Pairs. Lists 入 (cons12)=>(1.2) car cdr (cons 1(cons 2 0) (list 1 2) (pair?(cons 1 2))(pair?(list 1 2 3)=>#t (list?(cons 1 2)=>#f (list?(cons 10)=> sept.17,2003 16.410/16. More Scheme Sum a list Assuming list is a flat list of numbers return sum.(define(sum I)...) 1st solution -use recursion (define(sum I) (if (null? D) 0 (+(car D)(sum(cdr D ) sept.17,2003 16.410/16. More SchemeSept. 17, 2003 3 Pairs, Lists • • (cons 1 (cons 2 ())) • (list 1 2) ) • (pair? (cons 1 2)) (pair? (list 1 2 3)) => #t • (list? (cons 1 2) => #f (list? (cons 1 ‘())) => #t 1 2 car 2 () car 1 car Sept. 17, 2003 4 Sum a list • Assuming list is a flat list of numbers, return sum. (define (sum l) …) • 1st (define (sum l) (if (null? l) 0 1 2 cdr cdr cdr solution – use recursion. (+ (car l) (sum (cdr l))))) (cons 1 2) => (1 . 2) • () • ‘( 16.410/16.413 More Scheme 16.410/16.413 More Scheme