#### C.2.3 Create a Y Axis Column

The preceding functions provide all the tools needed to construct a
function that generates a list of numbered and blank strings to insert
as the label for the vertical axis:

(defun Y-axis-column (height width-of-label)
"Construct list of Y axis labels and blank strings.
For HEIGHT of line above base and WIDTH-OF-LABEL."
(let (Y-axis)
(while (> height 1)
(if (zerop (% height Y-axis-label-spacing))
;; Insert label.
(setq Y-axis
(cons
(Y-axis-element height width-of-label)
Y-axis))
;; Else, insert blanks.
(setq Y-axis
(cons
(make-string width-of-label ? )
Y-axis)))
(setq height (1- height)))
;; Insert base line.
(setq Y-axis
(cons (Y-axis-element 1 width-of-label) Y-axis))
(nreverse Y-axis)))

In this function, we start with the value of `height`

and
repetitively subtract one from its value. After each subtraction, we
test to see whether the value is an integral multiple of the
`Y-axis-label-spacing`

. If it is, we construct a numbered label
using the `Y-axis-element`

function; if not, we construct a
blank label using the `make-string`

function. The base line
consists of the number one followed by a tic mark.