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The first function should print the X axis tic marks. We must specify the tic marks themselves and their spacing:
(defvar X-axis-label-spacing (if (boundp 'graph-blank) (* 5 (length graph-blank)) 5) "Number of units from one X axis label to next.") |
(Note that the value of graph-blank
is set by another
defvar
. The boundp
predicate checks whether it has
already been set; boundp
returns nil
if it has not.
If graph-blank
were unbound and we did not use this conditional
construction, in GNU Emacs 21, we would enter the debugger and see an
error message saying
`Debugger entered--Lisp error: (void-variable graph-blank)'.)
Here is the defvar
for X-axis-tic-symbol
:
(defvar X-axis-tic-symbol "|" "String to insert to point to a column in X axis.") |
The goal is to make a line that looks like this:
| | | | |
The first tic is indented so that it is under the first column, which is indented to provide space for the Y axis labels.
A tic element consists of the blank spaces that stretch from one tic to
the next plus a tic symbol. The number of blanks is determined by the
width of the tic symbol and the X-axis-label-spacing
.
The code looks like this:
;;; X-axis-tic-element ... (concat (make-string ;; Make a string of blanks. (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) ;; Concatenate blanks with tic symbol. X-axis-tic-symbol) ... |
Next, we determine how many blanks are needed to indent the first tic
mark to the first column of the graph. This uses the value of
full-Y-label-width
passed it by the print-graph
function.
The code to make X-axis-leading-spaces
looks like this:
;; X-axis-leading-spaces ... (make-string full-Y-label-width ? ) ... |
We also need to determine the length of the horizontal axis, which is the length of the numbers list, and the number of tics in the horizontal axis:
;; X-length ... (length numbers-list) ;; tic-width ... (* symbol-width X-axis-label-spacing) ;; number-of-X-tics (if (zerop (% (X-length tic-width))) (/ (X-length tic-width)) (1+ (/ (X-length tic-width)))) |
All this leads us directly to the function for printing the X axis tic line:
(defun print-X-axis-tic-line (number-of-X-tics X-axis-leading-spaces X-axis-tic-element) "Print tics for X axis." (insert X-axis-leading-spaces) (insert X-axis-tic-symbol) ; Under first column. ;; Insert second tic in the right spot. (insert (concat (make-string (- (* symbol-width X-axis-label-spacing) ;; Insert white space up to second tic symbol. (* 2 (length X-axis-tic-symbol))) ? ) X-axis-tic-symbol)) ;; Insert remaining tics. (while (> number-of-X-tics 1) (insert X-axis-tic-element) (setq number-of-X-tics (1- number-of-X-tics)))) |
The line of numbers is equally straightforward:
First, we create a numbered element with blank spaces before each number:
(defun X-axis-element (number) "Construct a numbered X axis element." (let ((leading-spaces (- (* symbol-width X-axis-label-spacing) (length (number-to-string number))))) (concat (make-string leading-spaces ? ) (number-to-string number)))) |
Next, we create the function to print the numbered line, starting with the number "1" under the first column:
(defun print-X-axis-numbered-line (number-of-X-tics X-axis-leading-spaces) "Print line of X-axis numbers" (let ((number X-axis-label-spacing)) (insert X-axis-leading-spaces) (insert "1") (insert (concat (make-string ;; Insert white space up to next number. (- (* symbol-width X-axis-label-spacing) 2) ? ) (number-to-string number))) ;; Insert remaining numbers. (setq number (+ number X-axis-label-spacing)) (while (> number-of-X-tics 1) (insert (X-axis-element number)) (setq number (+ number X-axis-label-spacing)) (setq number-of-X-tics (1- number-of-X-tics))))) |
Finally, we need to write the print-X-axis
that uses
print-X-axis-tic-line
and
print-X-axis-numbered-line
.
The function must determine the local values of the variables used by both
print-X-axis-tic-line
and print-X-axis-numbered-line
, and
then it must call them. Also, it must print the carriage return that
separates the two lines.
The function consists of a varlist that specifies five local variables, and calls to each of the two line printing functions:
(defun print-X-axis (numbers-list) "Print X axis labels to length of NUMBERS-LIST." (let* ((leading-spaces (make-string full-Y-label-width ? )) ;; symbol-width is provided by graph-body-print (tic-width (* symbol-width X-axis-label-spacing)) (X-length (length numbers-list)) (X-tic (concat (make-string ;; Make a string of blanks. (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) ;; Concatenate blanks with tic symbol. X-axis-tic-symbol)) (tic-number (if (zerop (% X-length tic-width)) (/ X-length tic-width) (1+ (/ X-length tic-width))))) (print-X-axis-tic-line tic-number leading-spaces X-tic) (insert "\n") (print-X-axis-numbered-line tic-number leading-spaces))) |
You can test print-X-axis
:
X-axis-tic-symbol
, X-axis-label-spacing
,
print-X-axis-tic-line
, as well as X-axis-element
,
print-X-axis-numbered-line
, and print-X-axis
.
(progn (let ((full-Y-label-width 5) (symbol-width 1)) (print-X-axis '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16)))) |
eval-expression
).
yank)
.
Emacs will print the horizontal axis like this:
| | | | | 1 5 10 15 20 |
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