Add one/eight.scm

Exercise 1.8.

1 files changed, 38 insertions, 0 deletions

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+;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;; International. See
+;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+
+(define-module (one eight)
+  #:export (cube double
+            div-three improve
+            good-enough? cbrt-iter
+            cbrt-sicp))
+
+(use-modules (one six))
+
+(define (cube x)
+  (* (square x) x))
+
+(define (double x)
+  (* 2 x))
+
+(define (div-three x)
+  (/ x 3.0))
+
+(define (improve y x)
+  (div-three (+ (/ x (square y))
+                (double y))))
+
+(define (good-enough? y x)
+  (< (abs (- (cube y) x))
+     0.001))
+
+(define (cbrt-iter y x)
+  (if (good-enough? y x)
+      y
+      (cbrt-iter (improve y x)
+                 x)))
+
+(define (cbrt-sicp x)
+  (cbrt-iter 1.0 x))
+