intraxia/wp-gistpen

;; Calculation of Hofstadter's male and female sequences as a list of pairs

(define (hofstadter-male-female n)
(letrec ((female (lambda (n)
                     (if (= n 0)
                     1
                     (- n (male (female (- n 1)))))))
         (male (lambda (n)
                 (if (= n 0)
                         0
                         (- n (female (male (- n 1))))))))
    (let loop ((i 0))
        (if (> i n)
        '()
        (cons (cons (female i)
                        (male i))
            (loop (+ i 1)))))))

(hofstadter-male-female 8)

(define (find-first func lst)
(call-with-current-continuation
 (lambda (return-immediately)
     (for-each (lambda (x)
             (if (func x)
                     (return-immediately x)))
                 lst)
     #f)))