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Programming in Emacs Lisp

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Changes for the Final Version

The final version is different from what we planned in two ways: first, it contains additional values calculated once in the varlist; second, it carries an option to specify the labels' increment per row. This latter feature turns out to be essential; otherwise, a graph may have more rows than fit on a display or on a sheet of paper.

This new feature requires a change to the Y-axis-column function, to add vertical-step to it. The function looks like this:

 
;;; Final version.
(defun Y-axis-column
  (height width-of-label &optional vertical-step)
  "Construct list of labels for Y axis.
HEIGHT is maximum height of graph.
WIDTH-OF-LABEL is maximum width of label.
VERTICAL-STEP, an option, is a positive integer
that specifies how much a Y axis label increments
for each line.  For example, a step of 5 means
that each line is five units of the graph."
  (let (Y-axis
        (number-per-line (or vertical-step 1)))
    (while (> height 1)
      (if (zerop (% height Y-axis-label-spacing))
          ;; Insert label.
          (setq Y-axis
                (cons
                 (Y-axis-element
                  (* height number-per-line)
                  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
                        (or vertical-step 1)
                        width-of-label)
                       Y-axis))
    (nreverse Y-axis)))

The values for the maximum height of graph and the width of a symbol are computed by print-graph in its let expression; so graph-body-print must be changed to accept them.

 
;;; Final version.
(defun graph-body-print (numbers-list height symbol-width)
  "Print a bar graph of the NUMBERS-LIST.
The numbers-list consists of the Y-axis values.
HEIGHT is maximum height of graph.
SYMBOL-WIDTH is number of each column."
  (let (from-position)
    (while numbers-list
      (setq from-position (point))
      (insert-rectangle
       (column-of-graph height (car numbers-list)))
      (goto-char from-position)
      (forward-char symbol-width)
      ;; Draw graph column by column.
      (sit-for 0)
      (setq numbers-list (cdr numbers-list)))
    ;; Place point for X axis labels.
    (forward-line height)
    (insert "\n")))

Finally, the code for the print-graph function:

 
;;; Final version.
(defun print-graph
  (numbers-list &optional vertical-step)
  "Print labelled bar graph of the NUMBERS-LIST.
The numbers-list consists of the Y-axis values.

Optionally, VERTICAL-STEP, a positive integer,
specifies how much a Y axis label increments for
each line.  For example, a step of 5 means that
each row is five units."
  (let* ((symbol-width (length graph-blank))
         ;; height is both the largest number
         ;; and the number with the most digits.
         (height (apply 'max numbers-list))
         (height-of-top-line
          (if (zerop (% height Y-axis-label-spacing))
              height
            ;; else
            (* (1+ (/ height Y-axis-label-spacing))
               Y-axis-label-spacing)))
         (vertical-step (or vertical-step 1))
         (full-Y-label-width
          (length
           (concat
            (number-to-string
             (* height-of-top-line vertical-step))
            Y-axis-tic))))

    (print-Y-axis
     height-of-top-line full-Y-label-width vertical-step)
    (graph-body-print
     numbers-list height-of-top-line symbol-width)
    (print-X-axis numbers-list)))


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