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I've got this function
(defun mt ()
(dotimes (x 20)
(dotimes (y 20)
(format "%3d " (* (1+ x) (1+ y))))
(format "\n")))
in my *scratch*. a Ctr-= prints back mt. But then evaluating (mt) only prints back nil. How would I get it to print out the multiplication table? This works in Common Lisp at the REPL. I know I'm missing something basic here...
format generates a string, but it doesn't do anything with it. You probably want to pass the result of format on to something that does:
(defun mt ()
(dotimes (x 20)
(dotimes (y 20)
(insert (format "%3d " (* (1+ x) (1+ y)))))
(insert (format "\n"))))
I think you're also confused about how dotimes works. From the doc string:
(dotimes (VAR COUNT [RESULT]) BODY...)
:around advice: ‘cl--wrap-in-nil-block’
Loop a certain number of times. Evaluate BODY with VAR bound to successive integers running from 0, inclusive, to COUNT, exclusive. Then evaluate RESULT to get the return value (nil if RESULT is omitted).
Without a results argument, dotimes will only produce side-effects (modifying variables or state) if you explicitly tell it to, as I have above by adding the insert forms. If you add a results argument, you can use that variable to return a value.
To get the behaviour you expect, we need to add result and some code to modify it:
(defun mt ()
(let ((res ""))
(dotimes (x 20 res)
(dotimes (y 20)
(setq res
(concat res (format "%3d " (* (1+ x) (1+ y))))))
(setq res
(concat res (format "\n"))))))
This form will return the table you have constructed, which you can then do what you like with.
(format "%5d is padded on the left with spaces" (+ 1 3)) produce output in scratch and my mt function not?
C-j in the scratch buffer does is evaluate the previous expression, convert that value to a string and then insert the string into the scratch buffer. So it's C-j that does the actual adding of text to the scratch buffer; merely evaluating (format ...) (as happens when a function calls format) just makes a string (in your computer's memory somewhere) but doesn't insert the string in any buffer.
C-j in scratch, so I don't get the default behaviour anymore. I've been using eval-last-sexp, not eval-print-last-sexp.
eval-last-sexp and eval-print-last-sexp but someone must have considered keeping the behaviors separate important and useful...
I'd probably use a different approach, using mapconcat to apply the function and concatenate the results:
(let ((range (number-sequence 1 20)))
(mapconcat
(lambda (y)
(mapconcat
(lambda (x)
(format "%03d" (* x y)))
range " "))
range "\n"))
This returns the string that you can insert or whatever else.
mt function other than mine's a function?
dotimes returns the value of the third element of its first argument after finishing the iterations, it doesn't evaluate it for each iteration.
(format "%..." ...)is equivalent to Common Lisp(format nil "%..." ...). See also (elisp) Output Streams and (elisp) Output Functions