Format: (defun <name> (<par1> <par2> ... <parN>) <body>)
Required arguments: 2
<name>: a symbol which is appropriate as the name of funtion; (<par1> <par2> ...): a list of zero or more symbols which are appropriate as parameter names
Optional arguments: 1
<body>: a sequence of zero or more LISP expressions
The arguments to defun are not evaluated---they are used to establish a procedure definition. The first argument is a symbol which specifies the name of the function. This name can later be used to execute the <body> of the function. The parameter-list follows the name. This list specifies the number and order of arguments in a function call. Each <par> is symbol which may appear in the <body>. The value of each parameter, <par>, is determined by the value of corresponding argument in the function call. defun returns the name of the function.
Examples:
> (defun square (x)
(* x x))
SQUARE
> (square 4)
16
> (square (+ 7 -2))
25
> (defun equal-length (lst1 lst2)
(cond ((= (length lst1) (length lst2)) t)
(t nil)))
EQUAL-LENGTH
> (equal-length '(a b c) '((d e) f g))
T
> (equal-length '() (rest '(a b)))
NIL
> (defun side-effect (x y)
(setq x (* x x x))
(+ x y))
SIDE-EFFECT
> (side-effect 2 3)
11
> (side-effect -4 14)
50
© Colin Allen & Maneesh Dhagat