rotate-yank-pointer function changes the element in the kill
ring to which
kill-ring-yank-pointer points. For example, it can
kill-ring-yank-pointer from pointing to the second
element to point to the third element.
Here is the code for
(defun rotate-yank-pointer (arg) "Rotate the yanking point in the kill ring." (interactive "p") (let ((length (length kill-ring))) (if (zerop length) ;; then-part (error "Kill ring is empty") ;; else-part (setq kill-ring-yank-pointer (nthcdr (% (+ arg (- length (length kill-ring-yank-pointer))) length) kill-ring)))))
The function looks complex, but as usual, it can be understood by taking it apart piece by piece. First look at it in skeletal form:
(defun rotate-yank-pointer (arg) "Rotate the yanking point in the kill ring." (interactive "p") (let varlist body...)
This function takes one argument, called
arg. It has a brief
documentation string; and it is interactive with a small `p', which
means that the argument must be a processed prefix passed to the
function as a number.
The body of the function definition is a
let expression, which
itself has a body as well as a varlist.
let expression declares a variable that will be only usable
within the bounds of this function. This variable is called
length and is bound to a value that is equal to the number of
items in the kill ring. This is done by using the function called
length. (Note that this function has the same name as the
length; but one use of the word is to name the
function and the other is to name the variable. The two are quite
distinct. Similarly, an English speaker will distinguish between the
meanings of the word `ship' when he says: "I must ship this package
immediately." and "I must get aboard the ship immediately.")
length tells the number of items there are in a list,
(length kill-ring) returns the number of items there are in the
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