Describes Local and global variables in Lisp

1. Ranjitha M
Department of Computer Science [PG]
Kristu jayanti College[Autonomous]
Bengaluru
Lisp -Local Variables

2. Constructs for local variables
->(setq ‘(a b c))
(A B C)
->(setq ‘(d e f))
(D E F)
->(defun local-var (x)
(setq y(cons x y)))
LOCAL –VAR
->(local-var 6)
(6 A B C)
->x
(D E F)
->y
(A B C)
->
 x variable is local and the variable y is global.
 It is accessible from any procedure and retains its value unless reset with setq.

3.  The let and prog constructs also permits the creation of local variables.
Syntax:
(let ((var1 val1) (var2 val2)…) <s-expressions>)
->(let((x ‘a)
(y ‘b)
(z ‘c))
(cons x (cons y (list z))))
(A B C)
->
->(defun memb (el 1st)
(prog ()
start
(cond ((equal el (car 1st )) (return 1st)))
(setq 1st (cdr 1st))
(go start)))
MEMB
->

4. ITERATION AND RECURSION
 (do(<var1 val1> <var-update1>)
(<var2 val2> <var-update2>)
. .
(<test> <return-value>)
(<s-expressions>))
->(defun factorial(n)
(do ((count n (- count 1))
(product n(* product (- count 1))
((equal 0 count) product)))
FACTORIAL
->
 Loop has a simple form
(loop <s-expression>)

5. Recursion
->(defun factorial (n)
(cond ((zerop n) 1)
(t (* n(factorial(- n 1))))))
FACTORIAL
->(factorial 6)
720
->
->(defun newmember (el 1st )
(cond ((null 1st ) nil)
((equal el (car 1st )) 1st )
((t (newmember el (cdr 1st)))))
NEWMEMBER
->