Part 5: better xy moves, defuns, calling defuns, color

Continued from Emacs Lisp programming pt. 4.

To edit Lisp code in its own buffer, create a buffer, giving it a name something like mycode.el. To make sure Emacs realizes you are editing Lisp, you can type M-x @lisp-mode@. You should now see (Lisp) on the status line at the bottom of the screen. Now type away your code. When you’re happy with it, type M-x @eval-buffer@ to load your code into Emacs. Then create another test buffer in which to run your code (via C-x 5 b as described at the start of the last examples. When you’re in the test buffer, type M-: to get a Lisp prompt at the bottom of the window with which you can run a defun by typing the defun’s name in parentheses.

A helper routine to draw at a given screen position

(defun drawxy (x y sprite)
  (dotimes (j y)
  (dotimes (i x)
    (insert " "))
  (insert sprite))

sprite is the text to draw.

Using the helper function to draw

(defun liner ()
  (dotimes (x 20)
    (drawxy x x "!")
    (sit-for 0.1)))

More elaborate drawing, based on Peter’s code

(defun oVeR-sine ()
  (dotimes (y 777)
    (drawxy (round (+ 10 (* 10 (sin (/ y 10.0)))))
	    (round (+ 10 (* 10 (sin (/ y 13.0)))))
    (sit-for 0.1)))

Make a background grid

(defun background (width height)
  (dotimes (i height)
    (dotimes (j width)
      (insert "."))

Revised drawxy to draw on the grid

(defun drawxy2 (x y sprite)
  (goto-char (point-min))
  (forward-line y)
  (forward-char x)
  (delete-region (point) (+ (point) (length sprite)))
  (insert sprite))

Draw two lines on grid at same time

(defun liner2 ()
  (background 80 40)
  (dotimes (x 20)
    (drawxy2 x x "&")
    (drawxy2 (- 20 x) x "*")
    (sit-for 0.1)))

Using color:

(insert (propertize "foreground color test" 'face '(:foreground "red")))
(insert (propertize "gray background test" 'face '(:background "gray30")))
(insert (propertize "color with hex code" 'face '(:foreground "#33AAFF")))
(insert (propertize "lots of color" 'face '(:foreground "orange" :background "purple")))

To make color work in ielm, first type M-x font-lock-mode. You should see a message at the bottom of the screen Font-Lock mode disabled (if it says enabled, type M-x font-lock-mode again). Or just work in a test buffer which you’ve created.

Continued in Emacs Lisp programming pt. 6.