I'm trying to understand why this small piece of code does not work as expected. I would expect it to print out "foo", but in fact what I get is
CL-USER> (stringloop)
null output T
line output NIL
NIL
I expect I am using do
wrong, but I've not be able to figure out what.
(defun stringloop ()
(with-input-from-string (s "foo" :index j )
(do ((line (read-line s nil) ;; var init-form
(read-line s nil))) ;; step=form
((null line) (progn (format t "null output ~a~% "(null line)) (format t "line output ~a~% " line))))))
You didn't put anything in the loop body. Your function reads a line ( "foo"
), does nothing with it, then reads another line ( nil
), your termination condition becomes true, and you print the null line.
Run this modified version to see what's happening:
(defun stringloop ()
(with-input-from-string (s "foo")
(do ((line (read-line s nil) ;; var init-form
(read-line s nil))) ;; step=form
((null line) (format t "termination condition - line: ~s~% " line))
(format t "in loop - line: ~s~%" line))))
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