-USER> (micro-read-eval-print) (m-quote a) Micro > NIL 

Note that I typed "(m-quote a)" and the Lisp interpreter prints "Micro> NIL".

Now I expected these events to happen in reverse order. I would expect Micro to be printed first, as format approval will be indicated first. Why is it not printed first? And what do I need to do to make sure it is printed first?

Answer 1

Try to add

 (defun micro-read-eval-print () (format t "Micro > ") (finish-output) (let ((form (read-line))))) 

I believe that you are faced with buffering the standard io (stdio), which in C usually bypasses through fflush() in this language.

finish-output seems to be the general Lisp equivalent of the C fflush standard library.