The programming language LISP: Its operation and applications: E. C. Berkeley and D. G. Bobrow (editors). The M.I.T. Press, 1966. $5.00

Your s t y l e i s deve loped by a s e r i e s o f c h o i c e s . Which do you write, "O" o r "NIL"? They compi le i n t o i d e n t i c a l d a t a s t r u c t u r e s ; s o choos ing one o v e r t h e o t h e r i s a m a t t e r o f s t y l e . Do you p u t commas i n your l i s t s , o r do you s e p a r a t e t h e items w i t h s p a c e s ? The l i s t s w i l l l ook t h e same i n s i d e t h e machine whether you p u t t h e commas i n o r l e a v e them o u t ; s o i t ' s n o t a m a t t e r of e f f i c i e n c y , i t ' s a m a t t e r o f s t y l e . I f you had t o write t h e v a l u e o f cons[(^ B) ; (C D)]", which way would you write i t : And which o f t h e s e e x p r e s s i o n s would you write: A l 1 o f t h e s e c h o i c e s c o n t r i b u t e t o your s t y l e . Cho ice o f t h e Program F e a t u r e o r F u n c t i o n a l s To h e l p i n t h e d e v e l o p i n g o f a good s t y l e , 1 am g o i n g t o d i s c u s s two o f t h e more complex c h o i c e s you can make i n LISP. ( 1 ) Shou ld you use t h e program f e a t u r e ? ( 2 ) Should you u s e f u n c t i o n a l s ? I ' m n o t s a y i n g you s h o u l d a lways use t h e program f e a t u r e , and I ' m n o t s a y i n g you s h o u l d never u s e i t . But i t i s d e s i r a b l e t o make t h e c h o i c e c o n s c i o u s l y i n each case , w i t h o u t f e e l i n g t h a t i t must b e w r i t t e n one way o r t h e o t h e r . 1 happen t o f a v o r u s i n g t h e program f e a t u r e and n o t u s i n g f u n c t i o n a l s , b u t t h e c h o i c e s a r e up t o you. The program f e a t u r e i s n o t g i v e n much a t t e n t i o n i n t h e manua l ; t h e f i r s t ment ion o f i t i s on page 29. But any f u n c t i o n t h a t can b e w r i t t e n w i t h o u t t h e program f e a t u r e i s a f u n c t i o n t h a t can be w r i t t e n w i t h t h e program f e a t u r e . A t r i v i a l way i s t o t a k e a f u n c t i o n d e f i n e d a s "X[[x]; ---1" and r e w r i t e i t a s " ~ [ [ x ] ; p rog[ [ ] ; r e t u r n [ I l ] " . The r e s u l t i n g f u n c t i o n w i l l be equ iva l e n t t o t h e o r i g i n a l . The r e v e r s e i s a l s o t r u e any f u n c t i o n w r i t t e n w i t h t h e program f e a t u r e can be w r i t t e n w i t h o u t . 1 w i l l g i v e below some examples o f f u n c t i o n s w r i t t e n w i t h and w i t h o u t t h e program f e a t u r e , and then some examples o f funct i o n s w r i t t e n w i t h and w i t h o u t f u n c t i o n a l s . The f i n a l examples i l l u s t r a t e changes i n bo th a s p e c t s o f s t y l e a t t h e same t i m e . I n t h e append ix , 1 have i n c l u d e d S e x p r e s s i o n t r a n s l a t i o n s o f t h e f i r s t 5 examples . You may u s e t h e program f e a t u r e o r you may n o t u s e i t ; you may u s e f u n c t i o n a l s o r you may n o t u s e them. The examples below a r e t o h e l p you choose your s t y l e .