simply scheme 第十一章 练习
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11.1 (define (downup4 wd) (se wd (bl wd) (bl (bl wd)) (first wd) (bl (bl wd)) (bl wd) wd)) 11.2 (define (count-ums sent) (if(empty? sent) 0 (if(equal? 'um (first sent)) (+ 1(count-ums(bf sent))) (count-ums(bf sent))))) 11.3 (define (phone-unspell wd) (if(empty? wd) '() (accumulate word(se (unspell-letter(first wd)) (phone-unspell (bf wd)))))) 11.4 Marilu Henner 11.5 (define (initials sent) (if(empty? sent) '() (se (first(first sent)) (initials (bf sent))))) 11.6 (define (countdown num) (if(equal? num 0) 'BLASTOFF (se num (countdown (- num 1))))) 11.7 (define (copies num wd) (if(equal? num 0) '() (se wd (copies (- num 1) wd))))