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-rw-r--r--net/ricketyspace/sicp/one/thirtytwo.scm36
1 files changed, 36 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/one/thirtytwo.scm b/net/ricketyspace/sicp/one/thirtytwo.scm
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+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+
+(define-module (net ricketyspace sicp one thirtytwo)
+ #:export (factorial simpson))
+
+(define (accumulate combiner null-value term a next b)
+ (if (> a b)
+ null-value
+ (combiner (term a)
+ (accumulate combiner null-value term (next a) next b))))
+
+(define (product term a next b)
+ (accumulate * 1 term a next b))
+
+(define (factorial n)
+ (let ((term (lambda (x) x))
+ (next (lambda (x) (1+ x))))
+ (product term 1 next n)))
+
+(define (sum term a next b)
+ (accumulate + 0 term a next b))
+
+(define (simpson f a b n)
+ (let* ((h (/ (- b a) (* 1.0 n)))
+ (y (lambda (k) (+ a (* k h))))
+ (ce (lambda (k) ;coefficient
+ (cond ((or (= k 0) (= k n)) 1)
+ ((even? k) 2)
+ (else 4))))
+ (term (lambda (k)
+ (* (ce k) (f (y k)))))
+ (next (lambda (k) (1+ k))))
+ (* (/ h 3.0)
+ (sum term 0 next n))))