1. List processing

• Lisp != “Lots of Isolated Silly Parentheses”

• Lisp == “LISt Processing”

• List data structure: surrounded by parentheses, preceded by a single apostrophe, elements separated by space(s). List can be nested in another list. Examples:

Open elisp REPL in Emacs: M-x ielm.

'(rose violet daisy buttercup)
'(rose (violet (daisy buttercup)))

• In Lisp, both data and programs are represented the same way:

(+ 2 2)
4
(+ (- 4 1) 1)
4

• Lisp atoms: ‘indivisible’ parts (or elements inside parentheses). Examples: numbers (1, 2, 3); symbols (forward-line), string (“this is a text”).

• The printed representation of both atoms and lists are called symbolic expressions or, more concisely, s-expressions.

• Evaluation: ' means quote, do nothing except return the list itself. If no quote, list are evaluated by the first symbol, aka. function. In Emacs: C-x C-e == eval-last-sexp, or C-j (kind of elisp notebook)

• C-M-x for evaluating Lisp functions.

• Variable: a symbol that has a value attached to it.

Some built-in variables: fill-column

• message function: send messages to users, in echo area.

(message "helo")
"helo"
(message "The name of this buffer %s" (buffer-name))
"The name of this buffer *scratch*"

• Setting value of a variable

;; using set (noted: both variable and value must be quoted unless you want otherwise)
(set 'flowers '(rose violet daisy buttercup))
;; (rose violet daisy buttercup)

;; using setq, automatically quoted the variables
(setq trees '(pine fir oak maple)
      herbivores '(gazelle antelope zebra))
(gazelle antelope zebra) ; last value is returned

2. Practicing Evaluation

This section for Emacs users.

;; get buffer name
(buffer-name)
"elisp-prog.el"

;; name of file associated with the buffer
(buffer-file-name)
"/home/anchu/elisp-prog.el"

;; get the buffer itself
(current-buffer)
#<buffer elisp-prog.el>

;; the most recently selected buffer
(other-buffer)
#<buffer *Messages*>

;; jump the other buffer
(switch-to-buffer (other-buffer))

;; number of characters in the buffer
(buffer-size)
1109

;; current position of cursor
(point)
1124

(point-max)
1143

(point-min)
1