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The dotimes Macro

The dotimes macro is similar to dolist, except that it loops a specific number of times.

The first argument to dotimes is assigned the numbers 0, 1, 2 and so forth each time around the loop, and the value of the third argument is returned. You need to provide the value of the second argument, which is how many times the macro loops.

For example, the following binds the numbers from 0 up to, but not including, the number 3 to the first argument, number, and then constructs a list of the three numbers. (The first number is 0, the second number is 1, and the third number is 2; this makes a total of three numbers in all, starting with zero as the first number.)

     (let (value)      ; otherwise a value is a void variable
       (dotimes (number 3 value)
         (setq value (cons number value))))
     
     ⇒ (2 1 0)

dotimes returns value, so the way to use dotimes is to operate on some expression number number of times and then return the result, either as a list or an atom.

Here is an example of a defun that uses dotimes to add up the number of pebbles in a triangle.

     (defun triangle-using-dotimes (number-of-rows)
       "Using dotimes, add up the number of pebbles in a triangle."
     (let ((total 0))  ; otherwise a total is a void variable
       (dotimes (number number-of-rows total)
         (setq total (+ total (1+ number))))))
     
     (triangle-using-dotimes 4)