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;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
;;; ___________________
;;; < fuck abstraction. >
;;; -------------------
;;; \ __
;;; \ (oo)
;;; \ ( )
;;; \ /--\
;;; __ / \ \
;;; UooU\.'@@@@@@`.\ )
;;; \__/(@@@@@@@@@@) /
;;; (@@@@@@@@)((
;;; `YY~~~~YY' \\
;;; || || >>
(define-module (net ricketyspace sicp one thirtythree)
#:use-module (net ricketyspace sicp one twentyeight)
#:export (filtered-accumulate sum-odd sum-prime-sqrs product-relative-primes))
(define (gcd a b)
(if (= b 0)
a
(gcd b (remainder a b))))
(define (filtered-accumulate combiner null-value term a next b filter)
(cond ((> a b) null-value)
((not (filter a))
(combiner null-value
(filtered-accumulate combiner null-value
term (next a) next b
filter)))
(else
(combiner (term a)
(filtered-accumulate combiner null-value
term (next a) next b
filter)))))
(define (sum-odd n)
(let ((null-value 0)
(term (lambda (x) x))
(next (lambda (x) (1+ x))))
(filtered-accumulate + null-value term 0 next n odd?)))
(define (sum-prime-sqrs a b)
"Return sum of prime squares between A and B.
A and B must be an integer greater than zero."
(let ((null-value 0)
(term (lambda (x) (* x x)))
(next (lambda (x) (1+ x))))
(filtered-accumulate + null-value term a next b prime?)))
(define (product-relative-primes n)
(let ((null-value 1)
(term (lambda (x) x))
(next (lambda (x) (1+ x)))
(filter (lambda (x) (= (gcd x n) 1))))
(filtered-accumulate * null-value term 1 next n filter)))
;;; Guile REPL
;;; scheme@(guile-user)> ,use (net ricketyspace sicp one thirtythree)
;;; scheme@(guile-user)> (sum-odd 1)
;;; $9 = 1
;;; scheme@(guile-user)> (sum-odd 5)
;;; $10 = 9
;;; scheme@(guile-user)> (sum-odd 10)
;;; $13 = 25
;;; scheme@(guile-user)> (sum-prime-sqrs 1 5)
;;; $10 = 39
;;; scheme@(guile-user)> (+ 1 4 9 25)
;;; $11 = 39
;;; scheme@(guile-user)> (sum-prime-sqrs 1 10)
;;; $12 = 88
;;; scheme@(guile-user)> (+ 1 4 9 25 49)
;;; $13 = 88
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