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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 labeled 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)))