Add an Elisp "cheatsheet"

1 files changed, 28 insertions, 0 deletions

diff --git a/guides/emacs/elisp-demos.org b/guides/emacs/elisp-demos.org
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+Some terse "context-free" Emacs Lisp snippets that hopefully speak for
+themselves.
+
+* The prefix argument
+#+begin_src elisp
+(defun my/prefix-arg-demo (arg)
+  (interactive (list current-prefix-arg))
+  (insert
+   (let ((num (prefix-numeric-value arg)))
+    (format "%s	%d	%s\n"
+           arg
+           num
+           (cond ((null arg)     "N/A")
+                 ((numberp arg)  (format "M-%d or C-u %d" arg arg))
+                 ((equal arg '-) (format "M-- or C-u -"))
+                 ((listp arg)
+                  (if (< num 0)
+                      (format "(M-- or C-u -) C-u × %d" (log (- num) 4))
+                    (format "C-u × %d" (log num 4)))))))))
+#+end_src
+#+begin_example
+nil	1	N/A
+2	2	M-2 or C-u 2
+-	-1	M-- or C-u -
+(-16)	-16	(M-- or C-u -) C-u × 2
+(64)	64	C-u × 3
+#+end_example
+