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; $7.11 (define-syntax fold-of (syntax-rules (range in is) ((_ "z" f b e) (set! b (f b e))) ((_ "z" f b e (v range fst pst stp) c ...) (let* ((x fst) (p pst) (s stp) (le? (if (positive? s) <= >=))) (do ((v x (+ v s))) ((le? p v) b) (fold-of "z" f b e c ...)))) ((_ "z" f b e (v range fst pst) c ...) (let* ((x fst) (p pst) (s (if (< x p) 1 -1))) (fold-of "z" f b e (v range x p s) c ...))) ((_ "z" f b e (v range pst) c ...) (fold-of "z" f b e (v range 0 pst) c ...)) ((_ "z" f b e (x in xs) c ...) (do ((t xs (cdr t))) ((null? t) b) (let ((x (car t))) (fold-of "z" f b e c ...)))) ((_ "z" f b e (x is y) c ...) (let ((x y)) (fold-of "z" f b e c ...))) ((_ "z" f b e p? c ...) (if p? (fold-of "z" f b e c ...))) ((_ f i e c ...) (let ((b i)) (fold-of "z" f b e c ...))))) (define-syntax list-of (syntax-rules () ((_ arg ...) (reverse (fold-of (lambda (d a) (cons a d)) '() arg ...))))) (define div711 (let loop ((d 711) (ds '())) (cond ((zero? d) ds) ((zero? (modulo 711000000 d)) (loop (- d 1) (cons d ds))) (else (loop (- d 1) ds))))) (define n 0) (display (list-of (list a b c d) (a in div711) (b in div711) (<= a b) (c in div711) (<= b c) (d range 79 712 79) (q is (begin (set! n (+ n 1)) n)) (= (+ a b c d) 711) (= (* a b c d) 711000000))) (newline) (display n)
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