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#lang racket
;;; Exercise 01
(define (10^len n)
(if (= n 0)
1
(* (10^len (quotient n 10)) 10)))
(define (substr? a b)
(define (calc-iter b comp)
(cond [(= b 0) #f]
[(= (remainder (- b a) comp) 0) #t]
[else (calc-iter (quotient b 10) comp)]))
(calc-iter b (10^len a)))
(substr? 123 5123783)
;;; Exercise 02
(define (my-identity x)
x)
(define (my-compose f g)
(lambda (x) (f (g x))))
(define (my-negate p?)
(not p?))
(define (my-curry f x)
((curry f) x))
;;; Exercise 03
(define (difference F a b)
(- (F a) (F b)))
;;; Exercise 04
(define f
(lambda (x) (* 2 x)))
;;; Exercise 05
(define (derive f eps)
(lambda (x) (/ (- (f (+ x eps)) (f x)) eps)))
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