Function Example

(defun last (L)
  "The last element in a list"
  (if (not L)
      nil
    (if (not (cdr L))
        (car L)
      (last (cdr L)))))
(last ())         ;->  nil
(last '(1))       ;->  1
(last '(1 2 3 4)) ;->  4

Input Statements

• read - reads a value from a stream specified as argument and returns the value.
• The value entered can be an elisp expression using any existing symbols or a constant.
• By default the stream is the standard-input which is the minibuffer. It can be made to point to a file or another buffer.
• (setq n (read))
  reads something from the minibuffer and stores it in n. An optional parameter can specify the format.

Output Statements

• prin1 - prints the evaluation of the expression and returns its value.
• print - similar to prin1 but introduces a new line before and after the printed line.
• princ - similar to prin1 but a string is not printed in quotes.
• All of them can have a stream parameter. By default this is the standard-output and translates into the current file where the expression is evaluated. The parameter can be another buffer or a file.
• An optional parameter can specify the format.
  (prin1 "hello world") ; "hello world""hello world"
  (princ "hello world") ; hello world"hello world"

Loop: dotimes

(dotimes (counter limit result)
   sequence of expressions)

• Repeats the sequence of expressions for a number of times given by the limit.
• Counter is a local variable that is initialized to 0 and incremented at each iteration.
• The expression result is returned at the end of the loop (optional).

Example

(defun factorial (n)
  (let ((f 1))
    (dotimes (i n f)
      (setq f (* f (+ i 1))))))

(factorial 5) ;-> 120
(factorial 1) ;-> 1
(factorial 0) ;-> 1

Loop: dolist

(dolist (variable list result)
  sequence of expressions)

• Executes the sequence of expressions for each member of the list.
• During each iteration, the value of the list element can be found in the variable.
• At the end of the loop, the value of the result is returned (optional).

Example

(defun maxl (L)
  "Returns the maximum element of a list."
  (let ((m nil))
    (dolist (x L m)
      (if (or (not m) (> x m))
          (setq m x)))))

(maxl ())            ;-> nil
(maxl '(3 2 6 54 1)) ;-> 54
(maxl '(1))          ;-> 1